 |
|
World to be even hotter by century's end
May 25, 2006BERKELEY - If Earth's past cycles of warming and cooling are any indication, temperatures by the end of the century will be even hotter than current climate models predict, according to a report by University of California, Berkeley, researchers.
The scientists based their conclusion on a study of Antarctic ice cores containing a 360,000-year record of global temperature and levels of carbon dioxide and methane-two of the major greenhouse gases implicated in global warming. They found that during periods of warming, greenhouse gas levels rose and created significantly higher temperatures than would be expected solely from the increased intensity of sunlight that triggered these warm periods.
Though the ice core data do not point to specific processes that amplify the warming, the researchers suspect that it is due to warmer soils and oceans giving off more CO2 and methane, which add to the greenhouse effect of CO2 from fossil fuel burning and other human activities.
Thus, while current models predict temperature increases of 1.5 to 4.5 degrees Celsius (2.7 to 8.1 degrees Fahrenheit) from a doubling of atmospheric carbon dioxide levels, the natural processes injecting more CO2 into the atmosphere will lead to temperature increases of 1.6 to 6 degrees Celsius (2.9 to 10.8 degrees Fahrenheit), with the higher temperatures more likely, the researchers said.
"We are underestimating the magnitude of warming because we are ignoring the extra carbon dioxide dumped into the atmosphere because of warming," said John Harte, UC Berkeley professor of energy and resources and of environmental science, policy & management. "Warming gets an extra kick from CO2 feedback."
"The warming caused by our release of CO2 triggers changes in the Earth system that lead to release of more CO2 to the atmosphere," added co-author Margaret Torn, a UC Berkeley adjunct associate professor of energy and resources and staff scientist at Lawrence Berkeley National Laboratory. "If that is the case, then every bit of CO2 release now is actually committing us to a larger CO2 change in the atmosphere."
The result, Harte and Torn conclude in their paper, is "that the upper value of warming that is projected for the end of the 21st century, 5.8ºC [10.4ºF], could be increased to 7.7ºC [13.9ºF], or nearly 2ºC additional warming."
The report is scheduled for publication in the May 26 issue of Geophysical Research Letters. That issue also will contain an article that looks at the same effect over a shorter time scale, confirming the amplification reported by Harte and Torn and suggesting that it may be even greater.
Current climate models, called General Circulation Models, start from fundamental physical processes to calculate a probable temperature increase based on likely atmospheric carbon dioxide levels, typically a doubling of today's CO2 concentration. These models also include feedback mechanisms that boost or moderate warming, such as the increased heat absorption expected when highly reflective ice sheets and glaciers melt; or the effect of more atmospheric water vapor on the formation of clouds, which both reflect sunlight and insulate the Earth.
But models are only now beginning to take into account the extra carbon dioxide and methane injected into the atmosphere as global temperatures increase. Though this is expected because warmer soils decompose faster, releasing more CO2, and because warmer oceans outgas more CO2, scientists have yet to quantify the full impact of these processes.
"Without a mechanism, people feel uncomfortable putting these processes in a model. I think that's a big mistake," Harte said.
Luckily, it's possible to estimate the effect of CO2 feedback by looking at how the Earth responded to past cycles of warming and cooling, which were caused by natural variations in the strength of sunlight hitting Earth, rather than by human production of greenhouse gases. Ice cores drilled in the Vostok ice sheet in 1998 and 1999 by Russia, France and the United States span nearly 420,000 years and carry information about four major climate cycles and many smaller temperature swings. In 1999, scientists measured CO2 and methane levels from gas trapped in bubbles in the ice, and have estimated global temperature based on oxygen isotope and deuterium ratios. UC Berkeley's Kurt Cuffey, professor of geography and earth and planetary science, updated these measurements in 2001.
Climate scientists immediately saw that the ice core data imply a strong positive feedback to global CO2 and methane levels, but how much this impacted warming trends was unclear.
Harte, a physicist by training, and Torn devised a way to use these data and current global climate models to estimate the effect of increased CO2 entering the atmosphere as a result of warming, called the "gain," analogous to the gain of an electronic amplifier-the factor by which output power increases. From Cuffey's data, Harte and Torn were able to extract the effect of temperature on CO2 and methane levels. They calculated the reverse-the effect of CO2 and methane levels on temperature, or the so-called climate sensitivity-from climate models, using a number consistent with a new estimate published in the April 20 issue of Nature.
Harte and Torn added the resultant gains from CO2 and methane to the gain already known for other climate feedbacks, in particular the largest source, increased atmospheric water vapor, to get a total gain that they used to calculate the temperature increase that would result from a doubling of current CO2 levels.
Both researchers emphasize that the large temperature range they predict-1.6 to 6 degrees Celsius-does not mean that we have an equal chance of ending up with less warming as with greater warming. In other words, it doesn't mean that the uncertainties are symmetric about an average increase of 3.8ºC.
"People see this uncertainty and think that we have an equal probability of dodging a bullet as catching it. That is a fallacy," Torn said.
"By giving the appearance of symmetric feedback, people have an excuse to say, 'Maybe we don't have to worry so much,'" Harte said. "But while there are uncertainties in the feedbacks, all the major feedbacks are positive, meaning they would increase warming, and we know of no significant negative feedbacks that would slow warming."
While Harte acknowledges that the future may not look like past periods of global warming, "in the absence of contradictory evidence, we have to assume the future will respond like the past."
"Whatever the mechanisms that cause temperature to create a change in CO2 and methane, they are repeatable again and again and again over many cooling and warming cycles. So, although the world is different today than it was then, we don't have a basis for ignoring them," Torn added.
Harte has been conducting studies on experimental plots in the Rocky Mountains that would quantify the effect of warmer temperatures on soil carbon. He and his colleagues found that artificially heated plots lost significant soil carbon to the atmosphere as CO2, compared to control plots. Thus, he said, the effect of heating on the carbon cycle in his plots is to generate a positive feedback, though he noted that this might be a short-term effect. The long term effect, however, is unknown, as is the effect of warming in other habitats.
"We need to know the effect of warmer temperatures in all different habitats, not just temperate Rocky Mountain forests but also the tropics and European boreal forests and Eastern U.S. deciduous forests and savanna and prairie. There are huge data gaps," he said.
Torn noted, however, that humans are the biggest unknown.
"To predict the future, you have to guess how much CO2 levels will go up. That depends on the biggest uncertainty of all-what humans decide to do. Do we get smart and prevent CO2 emissions? Do we continue with business as usual? Or will we end up somewhere in between?"
The work was supported by the U.S. Department of Energy's Climate Change Research Division and by the National Science Foundation.
University of California, Berkeley
Thus, while current models predict temperature increases of 1.5 to 4.5 degrees Celsius (2.7 to 8.1 degrees Fahrenheit) from a doubling of atmospheric carbon dioxide levels, the natural processes injecting more CO2 into the atmosphere will lead to temperature increases of 1.6 to 6 degrees Celsius (2.9 to 10.8 degrees Fahrenheit), with the higher temperatures more likely, the researchers said.
"We are underestimating the magnitude of warming because we are ignoring the extra carbon dioxide dumped into the atmosphere because of warming," said John Harte, UC Berkeley professor of energy and resources and of environmental science, policy & management. "Warming gets an extra kick from CO2 feedback."
"The warming caused by our release of CO2 triggers changes in the Earth system that lead to release of more CO2 to the atmosphere," added co-author Margaret Torn, a UC Berkeley adjunct associate professor of energy and resources and staff scientist at Lawrence Berkeley National Laboratory. "If that is the case, then every bit of CO2 release now is actually committing us to a larger CO2 change in the atmosphere."
The result, Harte and Torn conclude in their paper, is "that the upper value of warming that is projected for the end of the 21st century, 5.8ºC [10.4ºF], could be increased to 7.7ºC [13.9ºF], or nearly 2ºC additional warming."
The report is scheduled for publication in the May 26 issue of Geophysical Research Letters. That issue also will contain an article that looks at the same effect over a shorter time scale, confirming the amplification reported by Harte and Torn and suggesting that it may be even greater.
Current climate models, called General Circulation Models, start from fundamental physical processes to calculate a probable temperature increase based on likely atmospheric carbon dioxide levels, typically a doubling of today's CO2 concentration. These models also include feedback mechanisms that boost or moderate warming, such as the increased heat absorption expected when highly reflective ice sheets and glaciers melt; or the effect of more atmospheric water vapor on the formation of clouds, which both reflect sunlight and insulate the Earth.
But models are only now beginning to take into account the extra carbon dioxide and methane injected into the atmosphere as global temperatures increase. Though this is expected because warmer soils decompose faster, releasing more CO2, and because warmer oceans outgas more CO2, scientists have yet to quantify the full impact of these processes.
"Without a mechanism, people feel uncomfortable putting these processes in a model. I think that's a big mistake," Harte said.
Luckily, it's possible to estimate the effect of CO2 feedback by looking at how the Earth responded to past cycles of warming and cooling, which were caused by natural variations in the strength of sunlight hitting Earth, rather than by human production of greenhouse gases. Ice cores drilled in the Vostok ice sheet in 1998 and 1999 by Russia, France and the United States span nearly 420,000 years and carry information about four major climate cycles and many smaller temperature swings. In 1999, scientists measured CO2 and methane levels from gas trapped in bubbles in the ice, and have estimated global temperature based on oxygen isotope and deuterium ratios. UC Berkeley's Kurt Cuffey, professor of geography and earth and planetary science, updated these measurements in 2001.
Climate scientists immediately saw that the ice core data imply a strong positive feedback to global CO2 and methane levels, but how much this impacted warming trends was unclear.
Harte, a physicist by training, and Torn devised a way to use these data and current global climate models to estimate the effect of increased CO2 entering the atmosphere as a result of warming, called the "gain," analogous to the gain of an electronic amplifier-the factor by which output power increases. From Cuffey's data, Harte and Torn were able to extract the effect of temperature on CO2 and methane levels. They calculated the reverse-the effect of CO2 and methane levels on temperature, or the so-called climate sensitivity-from climate models, using a number consistent with a new estimate published in the April 20 issue of Nature.
Harte and Torn added the resultant gains from CO2 and methane to the gain already known for other climate feedbacks, in particular the largest source, increased atmospheric water vapor, to get a total gain that they used to calculate the temperature increase that would result from a doubling of current CO2 levels.
Both researchers emphasize that the large temperature range they predict-1.6 to 6 degrees Celsius-does not mean that we have an equal chance of ending up with less warming as with greater warming. In other words, it doesn't mean that the uncertainties are symmetric about an average increase of 3.8ºC.
"People see this uncertainty and think that we have an equal probability of dodging a bullet as catching it. That is a fallacy," Torn said.
"By giving the appearance of symmetric feedback, people have an excuse to say, 'Maybe we don't have to worry so much,'" Harte said. "But while there are uncertainties in the feedbacks, all the major feedbacks are positive, meaning they would increase warming, and we know of no significant negative feedbacks that would slow warming."
While Harte acknowledges that the future may not look like past periods of global warming, "in the absence of contradictory evidence, we have to assume the future will respond like the past."
"Whatever the mechanisms that cause temperature to create a change in CO2 and methane, they are repeatable again and again and again over many cooling and warming cycles. So, although the world is different today than it was then, we don't have a basis for ignoring them," Torn added.
Harte has been conducting studies on experimental plots in the Rocky Mountains that would quantify the effect of warmer temperatures on soil carbon. He and his colleagues found that artificially heated plots lost significant soil carbon to the atmosphere as CO2, compared to control plots. Thus, he said, the effect of heating on the carbon cycle in his plots is to generate a positive feedback, though he noted that this might be a short-term effect. The long term effect, however, is unknown, as is the effect of warming in other habitats.
"We need to know the effect of warmer temperatures in all different habitats, not just temperate Rocky Mountain forests but also the tropics and European boreal forests and Eastern U.S. deciduous forests and savanna and prairie. There are huge data gaps," he said.
Torn noted, however, that humans are the biggest unknown.
"To predict the future, you have to guess how much CO2 levels will go up. That depends on the biggest uncertainty of all-what humans decide to do. Do we get smart and prevent CO2 emissions? Do we continue with business as usual? Or will we end up somewhere in between?"
The work was supported by the U.S. Department of Energy's Climate Change Research Division and by the National Science Foundation.
University of California, Berkeley
Climate Models Current Events and Climate Models News RSSFuture Risk of Hurricanes: The Role of Climate Change
Researchers are homing in on the hurricane-prone Gulf of Mexico and Caribbean Sea to assess the likely changes, between now and the middle of the century, in the frequency, intensity, and tracks of these powerful storms. Initial results are expected early next year.
Waterborne disease risk upped in Great Lakes
An anticipated increased incidence of climate-related extreme rainfall events in the Great Lakes region may raise the public health risk for the 40 million people who depend on the lakes for their drinking water, according to a new study.
Brookhaven Scientists Take Off for Southeastern Pacific Climate Study
During October and November 2008, some 150 scientists from 40 institutions in eight nations - including scientists from the U.S. Department of Energy's (DOE) Brookhaven National Laboratory - will take part in an international field experiment designed to make observations of critical components of the climate system of the southeastern Pacific.
Green coffee-growing practices buffer climate-change impacts
Chalk up another environmental benefit for shade-grown Latin American coffee: University of Michigan researchers say the technique will provide a buffer against the ravages of climate change in the coming decades.
Looking for water on Mars
NASA's Phoenix Scout Lander reached Mars on May 25,, opened a soils lab, and started looking for water. Phoenix uses a robotic scoop arm to deliver regolith samples to the suite of instruments aboard the Lander--with one exception.
IMPACTS: On the Threshold of Abrupt Climate Changes
Abrupt climate change is a potential menace that hasn't received much attention. That's about to change. Through its Climate Change Prediction Program, the U.S. Department of Energy's Office of Biological and Environmental Research (OBER) recently launched IMPACTS - Investigation of the Magnitudes and Probabilities of Abrupt Climate Transitions - a program led by William Collins of Berkeley Lab's Earth Sciences Division (ESD) that brings together six national laboratories to attack the problem of abrupt climate change, or ACC.
Climate Computer Modeling Heats Up
New "petascale" computer models depicting detailed climate dynamics, and building the foundation for the next generation of complex climate models, are in the offing.
Valley networks on Mars formed during long period of episodic flooding
A new study suggests that ancient features on the surface of Mars called valley networks were carved by recurrent floods during a long period when the martian climate may have been much like that of some arid or semiarid regions on Earth.
Science paper examines role of aerosols in climate change
A group of scientists affiliated with the International Geosphere-Biosphere Programme (IGBP) have proposed a new framework to account more accurately for the effects of aerosols on precipitation in climate models.
New clues to air circulation in the atmosphere
Air circulates above the Earth in four distinct cells, with two either side of the equator, says new research out today (21 August) in Science.
More Climate Models Current Events and Climate Models News Articles
 | Economic Models of Climate Change: A Critique by Stephen J. De Canio The climate policy debate has been dominated by economic estimates of the costs of policies to reduce greenhouse gas emissions. Yet the models used to derive those estimates are based on assumptions that have largely gone untested. The conventional approach embodies structural features that rule out alternative market outcomes. In addition, the distribution of "climate rights" is crucial to... |
 | Climate Confusion: How Global Warming Hysteria Leads to Bad Science, Pandering Politicians and Misguided Policies that Hurt the Poor by Roy Spencer If you listen to the media, you would think that man-made environmental catastrophe was about to engulf the world and imperil civilization. From Al Gore's An Inconvenient Truth to nightly jeremiads about CO2 emissions and carbon footprints, we are bombarded around the clock with alarmist reports that disasterous global warming is on the rise and that it's our fault. In Climate Confusion, noted... |
 | Fundamentals of Ocean Climate Models by Stephen Griffies This book sets forth the physical, mathematical, and numerical foundations of computer models used to understand and predict the global ocean climate system. Aimed at students and researchers of ocean and climate science who seek to understand the physical content of ocean model equations and numerical methods for their solution, it is largely general in formulation and employs modern... |
 | Stochastic Climate Models (Progress in Probability) This book presents a collection of articles written by mathematicians and physicists, designed to describe the state of the art in climate models with stochastic input. They are based on a selection of lectures given at the interdisciplinary Workshop on Stochastic Climate Models held in Chorin, Germany, from May 31 to June 2, 1999. The emphasis is on reduced models tractable with advanced tools... |
 | Atmospheric Chemistry: Models and Predictions for Climate and Air Quality by Christine S. Sloane, T. W. Tesche This book draws upon the knowledge and experience of modeling experts currently engaged in conducting assessments regarding the predictive strength of atmospheric models. The book covers all of the major important atmospheric areas, including large scale models for ozone depletion and global warming, regional scale models for urban smog (ozone and visibility impairment) and acid rain, as well as... |
 | Antarctic climate at the Eocene/Oligocene boundary - climate model sensitivity to high latitude vegetation type and comparisons with the palaeobotanical ... Palaeoclimatology, Palaeoecology] by V.C. Thorn, R. DeConto This digital document is a journal article from Palaeogeography, Palaeoclimatology, Palaeoecology, published by Elsevier in . The article is delivered in HTML format and is available in your Amazon.com Media Library immediately after purchase. You can view it with any web browser.Description: Simulated climate for the Antarctic continent using the GENESIS (Version 2.1) Global Climate Model with... |
 | Pre-industrial-potential and Last Glacial Maximum global vegetation simulated with a coupled climate-biosphere model: diagnosis of bioclimatic relationships ... article from: Global and Planetary Change] by M. Crucifix, R.A. Betts, C.D. Hewitt This digital document is a journal article from Global and Planetary Change, published by Elsevier in 2005. The article is delivered in HTML format and is available in your Amazon.com Media Library immediately after purchase. You can view it with any web browser.Description: The global climate-vegetation model HadSM3_TRIFFID has been used to estimate the equilibrium states of climate and... |
| Future climate extreme events in the Mediterranean simulated by a regional climate model: a first approach [An article from: Global and Planetary Change] by E. Sanchez, C. Gallardo, M.A. Gaertner, A Arribas This digital document is a journal article from Global and Planetary Change, published by Elsevier in 2004. The article is delivered in HTML format and is available in your Amazon.com Media Library immediately after purchase. You can view it with any web browser.Description: Within the frame of PRUDENCE (Prediction of Regional scenarios and Uncertainties for Defining EuropeaN Climate change risks... |
 | Game theoretic models for climate change negotiations [An article from: European Journal of Operational Research] by F. Forgo, J. Fulop, M. Prill This digital document is a journal article from European Journal of Operational Research, published by Elsevier in 2005. The article is delivered in HTML format and is available in your Amazon.com Media Library immediately after purchase. You can view it with any web browser.Description: Negotiations to reduce greenhouse gas accumulation in the atmosphere are modeled as extensive games of perfect... |
 | Land Surface-Atmosphere Interactions for Climate Modeling: Observations, Models and Analysis (Reprinted from Surveys in Geophysics, Vol 12, Nos 1-3) |
| © 2008 BrightSurf.com |