These are the some of the steps that you CAN take to reduce your personal global warming footprint. They may appear small, but when you share them with your friends and workmates you will, together, make a huge difference. The figures on the left are the approximate kilograms of greenhouse gasses saved per year for each action. Not only will these save tons of pollutants, but you will save also $3,000 a year, minimum!
Below this list we discuss how to get green energy, organisations to join and other actions.
5300
Shift to Green-Power. For answers to questions see below.
3800
Change from your SUV to a hybrid car. Visit the Green Vehicle Guide
2500
Install solar power, and sell your surplus back to the grid. To support rebates.
2000
Replace electric hot water heating with solar, even with electric booster.
1500
Switching off your computer when not in use, especially big ones.
1080
Recycling just half of your household waste
1000
Plant a native tree, long-term potential as it grows. Here is one way to do this.
900
Adjust you winter thermostat down by 2 degrees, and wear a singlet
860
Insulate your roof space and under the floor, minimum 100mm batts`
720
Carpooling for only 2 days a week
700
Walk your kids to school - healthy for both of you.
700
If you have more than one car, drive the one with the smaller engine.
700
Walk, bike and bus or train instead of car. Information at TravelSmart website
700
Use a fan or evaporative coolers in summer, not air conditioning
640
Use a clothesline instead of a dryer, savings less if it is a new dryer.
600
Double-glaze windows.
600
Weather-strip windows and doors to prevent air leaks
600
All machines to be high efficiency, check out the Energy Rating website
500
Wrap an insulation blanket around your water heater, adjust its temperature
500
Turn off the second drinks frig
400
Put fish tank pump on a timer. Experiment and test water result at pool shop
500
Using less hot water by taking 5 minute showers rather than ten minutes.
455
Reduce rubbish 25% (less packaging, reusables, not disposables, recycling)
450
Don’t use your dishwasher at all, wash up by hand.
450
Turn off appliances at the wall so they are not on ‘stand-by’. Check here.
350
Keep the air filter in your car clean – check monthly
300
Turn off 5 lights in hallways and rooms when you’re not in them.
400
Placing air conditioning unit out of the sun and in the shade
450
For ten CFL fluorescent globes instead of incandescent, see more here..
300
Wash clothes in warm or cold water, not hot
160
Regularly clean the air filter in your air conditioner
100
Run your dishwasher or washing machine only with a full load
10
Each appliance left on stand-by, especially TV
10+
Turn off or fix dripping taps - water costs money
8
Recycle a dozen aluminium cans. Alcoa etc use 20% of total Australian power
8
Turn off your mobile phone charger when it isn’t charging
8
Use a reusable bag every time you go shopping
6
Let hot food cool down before putting it into the fridge
3
Turn off the tap while brushing your teeth
These lifestyle decisions would save about 32 tonnes a year for each person.
If every Australian did these things we would (as a country) be
saving 640 million tons each year.
Get Green Energy:
Every one of us CAN actually do something to help stop global warming.
And it’s SO EASY. Here is a real-life account of how one person helped
Flick the Switch to Green – A Personal Account
Over 100,000 Australian households and businesses have already MADE A DIFFERENCE and chosen to switch to Green Energy sources, ie those sources which do not add to greenhouse gas emissions, such as wind, hydro, solar and biomass generated power. YOU CAN too. Here’s how to DO IT…
Check out the types of green energy available in your area.
Pick up the phone and call your Green Energy provider of choice. You can either switch immediately or arrange to receive a quote.
An example of HOW TO SWITCH TO GREEN ENERGY is given for Energy Australia.
Examples of HOW TO OBTAIN A QUOTE FOR GREEN ENERGY: click for Origin Energy and TruEnergy.
Some people have misconceptions: Click below for answers
Does Green power really come from a true green energy source?
Do we have to install solar cells on our roof to apply? - and other misconceptions.
Reduce Transport Emissions:
By choosing a greener vehicle, you can make a real difference.
The Federal government’s Green Vehicle Guide helps you by rating new vehicles based on greenhouse and air pollution emissions.
Can’t get a new car right away? Neutralise Your Carbon Emissions
Sign up with Greenfleet to have the equivalent number of trees planted for the CO2 you emit. Sign your business up, or get your employer to do so.
Change over to LPG that provides about 8% more energy than petrol (as well as lower cost). However, you will attain better fuel consumption only if the engine is optimized for LPG fuel. Reason: LPG has a lower density, intakes less air and thus there is a decrease of power. If all Australians swapped to a hybrid car it would save 76 million tons of CO2 pa.
If everyone keeps idling their cars for 10 minutes a day, it will cost 44,000 kg of carbon.
At the office:
See that lights are turned off when you go home, and ask cleaners to do the same, or install automatic switching to avoid lighting empty spaces for much of the night.
Turn off computers, photocopiers and printers at the wall at the end of the day.
Organisations to Join:
Here follows a list of groups that work across Australia:
Australian Conservation Foundation works towards a society which protects, sustains and restores the environment, and provides healthy air, land, water, and biological diversity; sustainable cities and industries; a nuclear-free Australia; and action to protect the global environment.
The Australian Rainforest Conservation Foundation was founded in 1982, as a national, non-government organisation with headquarters in Brisbane. Its goal, through research, lobbying, public education and grass-roots support, is to protect, repair and restore the rainforests of Australia and to maximise the protection of forest biodiversity.
Bush Heritage is a national, independent, non-profit organisation committed to preserving Australia's biodiversity by protecting the bush. It is Australia's most widely supported national organisation dedicated to protecting species and habitats through the creation of reserves on private land.
Climate Action Network Australia has the aim of globally tackling the planet’s most challenging environmental problems.
Critical Mass organises on the last Friday of every month, in hundreds of cities worldwide, cyclists, bladers and boarders for a rolling celebration of non-motorised transport
Conservation Volunteers Australia involves the community in conservation projects in urban, regional and remote Australia ranging from tree planting; seed collection; endangered species protection; weed control; flora and fauna surveys; walking trail construction; fencing and environmental monitoring.
Earthwatch Australia helps you to go to amazing places while helping scientists understand the effect our behaviour is having on the planet.
Ecosphere aims to provide an affordable, high quality design resource for small business and non-profit organisations. 10% of proceeds go to an environmental organisation of the customer's choice. Ecosphere also offer a substantial discount on website design for environmental organisations.
The Environment Portal provides access to online services and information provided by Australian, State and Local Governments. Information is organised by seven broad environmental themes - Atmosphere, Biodiversity, Coasts and Oceans, Environment Protection, Heritage, Inland Waters, and Land categories.
Environment Online is the initiative of some 20 major environmental advocacy organisations. They are known as the Mittagong Forum enabling communication and information for people with a passion for environmental conservation and sustainability.
Environment Defenders Office in each State and Territory are dedicated to protecting the environment in the public interest. They provide legal representation and advice, take an active role in environmental law reform and policy formulation, and offer a significant education program designed to facilitate public participation.
Environs Australia is the Local Government Environment Network that aims to advance, support and strengthen the participation of Australian Local Governments in the worldwide movement of councils towards local sustainability.
Friends of the Earth is a community-based activist organisation which works towards an ecologically sustainable and socially equitable society.
Global Energy Network works to bring a global strategy for energy production and to aid world peace and sustainable development.
Greenpeace campaigns for national environmental issues.
Native Forest Network is a global, autonomous collective of forest activists, indigenous peoples, conservation biologists, and non-governmental organizations. It functions on a consensus basis and is non-violent, non-hierarchical, and non-patriarchal.
The National River Health Program was established in 1993 to improve the management of Australia's rivers and floodplains for their long-term health and ecological sustainability.
The Wilderness Society is a national, community-based, environmental organisation whose mission is to protect, promote and secure the future of wilderness and other high conservation areas.
Woodchip Boycott is a campaign that relies on the consumer and investment power of ordinary people to take change to the "marketplace".
World Wide Fund for Nature Australia is working with communities, governments, individuals and businesses to conserve the biological diversity of Australia and the Oceania region.
Monday, September 15, 2008
Gulf Stream Collapse
Extinction is OUR choice, unless...
.... within the next 8 years we have STOPPED using fossil fuels, PLANTED millions of trees, ended logging,
and PREPARED our cities and agriculture for the inevitable sea rise.
OTHERWISE OUR CHILDREN MAY NOT SURVIVE
The Gulf Stream has slowed by 6 million tonnes of water per second over the past 30 years. Many scientists are worried that this portends a collapse and have applied computer models to work out the alternatives. These show there is a 50% chance the current will collapse totally when global temperatures rise by 3°C.
The waters that flow from the Antarctic to the north on the surface of the Atlantic are warm and lose water by evaporating, and therefore get saltier. Salt water is heavier than fresh water and when it reaches the north Atlantic it would sink were it not that the cold water from the arctic is denser still. The arctic water sinks under the warm and provides the force that drives the conveyor and creates the Gulf Stream.
One scenario presented recently to the Pentagon posits that a Gulf Stream collapse could begin in a few years. That massive current of warm water would no longer reach far into the North Atlantic. This would seriously disrupt the temperate climate of Europe and the east coast of North America. The probable outcome would be that the climate of the UK that is now 8°C warmer than the same latitudes in other parts of the world would become closer to that in Russia.
The lesser impact would be a 500mm ocean rise as water heats up.
It is not clear what type of weather would follow a collapse. Some forecasters believe the globe would continue to heat, others predict a new ice age or a global drought. The best models suggest there would be a 5°F drop over Asia and North America and up to 6°F in Europe. On the other hand there would be an increase by up to 4°F in Australia, South America, and south Africa.
Winter storms and cyclonic winds would intensify, amplifying the impact of the changes. Average annual rainfall in Europe and China could decrease by nearly 30%. Europe’s climate would then become more like Siberia’s bringing harsh conditions for agriculture.
No chance then for a reduction in heating loads, and so
CO2 emissions would increase further.
YOU can prevent further warming NOW
Personally and Politically (Click below)
PERSONALLY
POLITICALLY
.... within the next 8 years we have STOPPED using fossil fuels, PLANTED millions of trees, ended logging,
and PREPARED our cities and agriculture for the inevitable sea rise.
OTHERWISE OUR CHILDREN MAY NOT SURVIVE
The Gulf Stream has slowed by 6 million tonnes of water per second over the past 30 years. Many scientists are worried that this portends a collapse and have applied computer models to work out the alternatives. These show there is a 50% chance the current will collapse totally when global temperatures rise by 3°C.
The waters that flow from the Antarctic to the north on the surface of the Atlantic are warm and lose water by evaporating, and therefore get saltier. Salt water is heavier than fresh water and when it reaches the north Atlantic it would sink were it not that the cold water from the arctic is denser still. The arctic water sinks under the warm and provides the force that drives the conveyor and creates the Gulf Stream.
One scenario presented recently to the Pentagon posits that a Gulf Stream collapse could begin in a few years. That massive current of warm water would no longer reach far into the North Atlantic. This would seriously disrupt the temperate climate of Europe and the east coast of North America. The probable outcome would be that the climate of the UK that is now 8°C warmer than the same latitudes in other parts of the world would become closer to that in Russia.
The lesser impact would be a 500mm ocean rise as water heats up.
It is not clear what type of weather would follow a collapse. Some forecasters believe the globe would continue to heat, others predict a new ice age or a global drought. The best models suggest there would be a 5°F drop over Asia and North America and up to 6°F in Europe. On the other hand there would be an increase by up to 4°F in Australia, South America, and south Africa.
Winter storms and cyclonic winds would intensify, amplifying the impact of the changes. Average annual rainfall in Europe and China could decrease by nearly 30%. Europe’s climate would then become more like Siberia’s bringing harsh conditions for agriculture.
No chance then for a reduction in heating loads, and so
CO2 emissions would increase further.
YOU can prevent further warming NOW
Personally and Politically (Click below)
PERSONALLY
POLITICALLY
The Atlantic heat conveyor
The ocean helps shape climate around the world. Ocean currents transport heat from equator towards the poles, releasing heat to the atmosphere and influencing regional rainfall patterns.
The ocean circulation - a global system of surface and deep currents - is powered by two different 'engines'. Movement in the top few hundred to a thousand metres is driven mainly by the prevailing winds. Vertical circulation is driven by cold, salty water sinking at high latitudes, returning towards the equator at depth and being replaced by warm water moving towards the poles at the surface. This is known as the thermohaline circulation (or THC) from the combination of temperature (~thermo) and saltiness (~haline) that controls high-latitude sinking. The flow we can measure is a combination both systems - the wind-driven circulation and the THC.
It is not possible to measure the THC directly. Instead we can get an idea of its strength by measuring what is known as the meridional overturning circulation (MOC) - the flow at different depths, for the full width of the Atlantic. One of the most important aims of RAPID is to monitor this flow.
Why the Atlantic is special
The Atlantic is the only ocean where heat is transported north across the equator. Here warm surface water from the tropics reaches further north than in anywhere else. The relatively warm, salty water of the Gulf Stream system remains at the ocean surface west of Svalbard to a latitude of about 80 degrees before it dips underneath the much fresher and less dense polar water. The heat released by this warm water makes the climate in regions bordering the eastern North Atlantic warmer than at similar latitudes elsewhere. The results of this warm flow can also be seen in the extent of Arctic Sea ice, which differs markedly from that in the Pacific region of the Arctic. The effect of this Atlantic heat conveyor is most noticeable in winter.
The relative warmth of the northern North Atlantic is due to the unique role this ocean plays in the thermohaline circulation. Cold, dense water sinking in the northern North Atlantic drives the Northern Hemisphere loop of the THC. In the Pacific there is no such area where salty subtropical water can travel far enough north and cool down sufficiently to sink. A slow-down in of the North Atlantic loop of the thermohaline circulation may therefore have consequences not just for the North Atlantic region, but for the entire global heat conveyor.
How could the THC slow down?
The North Atlantic loop of the THC is controlled by the sinking of dense (cold and salty) water at high latitudes. The density of seawater is a result of both temperature and salinity (salty water is denser than fresh water, and cold water denser than warm water). Although the Gulf Stream water is saltier than the deep water below, it is much warmer, so its density is lower, and it remains on the surface. On its journey north, the water releases heat to the atmosphere, and cools gradually, until it is cold enough for its density to match that of the deep layer. Sinking can begin.
At this stage the surface water is still warmer than the deep water, but it also saltier, so its density matches that of the deeper water, allowing the two layers to mix. Should the surface water freshen for some reasons, it would have to cool further before it can sink. Sufficient freshwater input might reduce salinity to the extent that the surface water could not possibly sink, even at sub-zero temperatures.
Paradoxically global warming could create precisely this effect. Increased rainfall, melting of sea ice, glaciers and the Greenland ice sheet are all possible consequences of higher temperatures, and could reduce North Atlantic surface salinity sufficiently to slow down or even stop the formation of deep water. If this happens, the THC may shut down. Once stopped, the heat conveyor may take time to recover, and the consequences would be a cooling of northwest Europe.
The ocean circulation - a global system of surface and deep currents - is powered by two different 'engines'. Movement in the top few hundred to a thousand metres is driven mainly by the prevailing winds. Vertical circulation is driven by cold, salty water sinking at high latitudes, returning towards the equator at depth and being replaced by warm water moving towards the poles at the surface. This is known as the thermohaline circulation (or THC) from the combination of temperature (~thermo) and saltiness (~haline) that controls high-latitude sinking. The flow we can measure is a combination both systems - the wind-driven circulation and the THC.
It is not possible to measure the THC directly. Instead we can get an idea of its strength by measuring what is known as the meridional overturning circulation (MOC) - the flow at different depths, for the full width of the Atlantic. One of the most important aims of RAPID is to monitor this flow.
Why the Atlantic is special
The Atlantic is the only ocean where heat is transported north across the equator. Here warm surface water from the tropics reaches further north than in anywhere else. The relatively warm, salty water of the Gulf Stream system remains at the ocean surface west of Svalbard to a latitude of about 80 degrees before it dips underneath the much fresher and less dense polar water. The heat released by this warm water makes the climate in regions bordering the eastern North Atlantic warmer than at similar latitudes elsewhere. The results of this warm flow can also be seen in the extent of Arctic Sea ice, which differs markedly from that in the Pacific region of the Arctic. The effect of this Atlantic heat conveyor is most noticeable in winter.
The relative warmth of the northern North Atlantic is due to the unique role this ocean plays in the thermohaline circulation. Cold, dense water sinking in the northern North Atlantic drives the Northern Hemisphere loop of the THC. In the Pacific there is no such area where salty subtropical water can travel far enough north and cool down sufficiently to sink. A slow-down in of the North Atlantic loop of the thermohaline circulation may therefore have consequences not just for the North Atlantic region, but for the entire global heat conveyor.
How could the THC slow down?
The North Atlantic loop of the THC is controlled by the sinking of dense (cold and salty) water at high latitudes. The density of seawater is a result of both temperature and salinity (salty water is denser than fresh water, and cold water denser than warm water). Although the Gulf Stream water is saltier than the deep water below, it is much warmer, so its density is lower, and it remains on the surface. On its journey north, the water releases heat to the atmosphere, and cools gradually, until it is cold enough for its density to match that of the deep layer. Sinking can begin.
At this stage the surface water is still warmer than the deep water, but it also saltier, so its density matches that of the deeper water, allowing the two layers to mix. Should the surface water freshen for some reasons, it would have to cool further before it can sink. Sufficient freshwater input might reduce salinity to the extent that the surface water could not possibly sink, even at sub-zero temperatures.
Paradoxically global warming could create precisely this effect. Increased rainfall, melting of sea ice, glaciers and the Greenland ice sheet are all possible consequences of higher temperatures, and could reduce North Atlantic surface salinity sufficiently to slow down or even stop the formation of deep water. If this happens, the THC may shut down. Once stopped, the heat conveyor may take time to recover, and the consequences would be a cooling of northwest Europe.
Abrupt Climate Change
Peter Schwartz, Doug Randall
February 2004
"The purpose of this report is to imagine the unthinkable—to push the boundaries of current research on climate change so we may better understand the potential implications on United States national security.
We have interviewed leading climate change scientists, conducted additional research, and reviewed several iterations of the scenario with these experts. The scientists support this project, but caution that the scenario depicted is extreme in two fundamental ways. First, they suggest the occurrences we outline would most likely happen in a few regions, rather than globally. Second, they say the magnitude of the event may be considerably smaller.
We have created a climate change scenario that although not the most likely, is plausible, and would challenge United States national security in ways that should be considered immediately."
This public report, prepared by GBN for the Department of Defense, has been the subject of several news stories. Fortune magazine excerpted the report in its Feb. 9, 2004, issue ("The Pentagon's Weather Nightmare," by David Stipp). The actual report, titled "An Abrupt Climate Change Scenario and Its Implications for United States National Security," was written by Peter Schwartz (GBN chairman) and Doug Randall (co-head of GBN's consulting practice) and is ahttp://www2.blogger.com/img/gl.link.gifttached here in its PDF version. Contrary to some recent media coverage, the report was not secret, suppressed, or predictive.
DOWNLOAD PDF FILE:
Abrupt Climate Change (22 page Public Report)
February 2004
"The purpose of this report is to imagine the unthinkable—to push the boundaries of current research on climate change so we may better understand the potential implications on United States national security.
We have interviewed leading climate change scientists, conducted additional research, and reviewed several iterations of the scenario with these experts. The scientists support this project, but caution that the scenario depicted is extreme in two fundamental ways. First, they suggest the occurrences we outline would most likely happen in a few regions, rather than globally. Second, they say the magnitude of the event may be considerably smaller.
We have created a climate change scenario that although not the most likely, is plausible, and would challenge United States national security in ways that should be considered immediately."
This public report, prepared by GBN for the Department of Defense, has been the subject of several news stories. Fortune magazine excerpted the report in its Feb. 9, 2004, issue ("The Pentagon's Weather Nightmare," by David Stipp). The actual report, titled "An Abrupt Climate Change Scenario and Its Implications for United States National Security," was written by Peter Schwartz (GBN chairman) and Doug Randall (co-head of GBN's consulting practice) and is ahttp://www2.blogger.com/img/gl.link.gifttached here in its PDF version. Contrary to some recent media coverage, the report was not secret, suppressed, or predictive.
DOWNLOAD PDF FILE:
Abrupt Climate Change (22 page Public Report)
Ocean Circulation Shut Down by Melting Glaciers After Last Ice Age
Goddard Space Flight Center
November 19, 2001 - (date of web publication)
At the end of the last Ice Age 13 to 11.5 thousand years ago, the North Atlantic Deep Water circulation system that drives the Gulf Stream may have shut down because of melting glaciers that added freshwater into the North Atlantic Ocean over several hundred years, NASA and university researchers confirm. Since the Gulf Stream brings warm tropical waters north, Western Europe cooled.
The National Science Foundation (NSF) funded study also finds that if a shutdown persisted for a long enough time, the entire Northern Hemisphere would eventually cool.
The computer model simulations of ocean and atmosphere processes used in this study imply a similar phenomenon has the potential to occur in the future due to freshwater additions from increased rain and snow caused by global climate change.
"For the first time, it is shown that realistic additions of glacial meltwater into the North Atlantic would have shutdown North Atlantic Deep Water production over a period of a few hundred years if the initial ocean circulation was somewhat weaker than that of today," said David Rind, lead author of the study and a senior climate researcher at NASA's Goddard Institute for Space Studies in New York, NY. The study appears in the November 16 issue of Journal of Geophysical Research - Atmospheres.
When Rind and his colleagues entered realistic estimates of freshwater from melting glaciers into their model, they found the North Atlantic circulation stopped completely after some 300 years. When the model was adjusted to make the circulation weaker than it is today, cessation of the Gulf Stream took only 150-200 years, matching current estimates based on paleo-climate records .
Freshwater additions into the ocean through the St. Lawrence River have a profound effect on the ocean circulation.
"The more freshwater you add, and the longer you add it, the greater reduction in the North Atlantic circulation," Rind said. "According to our model, this is a linear response."
When the Gulf Stream moves warm surface water from the equator north through the Atlantic, the water cools, gets saltier due to evaporation and becomes very dense. By the time it approaches the coast of Newfoundland, or further northeast in the Norwegian Sea, it becomes dense enough to sink. This process is called overturning. The dense water then slowly travels through the deep water southward into the Southern Hemisphere, with the return flow to the north occurring at the surface.
But when freshwater gets mixed with the salty water in the North Atlantic, it makes the water less dense and slows the overturning process and the ocean circulation.
While the study finds that freshwater input could slow and stop overturning, this would not stop the Gulf Stream entirely. That's because the stream is partially pushed by winds. As a result, the model shows the reduced Gulf Stream would only transport about half as much heat northward, thereby cooling Western Europe. Were this to occur in a global warming scenario, it would act to partly counter the effects of projected greenhouse warming in parts of Western Europe.
Many scientists suspect more rainfall in parts of the Northern Hemisphere during this century as a result of greenhouse warming. That's because warmer temperatures increase the atmosphere's capacity to carry water. "The North Atlantic circulation may already be weakening due to freshwater rainfall additions associated with global warming," Rind said.
But the model shows a number of inconsistencies with previous studies on the last ice age. Those studies speculate that once freshwater stopped flowing, the ocean circulation would return within only a few decades, matching a rapid warming seen in the climate record. The model finds that deepwater circulation does not return for at least hundreds of years when the freshwater additions end. Also contrary to observations, the model showed cooling throughout the Northern Hemisphere; during the last ice age, the majority of the United States land mass did not appear to cool.
"It's hard to understand how parts of the Northern Hemisphere might have cooled to the magnitude suggested, but not North America," Rind said. "That seems to imply that either the paleo-records are being misinterpreted, or something else went on, something major that is not being accounted for. This isn't necessarily the end of the story."
North Atlantic Ocean Circulation System
The North Atlantic Ocean circulation system is very sensitive to freshwater inputs. That's because the Gulf Stream moves warm surface water from the equator north through the Atlantic, where the water cools, gets saltier due to evaporation and becomes very dense. By the time it approaches the coast of Newfoundland, or further northeast in the Norwegian Sea, it becomes dense enough to sink. This process is called overturning. The dense water then slowly travels through the deep water southward into the Southern hemisphere, with the return flow to the North occurring at the surface. Today, the climate of Western Europe is much warmer than equivalent latitudes of North America, because the Gulf Stream provides a lot of warmth to those parts of Europe.
But when freshwater gets mixed into the salty water in the North Atlantic, it makes the water less dense and slows the overturning process and the ocean's circulation. The study finds that freshwater from melting glaciers on land that drained into the North Atlantic Ocean through the St. Lawrence River at the end of the last Ice Age, would have shut down the North Atlantic Deep Water circulation system in several hundred years. This is the circulation that drives the Gulf Stream. Also, the research indicates North Atlantic Deep Water circulation appears to respond linearly to freshwater additions-which means the more freshwater you add, and the longer you add it, the greater reduction in the North Atlantic circulation.
While the study finds that freshwater input could slow and stop overturning, this would not stop the Gulf Stream entirely. That's because the stream is partially pushed by winds. As a result, the computer model used by NASA's David Rind in his study shows the reduced Gulf Stream would only transport about half as much heat northward, thereby cooling Western Europe. Were this to occur in a global warming scenario, where rainfall increases in the Northern Hemisphere due to higher temperatures over the next century, it would act to partly counter the effects of projected greenhouse warming in parts of Western Europe. Credit: Deborah McLean, NASA Goddard Space Flight Center Multimedia Design Studio
November 19, 2001 - (date of web publication)
At the end of the last Ice Age 13 to 11.5 thousand years ago, the North Atlantic Deep Water circulation system that drives the Gulf Stream may have shut down because of melting glaciers that added freshwater into the North Atlantic Ocean over several hundred years, NASA and university researchers confirm. Since the Gulf Stream brings warm tropical waters north, Western Europe cooled.
The National Science Foundation (NSF) funded study also finds that if a shutdown persisted for a long enough time, the entire Northern Hemisphere would eventually cool.
The computer model simulations of ocean and atmosphere processes used in this study imply a similar phenomenon has the potential to occur in the future due to freshwater additions from increased rain and snow caused by global climate change.
"For the first time, it is shown that realistic additions of glacial meltwater into the North Atlantic would have shutdown North Atlantic Deep Water production over a period of a few hundred years if the initial ocean circulation was somewhat weaker than that of today," said David Rind, lead author of the study and a senior climate researcher at NASA's Goddard Institute for Space Studies in New York, NY. The study appears in the November 16 issue of Journal of Geophysical Research - Atmospheres.
When Rind and his colleagues entered realistic estimates of freshwater from melting glaciers into their model, they found the North Atlantic circulation stopped completely after some 300 years. When the model was adjusted to make the circulation weaker than it is today, cessation of the Gulf Stream took only 150-200 years, matching current estimates based on paleo-climate records .
Freshwater additions into the ocean through the St. Lawrence River have a profound effect on the ocean circulation.
"The more freshwater you add, and the longer you add it, the greater reduction in the North Atlantic circulation," Rind said. "According to our model, this is a linear response."
When the Gulf Stream moves warm surface water from the equator north through the Atlantic, the water cools, gets saltier due to evaporation and becomes very dense. By the time it approaches the coast of Newfoundland, or further northeast in the Norwegian Sea, it becomes dense enough to sink. This process is called overturning. The dense water then slowly travels through the deep water southward into the Southern Hemisphere, with the return flow to the north occurring at the surface.
But when freshwater gets mixed with the salty water in the North Atlantic, it makes the water less dense and slows the overturning process and the ocean circulation.
While the study finds that freshwater input could slow and stop overturning, this would not stop the Gulf Stream entirely. That's because the stream is partially pushed by winds. As a result, the model shows the reduced Gulf Stream would only transport about half as much heat northward, thereby cooling Western Europe. Were this to occur in a global warming scenario, it would act to partly counter the effects of projected greenhouse warming in parts of Western Europe.
Many scientists suspect more rainfall in parts of the Northern Hemisphere during this century as a result of greenhouse warming. That's because warmer temperatures increase the atmosphere's capacity to carry water. "The North Atlantic circulation may already be weakening due to freshwater rainfall additions associated with global warming," Rind said.
But the model shows a number of inconsistencies with previous studies on the last ice age. Those studies speculate that once freshwater stopped flowing, the ocean circulation would return within only a few decades, matching a rapid warming seen in the climate record. The model finds that deepwater circulation does not return for at least hundreds of years when the freshwater additions end. Also contrary to observations, the model showed cooling throughout the Northern Hemisphere; during the last ice age, the majority of the United States land mass did not appear to cool.
"It's hard to understand how parts of the Northern Hemisphere might have cooled to the magnitude suggested, but not North America," Rind said. "That seems to imply that either the paleo-records are being misinterpreted, or something else went on, something major that is not being accounted for. This isn't necessarily the end of the story."
North Atlantic Ocean Circulation System
The North Atlantic Ocean circulation system is very sensitive to freshwater inputs. That's because the Gulf Stream moves warm surface water from the equator north through the Atlantic, where the water cools, gets saltier due to evaporation and becomes very dense. By the time it approaches the coast of Newfoundland, or further northeast in the Norwegian Sea, it becomes dense enough to sink. This process is called overturning. The dense water then slowly travels through the deep water southward into the Southern hemisphere, with the return flow to the North occurring at the surface. Today, the climate of Western Europe is much warmer than equivalent latitudes of North America, because the Gulf Stream provides a lot of warmth to those parts of Europe.
But when freshwater gets mixed into the salty water in the North Atlantic, it makes the water less dense and slows the overturning process and the ocean's circulation. The study finds that freshwater from melting glaciers on land that drained into the North Atlantic Ocean through the St. Lawrence River at the end of the last Ice Age, would have shut down the North Atlantic Deep Water circulation system in several hundred years. This is the circulation that drives the Gulf Stream. Also, the research indicates North Atlantic Deep Water circulation appears to respond linearly to freshwater additions-which means the more freshwater you add, and the longer you add it, the greater reduction in the North Atlantic circulation.
While the study finds that freshwater input could slow and stop overturning, this would not stop the Gulf Stream entirely. That's because the stream is partially pushed by winds. As a result, the computer model used by NASA's David Rind in his study shows the reduced Gulf Stream would only transport about half as much heat northward, thereby cooling Western Europe. Were this to occur in a global warming scenario, where rainfall increases in the Northern Hemisphere due to higher temperatures over the next century, it would act to partly counter the effects of projected greenhouse warming in parts of Western Europe. Credit: Deborah McLean, NASA Goddard Space Flight Center Multimedia Design Studio
The Gulf Stream (Conveyor Belt)
www.bbc.co.uk
The world's oceans move constantly. Ocean currents flow in complex patterns and are affected by the wind, the water's salinity and temperature, the shape of the ocean floor, and the earth's rotation.
How does it work?
The gulf stream is one of the strongest ocean currents in the world. It is driven by surface wind patterns and differences in water density. Surface water in the north Atlantic is cooled by winds from the Arctic. It becomes more salty and more dense and sinks to the ocean floor. The cold water then moves towards the equator where it will warm slowly. To replace the cold equator-bound water, the gulf stream moves warm water from the Gulf of Mexico north into the Atlantic.
The gulf stream brings warmth to the UK and north-west Europe and is the reason we have mild winters. The average annual temperature of north-west Europe is about 9C above the average for our latitude.
The past
At the end of the last Ice Age, when the ice sheet covering North America melted, the sudden increase in fresh water reduced the salinity of the north Atlantic surface water and therefore less 'dense water' sank and moved towards the equator. This reduced, or even shut-down completely, the warm gulf stream. Temperatures in north-west Europe fell by 5C in just a few decades
The present
Recent observations have shown that since 1950 there has been a decrease of 20% in the flow of cold water in the Faeroe Bank channel between Greenland and Scotland. This is one source of cold dense water that drives the density-based component of the gulf stream. There may be an increase in flow from other cold water sources, but, if not, it could be the start of the slow down of the gulf stream.
The future
Today, the Greenland ice sheet is more stable, but an increase in global temperatures (and therefore melting sea ice) and precipitation may add more fresh water to the north Atlantic, similar to what happened at the end of the last Ice Age.
Current climate models predict that if greenhouse gas emissions continue to increase, the component of the gulf stream driven by the differences in water density is likely to decrease by 25% in the next 100 years. As the gulf stream becomes weaker, it may become less stable and therefore be more likely to shut down completely in the future.
Implications
A reduced gulf stream would mean that less heat is brought to north-west Europe and therefore harsher winters. However, current climate model predictions are confident that the increase in temperatures resulting from an increase in greenhouse gas emissions is much greater than the potential cooling effect, so a cooling of the UK climate is unlikely this century.
Water:
Sea level rises
Glaciers and ice sheets
Flooding
http://www.bbc.co.uk/climate/impact/gulf_stream.shtml
The world's oceans move constantly. Ocean currents flow in complex patterns and are affected by the wind, the water's salinity and temperature, the shape of the ocean floor, and the earth's rotation.
How does it work?
The gulf stream is one of the strongest ocean currents in the world. It is driven by surface wind patterns and differences in water density. Surface water in the north Atlantic is cooled by winds from the Arctic. It becomes more salty and more dense and sinks to the ocean floor. The cold water then moves towards the equator where it will warm slowly. To replace the cold equator-bound water, the gulf stream moves warm water from the Gulf of Mexico north into the Atlantic.
The gulf stream brings warmth to the UK and north-west Europe and is the reason we have mild winters. The average annual temperature of north-west Europe is about 9C above the average for our latitude.
The past
At the end of the last Ice Age, when the ice sheet covering North America melted, the sudden increase in fresh water reduced the salinity of the north Atlantic surface water and therefore less 'dense water' sank and moved towards the equator. This reduced, or even shut-down completely, the warm gulf stream. Temperatures in north-west Europe fell by 5C in just a few decades
The present
Recent observations have shown that since 1950 there has been a decrease of 20% in the flow of cold water in the Faeroe Bank channel between Greenland and Scotland. This is one source of cold dense water that drives the density-based component of the gulf stream. There may be an increase in flow from other cold water sources, but, if not, it could be the start of the slow down of the gulf stream.
The future
Today, the Greenland ice sheet is more stable, but an increase in global temperatures (and therefore melting sea ice) and precipitation may add more fresh water to the north Atlantic, similar to what happened at the end of the last Ice Age.
Current climate models predict that if greenhouse gas emissions continue to increase, the component of the gulf stream driven by the differences in water density is likely to decrease by 25% in the next 100 years. As the gulf stream becomes weaker, it may become less stable and therefore be more likely to shut down completely in the future.
Implications
A reduced gulf stream would mean that less heat is brought to north-west Europe and therefore harsher winters. However, current climate model predictions are confident that the increase in temperatures resulting from an increase in greenhouse gas emissions is much greater than the potential cooling effect, so a cooling of the UK climate is unlikely this century.
Water:
Sea level rises
Glaciers and ice sheets
Flooding
http://www.bbc.co.uk/climate/impact/gulf_stream.shtml
The Science of Abrupt Climate Change: Should we be worried?
We generally consider climate changes as taking place on the scale of hundreds or even thousands of years. However, since the early 1990s, a radical shift in the scientific understanding of Earth's climate history has occurred. We now know that that major regional and global climate shifts have occurred in just a few decades or even a single year. The most recent of these shifts occurred just 8200 years ago. If an abrupt climate change of similar magnitude happened today, it would have severe consequences for humans and natural ecosystems. Although scientists consider an abrupt climate change unlikely in the next 100 years, their understanding of the phenomena is still a work-in-progress, and such a change could be triggered instantly by natural processes or by human-caused global warming with little warning.
The National Academy of Sciences--the board of scientists established by Congress in 1863 to advise the federal government on scientific matters--compiled a comprehensive report in 2002 entitled, Abrupt Climate Change: Inevitable Surprises. The 244-page report, which contains over 500 references, was written by a team of 59 of the top researchers in climate, and represents the most authoritative source of information about abrupt climate change available. Most of the material that follows was taken from this report.
The Greenland Ice Sheet: The Key to Understanding Earth's Climate Record
Ice cores hold an amazingly detailed record of Earth's climate. Each year, snow falling on glacial areas accumulates, piling on top of thousands of years of past snow, compressing the snow into yearly layers of ice, like rings inside a tree trunk. Preserved in the ice are tiny bubbles of ancient air that tell us the composition of the atmosphere at that time. The amount of dust in the snow tells us how windy the climate was. The thickness of the layer tells how much precipitation fell that year. Most importantly, the amount of the "heavy" isotope of oxygen, 18O, lets us infer the average atmospheric temperature, since water vapor with "heavy" 18O molecules condenses out of clouds more readily at cold temperatures.
Accessing this treasure-trove of climatic information is a huge undertaking--cores of ice must be drilled miles deep in some of the most inhospitable places on Earth. In 1989 the National Science Foundation funded the $25 million Greenland Ice Sheet Project II (GISP2) to drill an ice core through the entire two mile depth of the Greenland ice sheet. At the same time, a separate European project (GRIP), drilled through the ice just 20 miles away, providing a crucial independent check of the GISP2 data. By 1993, both the GRIP and GISP2 drills had hit bedrock, and two miles of ice cores, preserving 110,000 years of climate history in year-by-year layers, were taken to laboratories for analysis.
What the scientists found was surprising and unnerving. They had known from previous ice core and ocean sediment core data that Earth's climate had fluctuated significantly in the past. But what astonished them was the rapidity with which these changes occurred.
Ocean and lake sediment data from places such as California, Venezuela, and Antarctica have confirmed that these sudden climate changes affected not just Greenland, but the entire world. During the past 110,000 years, there have been at least 20 such abrupt climate changes. Only one period of stable climate has existed during the past 110,000 years--the 11,000 years of modern climate (the "Holocene" era). "Normal" climate for Earth is the climate of sudden extreme jumps--like a light switch flicking on and off.
Figure 1. Average Yearly Temperatures in Greenland over the past 100,000 Years as inferred from Oxygen isotope analysis of the GISP2 Greenland ice core.
Source: Cuffey, K.M., and G.D. Clow, "Temperature, accumulation, and ice sheet elevation in central Greenland throughout the last deglacial transition", Journal of Geophysical Research, 102, 383-396, 1997.
As seen in Figure 1, the ice core record showed frequent sudden warmings and coolings of 15° F (8°C) or more. Many of these changes happened in less than 10 years. In one case 11,600 years ago, when Earth emerged from the final phase of the most recent ice age (an event called the Younger Dryas), the Greenland ice core data showed that a 15°F (8°C) warming occurred in less than a decade, accompanied by a doubling of snow accumulation in 3 years. Most of this doubling occurred in a single year.
What causes abrupt climate change?
Current theories on the cause of abrupt climatic change focus on sudden shut downs and start-ups of the Meridional Overturning Circulation (MOC) (also referred to as the thermohaline circulation), which is a global network of density-driven ocean currents. The Meridional Overturning Circulation transports a tremendous amount of heat northward, keeping the North Atlantic and much of Europe up to 9�F (5�C) warmer, particularly in the winter. A sudden shut down of this current would have a ripple effect throughout the ocean-atmosphere system, forcing worldwide changes in ocean currents, and in the path of the atmospheric jet stream. Studies of North Atlantic Ocean sediments have revealed that the Meridional Overturning Circulation has shut down many times in the past, and that many of these shut downs coincide with the abrupt climate change events noted in the Greenland ice cores.
How does one shut down the Meridional Overturning Circulation ? First, one must examine the MOC itself. The MOC, or Great Ocean Conveyor Belt (Figure 2), is a system of interconnected ocean currents that girdle the planet.
At the surface, warmer ocean currents (shown here in orange) are driven by the winds, and so move parallel to the wind direction, except where continental land masses block the way. Water can also move vertically in the ocean. High density water sinks, and low density water rises. Salty water is more dense than fresh water, and cold water is more dense than warm water, so that wherever we find cold, salty water, it tends to sink. Colder currents (shown here in blue) are deeper and have higher salinity.
In the tropical Atlantic, the sun's heat evaporates large amounts of water, creating relatively warm, salty ocean water. This warm, salty water flows westward toward North America, then up the East Coast of the U.S., then northeastward toward Europe, forming the mighty Gulf Stream current. As this warm, salty water reaches the ocean regions on either side of Greenland, cold winds blowing off of Canada and Greenland cool the water substantially (in Figure 2, these regions are marked with white circles labeled, "Heat release to the atmosphere.") These cool, salty waters are now very dense compared to the surrounding waters, and sink to the bottom of the ocean. Thus, the oceanic areas by Greenland where this sinking occurs are called "deep-water formation areas". This North Atlantic deep water flows southward toward Antarctica, eventually making it all the way to the Pacific Ocean, where it rises back to the surface to complete the Great Ocean Conveyor Belt. It takes about 1000 years for the water to make a complete circuit around the globe.
Since the Great Ocean Conveyor Belt is driven in part by differences in ocean water density, if one can pump enough fresh water into the ocean in the key areas on either side of Greenland where the Gulf Stream waters cool and sink, this will lower the ocean's salinity (and therefore its density) enough so that the waters can no longer sink. As a result, the Atlantic conveyor belt and Gulf Stream current would shut down in just a few years, dramatically altering the climate.
How much fresh water is needed to shut down the MOC?
It is unknown precisely how much fresh water is needed to shut down the MOC. Scientists are fairly certain that the last two abrupt coolings seen the Greenland ice core, the "Younger Dryas" event and the "8200 years before present" event (Figure 1), both occurred when huge North American glacial melt-water lakes flooded down the St. Lawrence River into the North Atlantic when the ice dams restraining the lakes broke. The sudden addition of low-density fresh water presumably partially or totally stopped the sinking of ocean waters in the North Atlantic, slowing or completely stopping the Meridional Overturning Circulation. Once the fresh water got into the North Atlantic, it stayed, puddling on top of the ocean and freezing in winter. The Meridional Overturning Circulation stayed shut off for about 1100 years during the Younger Dryas event, then suddenly restarted, for reasons scientists don't understand. Current computer models of the climate cannot reproduce the observed sudden shut-down or start-up of the Meridional Overturning Circulation at the beginning and end of the Younger Dryas period.
Other sudden shut downs of the Meridional Overturning Circulation observed in ice core and ocean sediment records are not thought to be due to sudden melt-water floods into the North Atlantic. These events may have happened simply because Earth's climate system is chaotic, or perhaps because some critical threshold was crossed when increases in precipitation, river run-off, and ice melt put enough fresh water into the ocean to shut down the Meridional Overturning Circulation.
How likely is it that global warming will trigger abrupt climate change?
Global warming will increase precipitation, river run-off, melting of the Greenland ice sheet, and melting of polar sea ice, all of which will increase the amount of fresh water flowing into the critical deep-water formation areas by Greenland. In the 2007 IPCC Fourth Assessment Report Summary for Policymakers it states that, based on current model simulations, it is very likely (90-99% confidence) that the meridional overturning circulation (MOC) of the Atlantic Ocean will slow down during the 21st century. It also confirms the scientific consensus that is very unlikely the MOC will undergo a large abrupt transition during this century. Today's science is such that any long-term assessments of the MOC cannot be made with confidence.
How would the climate change if the Meridional overturning circulation shut down?
A shut down of the Meridional overturning circulation would suddenly decrease the amount of heat in the North Atlantic, leading to much colder temperatures in Europe and North America. A 2003 report prepared for the Department of Defense outlines what would happen if an abrupt climatic change similar to the 8200 years before present event were to recur today:
# Annual average temperatures would drop up to 5° F in North America, and up to 6° F in northern Europe. This is not sufficient to trigger an ice age, which requires about a 10° F drop in temperature world-wide, but could bring about conditions like experienced in 1816--the famed "year without a summer". In that year, volcanic ash from the mighty Tambora volcanic eruption in Indonesia blocked the sun's rays, significantly cooling the globe. Snow fell in New England in June, and killing frosts in July and August caused widespread crop failures and famine in New England and northern Europe.
# Annual average temperatures would warm up to 4° F in many areas of the Southern Hemisphere.
# Multi-year droughts in regions unaccustomed to drought would affect critical agricultural and water resource regions world-wide, greatly straining food and water supplies.
# Winter storms and winds would strengthen over North America and Europe.
Dr. Wally Broecker of Columbia University, the scientist who first pointed out the link between the Atlantic's conveyor circulation and abrupt climate change, wrote a letter in March 2004 to Science magazine, accusing the authors of the study of making exaggerated claims that "only intensify the existing polarization over global warming". Broecker argued that a global-warming induced abrupt climate change is not likely to occur until 100 years or so into the future, by which time Earth's temperature will have warmed sufficiently to offset much of the abrupt cooling a Meridional overturning circulation shut down would trigger. Broecker added: "What is needed is not more words but rather a means to shut down carbon dioxide emissions." The authors of the study defend their scenario thusly: "We have created a climate change scenario that although not the likely, is plausible, and would challenge United States national security in ways that should be considered immediately".
On the freezing of the UK and Europe
The possibility of the freezing of the UK and Europe will be determined by a "tug-of-war" of sorts, between the amount of greenhouse gases and the speed with which the MOC slows down. Greenhouse gases may have more of an impact than a slowing of the MOC, simply because they are more abundant today than ever in the earth's record. (CO2 levels were at 380 ppm as of 2007, and were never above 300 ppm during the 400,000 years studied in Antarctic ice cores).
Ocean experts see the MOC as having three levels: "faster", "slower", or "off." A 2005 comparison of eleven climate models showed that the MOC will likely be slowed by 10-50%, however, because the levels of carbon dioxide are so elevated, any cooling produced by the MOC slowing would be modest because the greenhouse gases would more than compensate. As a result, a net warming is still shown by these models for the UK and surrounding countries. Improving our measurements to monitor the MOC will allow for better predictions and reduce uncertainty of the amount of warming or cooling these areas of northern Europe will encounter.
What is being done about abrupt climate change?
The immediate obvious needs are for accurate, long-term measurements of the temperature, salinity, and flow rates of the major ocean currents in the North Atlantic Ocean. An expedition set sail from Great Britain on Feb. 13 2004, to provide just that. The voyage was part of a joint US/UK research project called Rapid Climate Change, which began in 2001. In the U.S., Senator Susan Collins (R-Maine) sponsored bill S.1164 to authorize $60 million for the National Oceanic and Atmospheric Administration (NOAA) to study abrupt climate change. On March 9, 2004, the Senate Commerce Committee approved the bill. It defines abrupt climate change as "a change in the climate that occurs so rapidly or unexpectedly that human or natural systems have difficulty adapting to the climate as changed." The bill would create a research program within NOAA's Office of Oceanic and Atmospheric Research to determine what causes sudden climate changes and using computer models to predict climate change events. This bill did not pass, and there is little chance for revival. The NTSC Joint Subcommittee On Ocean Science and Technology authored an Ocean Research Priorities Plan in January 2007, providing five key elements for reducing our vulnerability to abrupt climate change. These include: daily monitoring of ocean currents, temperature, and carbon, now-casting, model development, past-climate-change reconstructions, and additional climate-impact assessments.
Conclusion
The historical records shows us that abrupt climate change is not only possible--it is the normal state of affairs. The present warm, stable climate is a rare anomaly. It behooves us to learn as much as we can about the climate system so that we may be able to predict when the next abrupt shift in climate will come. Until we know better when this might happen, it would be wise to stop pouring so much carbon dioxide into the air. A nasty surprise might be lurking just around the corner. In the words of Dr. Wally Broecker, "the climate system is an angry beast, and we are poking it."
For further reading:
IPCC 4th Assessment, Chapter 5: Observations: Oceanic Climate Change and Sea Level 2007.
Who ya gonna call? RealClimate.org post by Gavin Schmidt and Michael Mann, August, 2007.
NASA's "A Chilling Possibility" press release, March 2004.
Abrupt Climate Change: Should we be worried?" Analysis by Woods Hole Oceanographical Institute, January 2003.
The Great Climate Flip-flop, a 1998 Atlantic Monthly article.
Abrupt climate change, a report prepared by Global Business Network (GBN) for the Department of Defense, October 2003.
The Two-Mile Time Machine : Ice Cores, Abrupt Climate Change, and Our Future, by Dr. Richard Alley, 2001. An excellent book on the Greenland ice cores findings.
The Day After Tomorrow: Could it really happen?
The National Academy of Sciences--the board of scientists established by Congress in 1863 to advise the federal government on scientific matters--compiled a comprehensive report in 2002 entitled, Abrupt Climate Change: Inevitable Surprises. The 244-page report, which contains over 500 references, was written by a team of 59 of the top researchers in climate, and represents the most authoritative source of information about abrupt climate change available. Most of the material that follows was taken from this report.
The Greenland Ice Sheet: The Key to Understanding Earth's Climate Record
Ice cores hold an amazingly detailed record of Earth's climate. Each year, snow falling on glacial areas accumulates, piling on top of thousands of years of past snow, compressing the snow into yearly layers of ice, like rings inside a tree trunk. Preserved in the ice are tiny bubbles of ancient air that tell us the composition of the atmosphere at that time. The amount of dust in the snow tells us how windy the climate was. The thickness of the layer tells how much precipitation fell that year. Most importantly, the amount of the "heavy" isotope of oxygen, 18O, lets us infer the average atmospheric temperature, since water vapor with "heavy" 18O molecules condenses out of clouds more readily at cold temperatures.
Accessing this treasure-trove of climatic information is a huge undertaking--cores of ice must be drilled miles deep in some of the most inhospitable places on Earth. In 1989 the National Science Foundation funded the $25 million Greenland Ice Sheet Project II (GISP2) to drill an ice core through the entire two mile depth of the Greenland ice sheet. At the same time, a separate European project (GRIP), drilled through the ice just 20 miles away, providing a crucial independent check of the GISP2 data. By 1993, both the GRIP and GISP2 drills had hit bedrock, and two miles of ice cores, preserving 110,000 years of climate history in year-by-year layers, were taken to laboratories for analysis.
What the scientists found was surprising and unnerving. They had known from previous ice core and ocean sediment core data that Earth's climate had fluctuated significantly in the past. But what astonished them was the rapidity with which these changes occurred.
Ocean and lake sediment data from places such as California, Venezuela, and Antarctica have confirmed that these sudden climate changes affected not just Greenland, but the entire world. During the past 110,000 years, there have been at least 20 such abrupt climate changes. Only one period of stable climate has existed during the past 110,000 years--the 11,000 years of modern climate (the "Holocene" era). "Normal" climate for Earth is the climate of sudden extreme jumps--like a light switch flicking on and off.
Figure 1. Average Yearly Temperatures in Greenland over the past 100,000 Years as inferred from Oxygen isotope analysis of the GISP2 Greenland ice core.
Source: Cuffey, K.M., and G.D. Clow, "Temperature, accumulation, and ice sheet elevation in central Greenland throughout the last deglacial transition", Journal of Geophysical Research, 102, 383-396, 1997.
As seen in Figure 1, the ice core record showed frequent sudden warmings and coolings of 15° F (8°C) or more. Many of these changes happened in less than 10 years. In one case 11,600 years ago, when Earth emerged from the final phase of the most recent ice age (an event called the Younger Dryas), the Greenland ice core data showed that a 15°F (8°C) warming occurred in less than a decade, accompanied by a doubling of snow accumulation in 3 years. Most of this doubling occurred in a single year.
What causes abrupt climate change?
Current theories on the cause of abrupt climatic change focus on sudden shut downs and start-ups of the Meridional Overturning Circulation (MOC) (also referred to as the thermohaline circulation), which is a global network of density-driven ocean currents. The Meridional Overturning Circulation transports a tremendous amount of heat northward, keeping the North Atlantic and much of Europe up to 9�F (5�C) warmer, particularly in the winter. A sudden shut down of this current would have a ripple effect throughout the ocean-atmosphere system, forcing worldwide changes in ocean currents, and in the path of the atmospheric jet stream. Studies of North Atlantic Ocean sediments have revealed that the Meridional Overturning Circulation has shut down many times in the past, and that many of these shut downs coincide with the abrupt climate change events noted in the Greenland ice cores.
How does one shut down the Meridional Overturning Circulation ? First, one must examine the MOC itself. The MOC, or Great Ocean Conveyor Belt (Figure 2), is a system of interconnected ocean currents that girdle the planet.
At the surface, warmer ocean currents (shown here in orange) are driven by the winds, and so move parallel to the wind direction, except where continental land masses block the way. Water can also move vertically in the ocean. High density water sinks, and low density water rises. Salty water is more dense than fresh water, and cold water is more dense than warm water, so that wherever we find cold, salty water, it tends to sink. Colder currents (shown here in blue) are deeper and have higher salinity.
In the tropical Atlantic, the sun's heat evaporates large amounts of water, creating relatively warm, salty ocean water. This warm, salty water flows westward toward North America, then up the East Coast of the U.S., then northeastward toward Europe, forming the mighty Gulf Stream current. As this warm, salty water reaches the ocean regions on either side of Greenland, cold winds blowing off of Canada and Greenland cool the water substantially (in Figure 2, these regions are marked with white circles labeled, "Heat release to the atmosphere.") These cool, salty waters are now very dense compared to the surrounding waters, and sink to the bottom of the ocean. Thus, the oceanic areas by Greenland where this sinking occurs are called "deep-water formation areas". This North Atlantic deep water flows southward toward Antarctica, eventually making it all the way to the Pacific Ocean, where it rises back to the surface to complete the Great Ocean Conveyor Belt. It takes about 1000 years for the water to make a complete circuit around the globe.
Since the Great Ocean Conveyor Belt is driven in part by differences in ocean water density, if one can pump enough fresh water into the ocean in the key areas on either side of Greenland where the Gulf Stream waters cool and sink, this will lower the ocean's salinity (and therefore its density) enough so that the waters can no longer sink. As a result, the Atlantic conveyor belt and Gulf Stream current would shut down in just a few years, dramatically altering the climate.
How much fresh water is needed to shut down the MOC?
It is unknown precisely how much fresh water is needed to shut down the MOC. Scientists are fairly certain that the last two abrupt coolings seen the Greenland ice core, the "Younger Dryas" event and the "8200 years before present" event (Figure 1), both occurred when huge North American glacial melt-water lakes flooded down the St. Lawrence River into the North Atlantic when the ice dams restraining the lakes broke. The sudden addition of low-density fresh water presumably partially or totally stopped the sinking of ocean waters in the North Atlantic, slowing or completely stopping the Meridional Overturning Circulation. Once the fresh water got into the North Atlantic, it stayed, puddling on top of the ocean and freezing in winter. The Meridional Overturning Circulation stayed shut off for about 1100 years during the Younger Dryas event, then suddenly restarted, for reasons scientists don't understand. Current computer models of the climate cannot reproduce the observed sudden shut-down or start-up of the Meridional Overturning Circulation at the beginning and end of the Younger Dryas period.
Other sudden shut downs of the Meridional Overturning Circulation observed in ice core and ocean sediment records are not thought to be due to sudden melt-water floods into the North Atlantic. These events may have happened simply because Earth's climate system is chaotic, or perhaps because some critical threshold was crossed when increases in precipitation, river run-off, and ice melt put enough fresh water into the ocean to shut down the Meridional Overturning Circulation.
How likely is it that global warming will trigger abrupt climate change?
Global warming will increase precipitation, river run-off, melting of the Greenland ice sheet, and melting of polar sea ice, all of which will increase the amount of fresh water flowing into the critical deep-water formation areas by Greenland. In the 2007 IPCC Fourth Assessment Report Summary for Policymakers it states that, based on current model simulations, it is very likely (90-99% confidence) that the meridional overturning circulation (MOC) of the Atlantic Ocean will slow down during the 21st century. It also confirms the scientific consensus that is very unlikely the MOC will undergo a large abrupt transition during this century. Today's science is such that any long-term assessments of the MOC cannot be made with confidence.
How would the climate change if the Meridional overturning circulation shut down?
A shut down of the Meridional overturning circulation would suddenly decrease the amount of heat in the North Atlantic, leading to much colder temperatures in Europe and North America. A 2003 report prepared for the Department of Defense outlines what would happen if an abrupt climatic change similar to the 8200 years before present event were to recur today:
# Annual average temperatures would drop up to 5° F in North America, and up to 6° F in northern Europe. This is not sufficient to trigger an ice age, which requires about a 10° F drop in temperature world-wide, but could bring about conditions like experienced in 1816--the famed "year without a summer". In that year, volcanic ash from the mighty Tambora volcanic eruption in Indonesia blocked the sun's rays, significantly cooling the globe. Snow fell in New England in June, and killing frosts in July and August caused widespread crop failures and famine in New England and northern Europe.
# Annual average temperatures would warm up to 4° F in many areas of the Southern Hemisphere.
# Multi-year droughts in regions unaccustomed to drought would affect critical agricultural and water resource regions world-wide, greatly straining food and water supplies.
# Winter storms and winds would strengthen over North America and Europe.
Dr. Wally Broecker of Columbia University, the scientist who first pointed out the link between the Atlantic's conveyor circulation and abrupt climate change, wrote a letter in March 2004 to Science magazine, accusing the authors of the study of making exaggerated claims that "only intensify the existing polarization over global warming". Broecker argued that a global-warming induced abrupt climate change is not likely to occur until 100 years or so into the future, by which time Earth's temperature will have warmed sufficiently to offset much of the abrupt cooling a Meridional overturning circulation shut down would trigger. Broecker added: "What is needed is not more words but rather a means to shut down carbon dioxide emissions." The authors of the study defend their scenario thusly: "We have created a climate change scenario that although not the likely, is plausible, and would challenge United States national security in ways that should be considered immediately".
On the freezing of the UK and Europe
The possibility of the freezing of the UK and Europe will be determined by a "tug-of-war" of sorts, between the amount of greenhouse gases and the speed with which the MOC slows down. Greenhouse gases may have more of an impact than a slowing of the MOC, simply because they are more abundant today than ever in the earth's record. (CO2 levels were at 380 ppm as of 2007, and were never above 300 ppm during the 400,000 years studied in Antarctic ice cores).
Ocean experts see the MOC as having three levels: "faster", "slower", or "off." A 2005 comparison of eleven climate models showed that the MOC will likely be slowed by 10-50%, however, because the levels of carbon dioxide are so elevated, any cooling produced by the MOC slowing would be modest because the greenhouse gases would more than compensate. As a result, a net warming is still shown by these models for the UK and surrounding countries. Improving our measurements to monitor the MOC will allow for better predictions and reduce uncertainty of the amount of warming or cooling these areas of northern Europe will encounter.
What is being done about abrupt climate change?
The immediate obvious needs are for accurate, long-term measurements of the temperature, salinity, and flow rates of the major ocean currents in the North Atlantic Ocean. An expedition set sail from Great Britain on Feb. 13 2004, to provide just that. The voyage was part of a joint US/UK research project called Rapid Climate Change, which began in 2001. In the U.S., Senator Susan Collins (R-Maine) sponsored bill S.1164 to authorize $60 million for the National Oceanic and Atmospheric Administration (NOAA) to study abrupt climate change. On March 9, 2004, the Senate Commerce Committee approved the bill. It defines abrupt climate change as "a change in the climate that occurs so rapidly or unexpectedly that human or natural systems have difficulty adapting to the climate as changed." The bill would create a research program within NOAA's Office of Oceanic and Atmospheric Research to determine what causes sudden climate changes and using computer models to predict climate change events. This bill did not pass, and there is little chance for revival. The NTSC Joint Subcommittee On Ocean Science and Technology authored an Ocean Research Priorities Plan in January 2007, providing five key elements for reducing our vulnerability to abrupt climate change. These include: daily monitoring of ocean currents, temperature, and carbon, now-casting, model development, past-climate-change reconstructions, and additional climate-impact assessments.
Conclusion
The historical records shows us that abrupt climate change is not only possible--it is the normal state of affairs. The present warm, stable climate is a rare anomaly. It behooves us to learn as much as we can about the climate system so that we may be able to predict when the next abrupt shift in climate will come. Until we know better when this might happen, it would be wise to stop pouring so much carbon dioxide into the air. A nasty surprise might be lurking just around the corner. In the words of Dr. Wally Broecker, "the climate system is an angry beast, and we are poking it."
For further reading:
IPCC 4th Assessment, Chapter 5: Observations: Oceanic Climate Change and Sea Level 2007.
Who ya gonna call? RealClimate.org post by Gavin Schmidt and Michael Mann, August, 2007.
NASA's "A Chilling Possibility" press release, March 2004.
Abrupt Climate Change: Should we be worried?" Analysis by Woods Hole Oceanographical Institute, January 2003.
The Great Climate Flip-flop, a 1998 Atlantic Monthly article.
Abrupt climate change, a report prepared by Global Business Network (GBN) for the Department of Defense, October 2003.
The Two-Mile Time Machine : Ice Cores, Abrupt Climate Change, and Our Future, by Dr. Richard Alley, 2001. An excellent book on the Greenland ice cores findings.
The Day After Tomorrow: Could it really happen?
Thermal Conductivity
In physics, thermal conductivity, k, is the property of a material that indicates its ability to conduct heat. It appears primarily in Fourier's Law for heat conduction.
First, we define heat conduction by the formula:
H=\frac{\Delta Q}{\Delta t}=k\times A\times\frac{\Delta T}{x}
where \frac{\Delta Q}{\Delta t} is the rate of heat flow, k is the thermal conductivity, A is the total surface area of conducting surface, ΔT is temperature difference and x is the thickness of conducting surface separating the 2 temperatures.
Thus, rearranging the equation gives thermal conductivity,
k=\frac{\Delta Q}{\Delta t}\times\frac{1}{A}\times\frac{x}{\Delta T}
(Note: \frac{\Delta T}{x} is the temperature gradient)
In other words, it is defined as the quantity of heat, ΔQ, transmitted during time Δt through a thickness x, in a direction normal to a surface of area A, due to a temperature difference ΔT, under steady state conditions and when the heat transfer is dependent only on the temperature gradient.
Alternately, it can be thought of as a flux of heat (energy per unit area per unit time) divided by a temperature gradient (temperature difference per unit length)
k=\frac{\Delta Q}{A\times{} \Delta t}\times\frac{x}{\Delta T}
Typical units are SI: W/(m·K) and English units: Btu·ft/(h·ft²·°F). To convert between the two, use the relation 1 Btu·ft/(h·ft²·°F) = 1.730735 W/(m·K). [Perry's Chemical Engineers' Handbook, 7th Edition, Table 1-4]
Examples
In metals, thermal conductivity approximately tracks electrical conductivity according to the Wiedemann-Franz law, as freely moving valence electrons transfer not only electric current but also heat energy. However, the general correlation between electrical and thermal conductance does not hold for other materials, due to the increased importance of phonon carriers for heat in non-metals. As shown in the table below, highly electrically conductive silver is less thermally conductive than diamond, which is an electrical insulator.
Thermal conductivity depends on many properties of a material, notably its structure and temperature. For instance, pure crystalline substances exhibit very different thermal conductivities along different crystal axes, due to differences in phonon coupling along a given crystal axis. Sapphire is a notable example of variable thermal conductivity based on orientation and temperature, for which the CRC Handbook reports a thermal conductivity of 2.6 W/(m·K) perpendicular to the c-axis at 373 K, but 6000 W/(m·K) at 36 degrees from the c-axis and 35 K.
Air and other gases are generally good insulators, in the absence of convection. Therefore, many insulating materials function simply by having a large number of gas-filled pockets which prevent large-scale convection. Examples of these include expanded and extruded polystyrene (popularly referred to as "styrofoam") and silica aerogel. Natural, biological insulators such as fur and feathers achieve similar effects by dramatically inhibiting convection of air or water near an animal's skin.
Thermal conductivity is important in building insulation and related fields. However, materials used in such trades are rarely subjected to chemical purity standards. Several construction materials' k values are listed below. These should be considered approximate due to the uncertainties related to material definitions.
The following table is meant as a small sample of data to illustrate the thermal conductivity of various types of substances. For more complete listings of measured k-values, see the references.
[edit] List of thermal conductivities
Main article: List of thermal conductivities
This is a list of approximate values of thermal conductivity, k, for some common materials. Please consult the list of thermal conductivities for more accurate values, references and detailed information.
Material ↓ Thermal conductivity
W/(m·K) ↓
Cement, Portland [1] 0.29
Concrete, stone [1] 1.7
Air 0.025
Wood 0.04 - 0.4
Alcohols and oils 0.1 - 0.21
Silica Aerogel 0.004-0.03
Soil 1.5
Rubber 0.16
Epoxy (unfilled) 0.19
Hydro-NM-Oxide (Nansulate) 0.018
LPG 0.23 - 0.26
Epoxy (silica-filled) 0.30
Water (liquid) 0.6
Thermal grease 0.7 - 3
Thermal epoxy 1 - 7
Glass 1.1
Ice 2
Sandstone 2.4
Stainless steel[2] 12.11 ~ 45.0
Lead 35.3
Aluminium 237
Gold 318
Copper 401
Silver 429
Diamond 900 - 2320
[edit] Measurement
Main article: Thermal conductivity measurement
Generally speaking, there are a number of possibilities to measure thermal conductivity, each of them suitable for a limited range of materials, depending on the thermal properties and the medium temperature. There can be made a distinction between steady-state and transient techniques.
In general the steady-state techniques perform a measurement when the temperature of the material that is measured does not change with time. This makes the signal analysis straight forward (steady state implies constant signals). The disadvantage generally is that it takes a well-engineered experimental setup. The Divided Bar (various types) is the most common device used for consolidated rock samples.
The transient techniques perform a measurement during the process of heating up. The advantage is that measurements can be made relatively quickly. Transient methods are usually carried out by needle probes (inserted into samples or plunged into the ocean floor).
For good conductors of heat, Searle's bar method can be used.[1] For poor conductors of heat, Lee's disc method can be used.[2] An alternative traditional method using real thermometers is described at [3]. A brief review of new methods measuring thermal conductivity, thermal diffusivity and specific heat within a single measurement is available at [4]. A thermal conductance tester, one of the instruments of gemology, determines if gems are genuine diamonds using diamond's uniquely high thermal conductivity.
[edit] Standard Measurement Techniques
* IEEE Standard 442-1981, "IEEE guide for soil thermal resistivity measurements" see als soil thermal properties [5]
* IEEE Standard 98-2002, "Standard for the Preparation of Test Procedures for the Thermal Evaluation of Solid Electrical Insulating Materials", ISBN 0-7381-3277-2 [6]
* ASTM Standard D5470-06, "Standard Test Method for Thermal Transmission Properties of Thermally Conductive Electrical Insulation Materials" [7]
* ASTM Standard E1225-04, "Standard Test Method for Thermal Conductivity of Solids by Means of the Guarded-Comparative-Longitudinal Heat Flow Technique" [8]
* ASTM Standard D5930-01, "Standard Test Method for Thermal Conductivity of Plastics by Means of a Transient Line-Source Technique" [9]
* ASTM Standard D2717-95, "Standard Test Method for Thermal Conductivity of Liquids" [10]
[edit] Difference between US and European notation
What is called the k-value of construction materials (e.g. window glass) in the US, is called λ-value in Europe.
What is called U-value (= the inverse of R-value) in the US, used to be called k-value in Europe, but is now also called U-value in Europe.
K-value (with capital k) refers in Europe to the total isolation value of a building. K-value is obtained by multiplying the form factor of the building (= the total inward surface of the outward walls of the building divided by the total volume of the building) with the average U-value of the outward walls of the building. K-value is therefore expressed as (m2.m-3).(W.K-1.m-2) = W.K-1.m-3. A house with a volume of 400 m³ and a K-value of 0.45 (the new European norm. It is commonly referred to as K45) will therefore theoretically require 180 W to maintain its interior temperature 1 degree K above exterior temperature. So, to maintain the house at 20°C when it is freezing outside (0°C), 3600 W of continuous heating is required.
[edit] Related terms
The reciprocal of thermal conductivity is thermal resistivity, measured in kelvin-metres per watt (K·m·W−1).
When dealing with a known amount of material, its thermal conductance and the reciprocal property, thermal resistance, can be described. Unfortunately there are differing definitions for these terms.
[edit] Thermal Conductance
For general scientific use, thermal conductance is the quantity of heat that passes in unit time through a plate of particular area and thickness when its opposite faces differ in temperature by one degree. For a plate of thermal conductivity k, area A and thickness L this is kA/L, measured in W·K−1 (equivalent to: W/°C). Thermal conductivity and conductance are analogous to electrical conductivity (A·m−1·V−1) and electrical conductance (A·V−1).
There is also a measure known as heat transfer coefficient: the quantity of heat that passes in unit time through unit area of a plate of particular thickness when its opposite faces differ in temperature by one degree. The reciprocal is thermal insulance. In summary:
* thermal conductance = kA/L, measured in W·K−1
o thermal resistance = L/kA, measured in K·W−1 (equivalent to: °C/W)
* heat transfer coefficient = k/L, measured in W·K−1·m−2
o thermal insulance = L/k, measured in K·m²·W−1.
The heat transfer coefficient is also known as thermal admittance
[edit] Thermal Resistance
When thermal resistances occur in series, they are additive. So when heat flows through two components each with a resistance of 1 °C/W, the total resistance is 2 °C/W.
A common engineering design problem involves the selection of an appropriate sized heat sink for a given heat source. Working in units of thermal resistance greatly simplifies the design calculation. The following formula can be used to estimate the performance:
R_{hs} = \frac {\Delta T}{P_{th}} - R_s
where:
* Rhs is the maximum thermal resistance of the heat sink to ambient, in °C/W
* ΔT is the temperature difference (temperature drop), in °C
* Pth is the thermal power (heat flow), in Watts
* Rs is the thermal resistance of the heat source, in °C/W
For example, if a component produces 100 W of heat, and has a thermal resistance of 0.5 °C/W, what is the maximum thermal resistance of the heat sink? Suppose the maximum temperature is 125 °C, and the ambient temperature is 25 °C; then the ΔT is 100 °C. The heat sink's thermal resistance to ambient must then be 0.5 °C/W or less.
[edit] Alternate definition (buildings)
When dealing with buildings, thermal resistance or R-value means what is described above as thermal insulance, and thermal conductance means the reciprocal. For materials in series, these thermal resistances (unlike conductances) can simply be added to give a thermal resistance for the whole.
A third term, thermal transmittance, incorporates the thermal conductance of a structure along with heat transfer due to convection and radiation. It is measured in the same units as thermal conductance and is sometimes known as the composite thermal conductance. The term U-value is another synonym.
In summary, for a plate of thermal conductivity k (the k value [3]), area A and thickness L:
* thermal conductance = k/L, measured in W·K−1·m−2;
* thermal resistance (R value) = L/k, measured in K·m²·W−1;
* thermal transmittance (U value) = 1/(Σ(L/k)) + convection + radiation, measured in W·K−1·m−2.
[edit] Textile industry
In textiles, a tog value may be quoted as a measure of thermal resistance in place of a measure in SI units.
[edit] Origins
The thermal conductivity of a system is determined by how atoms comprising the system interact. There are no simple, correct expressions for thermal conductivity. There are two different approaches for calculating the thermal conductivity of a system.
The first approach employs the Green-Kubo relations. Although this employs analytic expressions which in principle can be solved, in order to calculate the thermal conductivity of a dense fluid or solid using this relation requires the use of molecular dynamics computer simulation.
The second approach is based upon the relaxation time approach. Due to the anharmonicity within the crystal potential, the phonons in the system are known to scatter. There are three main mechanisms for scattering:
* Boundary scattering, a phonon hitting the boundary of a system;
* Mass defect scattering, a phonon hitting an impurity within the system and scattering;
* Phonon-phonon scattering, a phonon breaking into two lower energy phonons or a phonon colliding with another phonon and merging into one higher energy phonon.
Further information can be found in the publication "The Physics of Phonons" by G P Srivastava.
[edit] See also
* Heat conduction
* Heat transfer
* Heat transfer mechanisms
* Insulated pipes
* R-value
* Specific Heat
* Thermal bridge
* Thermal contact conductance
* Thermal diffusivity
* Thermal resistance in electronics
* Thermistor
* Thermocouple
* Electrical conductivity
[edit] External links
* Table with the Thermal Conductivity of the Elements
* http://physics.nist.gov/Pubs/SP811/appenB9.html
* http://www.npl.co.uk/thermal/faq_index.html#heat%20transfer%20property thermophysics FAQ5
* http://www.ornl.gov/roofs+walls/research/detailed_papers/rastra/dynamic.htm
* http://www.tak2000.com/data2.htm
* http://thermophys.savba.sk
* Calculation of the Thermal Conductivity of Glass Calculation of the Thermal Conductivity of Glass at Room Temperature from the Chemical Composition
* http://www.mathisinstruments.com/index.asp?pathinfo=/html/content/technology/tech_glossary.asp&dbbypass=
* Viscosity and Thermal Conductivity Equations for Nitrogen, Oxygen, Argon, and Air
[edit] References
1. ^ a b Thermal Conductivity of some common Materials
2. ^ Thermal Conductivity of Metals
3. ^ Definition of k value from Plastics New Zealand
* Callister, William (2003). "Appendix B", Materials Science and Engineering - An Introduction. John Wiley & Sons, INC, 757. ISBN 0-471-22471-5.
* Halliday, David; Resnick, Robert; & Walker, Jearl(1997). Fundamentals of Physics (5th ed.). John Wiley and Sons, INC., NY ISBN 0-471-10558-9.
* TM 5-852-6 AFR 88-19, Volume 6 (Army Corp of Engineers publication)
* Srivastava G. P (1990), "The Physics of Phonons." Adam Hilger, IOP Publishing Ltd, Bristol.
LEARN DESK
Thermal Conductivity - http://en.wikipedia.org/wiki/Thermal_conductivity
Heat Conductivity - http://en.wikipedia.org/wiki/Heat_conduction
First, we define heat conduction by the formula:
H=\frac{\Delta Q}{\Delta t}=k\times A\times\frac{\Delta T}{x}
where \frac{\Delta Q}{\Delta t} is the rate of heat flow, k is the thermal conductivity, A is the total surface area of conducting surface, ΔT is temperature difference and x is the thickness of conducting surface separating the 2 temperatures.
Thus, rearranging the equation gives thermal conductivity,
k=\frac{\Delta Q}{\Delta t}\times\frac{1}{A}\times\frac{x}{\Delta T}
(Note: \frac{\Delta T}{x} is the temperature gradient)
In other words, it is defined as the quantity of heat, ΔQ, transmitted during time Δt through a thickness x, in a direction normal to a surface of area A, due to a temperature difference ΔT, under steady state conditions and when the heat transfer is dependent only on the temperature gradient.
Alternately, it can be thought of as a flux of heat (energy per unit area per unit time) divided by a temperature gradient (temperature difference per unit length)
k=\frac{\Delta Q}{A\times{} \Delta t}\times\frac{x}{\Delta T}
Typical units are SI: W/(m·K) and English units: Btu·ft/(h·ft²·°F). To convert between the two, use the relation 1 Btu·ft/(h·ft²·°F) = 1.730735 W/(m·K). [Perry's Chemical Engineers' Handbook, 7th Edition, Table 1-4]
Examples
In metals, thermal conductivity approximately tracks electrical conductivity according to the Wiedemann-Franz law, as freely moving valence electrons transfer not only electric current but also heat energy. However, the general correlation between electrical and thermal conductance does not hold for other materials, due to the increased importance of phonon carriers for heat in non-metals. As shown in the table below, highly electrically conductive silver is less thermally conductive than diamond, which is an electrical insulator.
Thermal conductivity depends on many properties of a material, notably its structure and temperature. For instance, pure crystalline substances exhibit very different thermal conductivities along different crystal axes, due to differences in phonon coupling along a given crystal axis. Sapphire is a notable example of variable thermal conductivity based on orientation and temperature, for which the CRC Handbook reports a thermal conductivity of 2.6 W/(m·K) perpendicular to the c-axis at 373 K, but 6000 W/(m·K) at 36 degrees from the c-axis and 35 K.
Air and other gases are generally good insulators, in the absence of convection. Therefore, many insulating materials function simply by having a large number of gas-filled pockets which prevent large-scale convection. Examples of these include expanded and extruded polystyrene (popularly referred to as "styrofoam") and silica aerogel. Natural, biological insulators such as fur and feathers achieve similar effects by dramatically inhibiting convection of air or water near an animal's skin.
Thermal conductivity is important in building insulation and related fields. However, materials used in such trades are rarely subjected to chemical purity standards. Several construction materials' k values are listed below. These should be considered approximate due to the uncertainties related to material definitions.
The following table is meant as a small sample of data to illustrate the thermal conductivity of various types of substances. For more complete listings of measured k-values, see the references.
[edit] List of thermal conductivities
Main article: List of thermal conductivities
This is a list of approximate values of thermal conductivity, k, for some common materials. Please consult the list of thermal conductivities for more accurate values, references and detailed information.
Material ↓ Thermal conductivity
W/(m·K) ↓
Cement, Portland [1] 0.29
Concrete, stone [1] 1.7
Air 0.025
Wood 0.04 - 0.4
Alcohols and oils 0.1 - 0.21
Silica Aerogel 0.004-0.03
Soil 1.5
Rubber 0.16
Epoxy (unfilled) 0.19
Hydro-NM-Oxide (Nansulate) 0.018
LPG 0.23 - 0.26
Epoxy (silica-filled) 0.30
Water (liquid) 0.6
Thermal grease 0.7 - 3
Thermal epoxy 1 - 7
Glass 1.1
Ice 2
Sandstone 2.4
Stainless steel[2] 12.11 ~ 45.0
Lead 35.3
Aluminium 237
Gold 318
Copper 401
Silver 429
Diamond 900 - 2320
[edit] Measurement
Main article: Thermal conductivity measurement
Generally speaking, there are a number of possibilities to measure thermal conductivity, each of them suitable for a limited range of materials, depending on the thermal properties and the medium temperature. There can be made a distinction between steady-state and transient techniques.
In general the steady-state techniques perform a measurement when the temperature of the material that is measured does not change with time. This makes the signal analysis straight forward (steady state implies constant signals). The disadvantage generally is that it takes a well-engineered experimental setup. The Divided Bar (various types) is the most common device used for consolidated rock samples.
The transient techniques perform a measurement during the process of heating up. The advantage is that measurements can be made relatively quickly. Transient methods are usually carried out by needle probes (inserted into samples or plunged into the ocean floor).
For good conductors of heat, Searle's bar method can be used.[1] For poor conductors of heat, Lee's disc method can be used.[2] An alternative traditional method using real thermometers is described at [3]. A brief review of new methods measuring thermal conductivity, thermal diffusivity and specific heat within a single measurement is available at [4]. A thermal conductance tester, one of the instruments of gemology, determines if gems are genuine diamonds using diamond's uniquely high thermal conductivity.
[edit] Standard Measurement Techniques
* IEEE Standard 442-1981, "IEEE guide for soil thermal resistivity measurements" see als soil thermal properties [5]
* IEEE Standard 98-2002, "Standard for the Preparation of Test Procedures for the Thermal Evaluation of Solid Electrical Insulating Materials", ISBN 0-7381-3277-2 [6]
* ASTM Standard D5470-06, "Standard Test Method for Thermal Transmission Properties of Thermally Conductive Electrical Insulation Materials" [7]
* ASTM Standard E1225-04, "Standard Test Method for Thermal Conductivity of Solids by Means of the Guarded-Comparative-Longitudinal Heat Flow Technique" [8]
* ASTM Standard D5930-01, "Standard Test Method for Thermal Conductivity of Plastics by Means of a Transient Line-Source Technique" [9]
* ASTM Standard D2717-95, "Standard Test Method for Thermal Conductivity of Liquids" [10]
[edit] Difference between US and European notation
What is called the k-value of construction materials (e.g. window glass) in the US, is called λ-value in Europe.
What is called U-value (= the inverse of R-value) in the US, used to be called k-value in Europe, but is now also called U-value in Europe.
K-value (with capital k) refers in Europe to the total isolation value of a building. K-value is obtained by multiplying the form factor of the building (= the total inward surface of the outward walls of the building divided by the total volume of the building) with the average U-value of the outward walls of the building. K-value is therefore expressed as (m2.m-3).(W.K-1.m-2) = W.K-1.m-3. A house with a volume of 400 m³ and a K-value of 0.45 (the new European norm. It is commonly referred to as K45) will therefore theoretically require 180 W to maintain its interior temperature 1 degree K above exterior temperature. So, to maintain the house at 20°C when it is freezing outside (0°C), 3600 W of continuous heating is required.
[edit] Related terms
The reciprocal of thermal conductivity is thermal resistivity, measured in kelvin-metres per watt (K·m·W−1).
When dealing with a known amount of material, its thermal conductance and the reciprocal property, thermal resistance, can be described. Unfortunately there are differing definitions for these terms.
[edit] Thermal Conductance
For general scientific use, thermal conductance is the quantity of heat that passes in unit time through a plate of particular area and thickness when its opposite faces differ in temperature by one degree. For a plate of thermal conductivity k, area A and thickness L this is kA/L, measured in W·K−1 (equivalent to: W/°C). Thermal conductivity and conductance are analogous to electrical conductivity (A·m−1·V−1) and electrical conductance (A·V−1).
There is also a measure known as heat transfer coefficient: the quantity of heat that passes in unit time through unit area of a plate of particular thickness when its opposite faces differ in temperature by one degree. The reciprocal is thermal insulance. In summary:
* thermal conductance = kA/L, measured in W·K−1
o thermal resistance = L/kA, measured in K·W−1 (equivalent to: °C/W)
* heat transfer coefficient = k/L, measured in W·K−1·m−2
o thermal insulance = L/k, measured in K·m²·W−1.
The heat transfer coefficient is also known as thermal admittance
[edit] Thermal Resistance
When thermal resistances occur in series, they are additive. So when heat flows through two components each with a resistance of 1 °C/W, the total resistance is 2 °C/W.
A common engineering design problem involves the selection of an appropriate sized heat sink for a given heat source. Working in units of thermal resistance greatly simplifies the design calculation. The following formula can be used to estimate the performance:
R_{hs} = \frac {\Delta T}{P_{th}} - R_s
where:
* Rhs is the maximum thermal resistance of the heat sink to ambient, in °C/W
* ΔT is the temperature difference (temperature drop), in °C
* Pth is the thermal power (heat flow), in Watts
* Rs is the thermal resistance of the heat source, in °C/W
For example, if a component produces 100 W of heat, and has a thermal resistance of 0.5 °C/W, what is the maximum thermal resistance of the heat sink? Suppose the maximum temperature is 125 °C, and the ambient temperature is 25 °C; then the ΔT is 100 °C. The heat sink's thermal resistance to ambient must then be 0.5 °C/W or less.
[edit] Alternate definition (buildings)
When dealing with buildings, thermal resistance or R-value means what is described above as thermal insulance, and thermal conductance means the reciprocal. For materials in series, these thermal resistances (unlike conductances) can simply be added to give a thermal resistance for the whole.
A third term, thermal transmittance, incorporates the thermal conductance of a structure along with heat transfer due to convection and radiation. It is measured in the same units as thermal conductance and is sometimes known as the composite thermal conductance. The term U-value is another synonym.
In summary, for a plate of thermal conductivity k (the k value [3]), area A and thickness L:
* thermal conductance = k/L, measured in W·K−1·m−2;
* thermal resistance (R value) = L/k, measured in K·m²·W−1;
* thermal transmittance (U value) = 1/(Σ(L/k)) + convection + radiation, measured in W·K−1·m−2.
[edit] Textile industry
In textiles, a tog value may be quoted as a measure of thermal resistance in place of a measure in SI units.
[edit] Origins
The thermal conductivity of a system is determined by how atoms comprising the system interact. There are no simple, correct expressions for thermal conductivity. There are two different approaches for calculating the thermal conductivity of a system.
The first approach employs the Green-Kubo relations. Although this employs analytic expressions which in principle can be solved, in order to calculate the thermal conductivity of a dense fluid or solid using this relation requires the use of molecular dynamics computer simulation.
The second approach is based upon the relaxation time approach. Due to the anharmonicity within the crystal potential, the phonons in the system are known to scatter. There are three main mechanisms for scattering:
* Boundary scattering, a phonon hitting the boundary of a system;
* Mass defect scattering, a phonon hitting an impurity within the system and scattering;
* Phonon-phonon scattering, a phonon breaking into two lower energy phonons or a phonon colliding with another phonon and merging into one higher energy phonon.
Further information can be found in the publication "The Physics of Phonons" by G P Srivastava.
[edit] See also
* Heat conduction
* Heat transfer
* Heat transfer mechanisms
* Insulated pipes
* R-value
* Specific Heat
* Thermal bridge
* Thermal contact conductance
* Thermal diffusivity
* Thermal resistance in electronics
* Thermistor
* Thermocouple
* Electrical conductivity
[edit] External links
* Table with the Thermal Conductivity of the Elements
* http://physics.nist.gov/Pubs/SP811/appenB9.html
* http://www.npl.co.uk/thermal/faq_index.html#heat%20transfer%20property thermophysics FAQ5
* http://www.ornl.gov/roofs+walls/research/detailed_papers/rastra/dynamic.htm
* http://www.tak2000.com/data2.htm
* http://thermophys.savba.sk
* Calculation of the Thermal Conductivity of Glass Calculation of the Thermal Conductivity of Glass at Room Temperature from the Chemical Composition
* http://www.mathisinstruments.com/index.asp?pathinfo=/html/content/technology/tech_glossary.asp&dbbypass=
* Viscosity and Thermal Conductivity Equations for Nitrogen, Oxygen, Argon, and Air
[edit] References
1. ^ a b Thermal Conductivity of some common Materials
2. ^ Thermal Conductivity of Metals
3. ^ Definition of k value from Plastics New Zealand
* Callister, William (2003). "Appendix B", Materials Science and Engineering - An Introduction. John Wiley & Sons, INC, 757. ISBN 0-471-22471-5.
* Halliday, David; Resnick, Robert; & Walker, Jearl(1997). Fundamentals of Physics (5th ed.). John Wiley and Sons, INC., NY ISBN 0-471-10558-9.
* TM 5-852-6 AFR 88-19, Volume 6 (Army Corp of Engineers publication)
* Srivastava G. P (1990), "The Physics of Phonons." Adam Hilger, IOP Publishing Ltd, Bristol.
LEARN DESK
Thermal Conductivity - http://en.wikipedia.org/wiki/Thermal_conductivity
Heat Conductivity - http://en.wikipedia.org/wiki/Heat_conduction
Wednesday, August 27, 2008
Arctic Sea Ice Nears Record Low
By AP/DAN JOLING
Wednesday, Aug. 27, 2008
Time.com
[photo caption] A chunk of ice drifts after it separated from the Ward Hunt Ice Shelf off the north coast of Ellesmere Island in Canada.
Arctic Ocean sea ice has melted to the second lowest minimum since satellite observations began, according to scientists at the National Snow and Ice Data Center.
Sea ice melt recorded on Monday exceeded the low recorded in 2005, which had held second place.
With several weeks left in the melt season, ice in summer 2008 has a chance to diminish below the record low set last year, according to scientists at the National Snow and Ice Data Center.
Environmental groups said the ice melt was another alarm bell warning of global warming.
"It's an unfortunate sign that climate change is coming rapidly to the Arctic and that we really need to address the issue of global warming on a national level," said Christopher Krenz, Arctic project manager for Oceana.
"This is not surprising but it is alarming," said Deborah Williams, a former Interior Department special assistant for Alaska. "This was a relatively cool summer, and to have ice decrease to the second lowest minimum on record demonstrates that global warming's ongoing impact is profound."
The National Snow and Ice Data Center, based at the University of Colorado, reported the ice Monday melted below the 2005 minimum of 2.05 million square miles set on Sept. 21 that year. Exact figures will be released Wednesday.
Through the beginning of the melt season in May until early August, daily ice extent for 2008 closely tracked the values for 2005, the center said.
In early August 2005, the decline began to slow. In August 2008, however, the decline has remained steadily downward at a brisk pace.
The most recent ice retreat primarily reflects melt in the Chukchi Sea off Alaska's northwest coast and the East Siberian Seas off the coast of eastern Russia, according to the center.
The Chukchi Sea is home to one of two populations of Alaska polar bears.
Federal observers flying for a whale survey on Aug. 16 spotted nine polar bears swimming in open ocean in the Chukchi Sea. The bears were 15 to 65 miles off the Alaska shore. Some were swimming north, apparently trying to reach the polar ice edge, which on that day was 400 miles away.
Polar bears are powerful swimmers and have been recorded on swims of 100 miles but the ordeal can leave them exhausted and susceptible to drowning in high seas.
Sea ice is the primary habitat of polar bears. They depend on it to hunt their primary prey, ringed seals, which create lairs on ice for breeding maintain breathing holes with powerful claws.
Summer sea ice last year shrunk to about 1.65 million square miles, nearly 40 percent less than the long-term average between 1979 and 2000. Most climate modelers predict a continued downward spiral, possibly with an Arctic Ocean that's ice free during summer months by 2030 or sooner.
Krenz said the announcement Tuesday showed that last year's record low sea ice was not an anomaly. As ice covers fewer square miles of ocean, he said, warming will accelerate.
"It's going to accelerate climate change through changes in the reflectance of the Arctic," he said. "It's going from bright ice to a much darker ocean."
More square miles of dark ocean will absorb more heat. More warmth will accelerate melting of Arctic permafrost, allowing organic matter now frozen to melt and add to the greenhouse gas problem, he said.
"That allows for the breakdown of that by bacteria and other organisms that release CO2 or methane, depending on how the breakdown occurs," he said.
The effects faced by people in the Arctic eventually will reach the rest of the nation and the world, he warned.
Wednesday, Aug. 27, 2008
Time.com
[photo caption] A chunk of ice drifts after it separated from the Ward Hunt Ice Shelf off the north coast of Ellesmere Island in Canada.
Arctic Ocean sea ice has melted to the second lowest minimum since satellite observations began, according to scientists at the National Snow and Ice Data Center.
Sea ice melt recorded on Monday exceeded the low recorded in 2005, which had held second place.
With several weeks left in the melt season, ice in summer 2008 has a chance to diminish below the record low set last year, according to scientists at the National Snow and Ice Data Center.
Environmental groups said the ice melt was another alarm bell warning of global warming.
"It's an unfortunate sign that climate change is coming rapidly to the Arctic and that we really need to address the issue of global warming on a national level," said Christopher Krenz, Arctic project manager for Oceana.
"This is not surprising but it is alarming," said Deborah Williams, a former Interior Department special assistant for Alaska. "This was a relatively cool summer, and to have ice decrease to the second lowest minimum on record demonstrates that global warming's ongoing impact is profound."
The National Snow and Ice Data Center, based at the University of Colorado, reported the ice Monday melted below the 2005 minimum of 2.05 million square miles set on Sept. 21 that year. Exact figures will be released Wednesday.
Through the beginning of the melt season in May until early August, daily ice extent for 2008 closely tracked the values for 2005, the center said.
In early August 2005, the decline began to slow. In August 2008, however, the decline has remained steadily downward at a brisk pace.
The most recent ice retreat primarily reflects melt in the Chukchi Sea off Alaska's northwest coast and the East Siberian Seas off the coast of eastern Russia, according to the center.
The Chukchi Sea is home to one of two populations of Alaska polar bears.
Federal observers flying for a whale survey on Aug. 16 spotted nine polar bears swimming in open ocean in the Chukchi Sea. The bears were 15 to 65 miles off the Alaska shore. Some were swimming north, apparently trying to reach the polar ice edge, which on that day was 400 miles away.
Polar bears are powerful swimmers and have been recorded on swims of 100 miles but the ordeal can leave them exhausted and susceptible to drowning in high seas.
Sea ice is the primary habitat of polar bears. They depend on it to hunt their primary prey, ringed seals, which create lairs on ice for breeding maintain breathing holes with powerful claws.
Summer sea ice last year shrunk to about 1.65 million square miles, nearly 40 percent less than the long-term average between 1979 and 2000. Most climate modelers predict a continued downward spiral, possibly with an Arctic Ocean that's ice free during summer months by 2030 or sooner.
Krenz said the announcement Tuesday showed that last year's record low sea ice was not an anomaly. As ice covers fewer square miles of ocean, he said, warming will accelerate.
"It's going to accelerate climate change through changes in the reflectance of the Arctic," he said. "It's going from bright ice to a much darker ocean."
More square miles of dark ocean will absorb more heat. More warmth will accelerate melting of Arctic permafrost, allowing organic matter now frozen to melt and add to the greenhouse gas problem, he said.
"That allows for the breakdown of that by bacteria and other organisms that release CO2 or methane, depending on how the breakdown occurs," he said.
The effects faced by people in the Arctic eventually will reach the rest of the nation and the world, he warned.
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