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hotter than expected

" Their results point to global temperatures at the end of this 
century that may be significantly higher than current climate models 
are predicting."

"Torn is an authority on carbon and nutrient cycling in terrestrial 
ecosystems, and on the impacts of anthropogenic activities on 
terrestrial ecosystem processes. Harte has been a leading figure for 
the past two decades on climate-ecosystem interactions..."


Source: Lawrence Berkeley National Laboratory
Posted: May 22, 2006

Feedback Loops In Global Climate Change Point To A Very Hot 21st Century

Studies have shown that global climate change can set-off positive 
feedback loops in nature which amplify warming and cooling trends. 
Now, researchers with the Lawrence Berkeley National Laboratory 
(Berkeley Lab) and the University of California at Berkeley have been 
able to quantify the feedback implied by past increases in natural 
carbon dioxide and methane gas levels. Their results point to global 
temperatures at the end of this century that may be significantly 
higher than current climate models are predicting.

Using as a source the Vostok ice core, which provides information 
about glacial-interglacial cycles over hundreds of thousands of 
years, the researchers were able to estimate the amounts of carbon 
dioxide and methane, two of the principal greenhouse gases, that were 
released into the atmosphere in response to past global warming 
trends. Combining their estimates with standard climate model 
assumptions, they calculated how much these rising concentration 
levels caused global temperatures to climb, further increasing carbon 
dioxide and methane emissions, and so on.

"The results indicate a future that is going to be hotter than we 
think," said Margaret Torn, who heads the Climate Change and Carbon 
Management program for Berkeley Lab's Earth Sciences Division, and is 
an Associate Adjunct Professor in UC Berkeley's Energy and Resources 
Group. She and John Harte, a UC Berkeley professor in the Energy and 
Resources Group and in the Ecosystem Sciences Division of the College 
of Natural Resources, have co-authored a paper entitled: Missing 
feedbacks, asymmetric uncertainties, and the underestimation of 
future warming, which appears in the May, 2006 issue of the journal 
Geophysical Research Letters (GRL).

In their GRL paper, Torn and Harte make the case that the current 
climate change models, which are predicting a global temperature 
increase of as much as 5.8 degrees Celsius by the end of the century, 
may be off by nearly 2.0 degrees Celsius because they only take into 
consideration the increased greenhouse gas concentrations that result 
from anthropogenic (human) activities.

"If the past is any guide, then when our anthropogenic greenhouse gas 
emissions cause global warming, it will alter earth system processes, 
resulting in additional atmospheric greenhouse gas loading and 
additional warming," said Torn.

Torn is an authority on carbon and nutrient cycling in terrestrial 
ecosystems, and on the impacts of anthropogenic activities on 
terrestrial ecosystem processes. Harte has been a leading figure for 
the past two decades on climate-ecosystem interactions, and has 
authored or co-authored numerous books on environmental sciences, 
including the highly praised Consider a Spherical Cow: A Course in 
Environmental Problem Solving.

In their GRL paper, Torn and Harte provide an answer to those who 
have argued that uncertainties in climate change models make it 
equally possible that future temperature increases could as be 
smaller or larger than what is feared. This argument has been based 
on assumptions about the uncertainties in climate prediction.

However, in their GRL paper, Torn and Harte conclude that: "A 
rigorous investigation of the uncertainties in climate change 
prediction reveals that there is a higher risk that we will 
experience more severe, not less severe, climate change than is 
currently forecast."

Serious scientific debate about global warming has ended, but the 
process of refining and improving climate models - called general 
circulation models or GCMs - is ongoing. Current GCMs project 
temperature increases at the end of this century based on greenhouse 
gas emissions scenarios due to anthropogenic activities. Carbon 
dioxide in the atmosphere, for example, has already climbed from a 
pre-industrial 280 parts per million (ppm) to 380 ppm today, causing 
a rise in global temperature of 0.6 degrees Celsius. The expectations 
are for atmospheric carbon dioxide to soar beyond 550 ppm by 2100 
unless major changes in energy supply and demand are implemented.

Concerning as these projection are, they do not take into account 
additional amounts of carbon dioxide and methane released when rising 
temperatures trigger ecological and chemical responses, such as 
warmer oceans giving off more carbon dioxide, or warmer soils 
decomposing faster, liberating ever increasing amounts of carbon 
dioxide and methane. The problem has been an inability to quantify 
the impact of Nature's responses in the face of overwhelming 
anthropogenic input. Torn and Harte were able to provide this 
critical information by examining the paleo data stored in ancient 
ice cores.

"Paleo data can provide us with an estimate of the greenhouse gas 
increases that are a natural consequence of global warming," said 
Torn. "In the absence of human activity, these greenhouse gas 
increases are the dominant feedback mechanism."

In examining data recorded in the Vostok ice core, scientists have 
known that cyclic variations in the amount of sunlight reaching the 
earth trigger glacial-interglacial cycles. However, the magnitude of 
warming and cooling temperatures cannot be explained by variations in 
sunlight alone. Instead, large rises in temperatures are more the 
result of strong upsurges in atmospheric carbon dioxide and methane 
concentrations set-off by the initial warming.

Using deuterium-corrected temperature records for the ice cores, 
which yield hemispheric rather than local temperature conditions, GCM 
climate sensitivity, and a mathematical formula for quantifying 
feedback effects, Torn and Harte calculated the magnitude of the 
greenhouse gas-temperature feedback on temperature.

"Our results reinforce the fact that every bit of greenhouse gas we 
put into the atmosphere now is committing us to higher global 
temperatures in the future and we are already near the highest 
temperatures of the past 700,000 years," Torn said. "At this point, 
mitigation of greenhouse gas emissions is absolutely critical."

The feedback loop from greenhouse gas concentrations also has a 
reverse effect, the authors state, in that reduced atmospheric levels 
can enhance the cooling of global temperatures. This presents at 
least the possibility of extra rewards if greenhouse gas levels in 
the atmosphere could be rolled back, but the challenge is great as 
Harte explained.

"If we reduce emissions so much that the atmospheric concentration of 
carbon dioxide actually starts to come down and the global 
temperature also starts to decrease, then the feedback would work for 
us and speed the recovery," Harte said. "However, if we reduce 
emissions by an amount that greatly reduces the rate at which the 
carbon dioxide level in the atmosphere increases, but don't cut 
emissions back to the point where the carbon dioxide level actually 
decreases, then the positive feedback still works against us."

This research was supported by the U.S. Department of Energy's 
Climate Change Research Division and by the National Science 


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