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..."
----------------------------------------------------------
SCIENCE DAILY
http://www.sciencedaily.com/releases/2006/05/060522151248.htm
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
Foundation.
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