[Editors] MIT: Climate change odds much worse than thought

[Elizabeth Thomson]

For Immediate Release
TUESDAY, MAY. 19, 2009

Contact: Elizabeth A. Thomson, MIT News Office
E: thomson at mit.edu, T: 617-258-5402

======================================
MIT: Climate change odds much worse than thought
--New analysis shows warming could be double previous estimates
======================================

Photo and Graphic Available

CAMBRIDGE, Mass.--The most comprehensive modeling yet carried out on  
the likelihood of how much hotter the Earth’s climate will get in this  
century shows that without rapid and massive action, the problem will  
be about twice as severe as previously estimated six years ago — and  
could be even worse than that.

The study uses the MIT Integrated Global Systems Model, a detailed  
computer simulation of global economic activity and climate processes  
that has been developed and refined by the Joint Program on the  
Science and Policy of Global Change since the early 1990s. The new  
research involved 400 runs of the model with each run using slight  
variations in input parameters, selected so that each run has about an  
equal probability of being correct based on present observations and  
knowledge. Other research groups have estimated the probabilities of  
various outcomes, based on variations in the physical response of the  
climate system itself. But the MIT model is the only one that  
interactively includes detailed treatment of possible changes in human  
activities as well — such as the degree of economic growth, with its  
associated energy use, in different countries.

Study co-author Ronald Prinn, the co-director of the Joint Program and  
director of MIT’s Center for Global Change Science, says that,  
regarding global warming, it is important “to base our opinions and  
policies on the peer-reviewed science,” he says. And in the peer- 
reviewed literature, the MIT model, unlike any other, looks in great  
detail at the effects of economic activity coupled with the effects of  
atmospheric, oceanic and biological systems. “In that sense, our work  
is unique,” he says.

The new projections, published this month in the American  
Meteorological Society’s Journal of Climate, indicate a median  
probability of surface warming of 5.2 degrees Celsius by 2100, with a  
90% probability range of 3.5 to 7.4 degrees. This can be compared to a  
median projected increase in the 2003 study of just 2.4 degrees. The  
difference is caused by several factors rather than any single big  
change. Among these are improved economic modeling and newer economic  
data showing less chance of low emissions than had been projected in  
the earlier scenarios. Other changes include accounting for the past  
masking of underlying warming by the cooling induced by 20th century  
volcanoes, and for emissions of soot, which can add to the warming  
effect. In addition, measurements of deep ocean temperature rises,  
which enable estimates of how fast heat and carbon dioxide are removed  
from the atmosphere and transferred to the ocean depths, imply lower  
transfer rates than previously estimated.

Prinn says these and a variety of other changes based on new  
measurements and new analyses changed the odds on what could be  
expected in this century in the “no policy” scenarios — that is, where  
there are no policies in place that specifically induce reductions in  
greenhouse gas emissions. Overall, the changes “unfortunately largely  
summed up all in the same direction,” he says. “Overall, they stacked  
up so they caused more projected global warming.”

While the outcomes in the “no policy” projections now look much worse  
than before, there is less change from previous work in the projected  
outcomes if strong policies are put in place now to drastically curb  
greenhouse gas emissions. Without action, “there is significantly more  
risk than we previously estimated,” Prinn says. “This increases the  
urgency for significant policy action.”

To illustrate the range of probabilities revealed by the 400  
simulations, Prinn and the team produced a “roulette wheel” that  
reflects the latest relative odds of various levels of temperature  
rise. The wheel provides a very graphic representation of just how  
serious the potential climate impacts are.

“There’s no way the world can or should take these risks,” Prinn says.  
And the odds indicated by this modeling may actually understate the  
problem, because the model does not fully incorporate other positive  
feedbacks that can occur, for example, if increased temperatures  
caused a large-scale melting of permafrost in arctic regions and  
subsequent release of large quantities of methane, a very potent  
greenhouse gas. Including that feedback “is just going to make it  
worse,” Prinn says.

The lead author of the paper describing the new projections is Andrei  
Sokolov, research scientist in the Joint Program. Other authors,  
besides Sokolov and Prinn, include Peter H. Stone, Chris E. Forest,  
Sergey Paltsev, Adam Schlosser, Stephanie Dutkiewicz, John Reilly,  
Marcus Sarofim, Chien Wang and Henry D. Jacoby, all of the MIT Joint  
Program on the Science and Policy of Global Change, as well as Mort  
Webster of MIT’s Engineering Systems Division and D. Kicklighter, B.  
Felzer and J. Melillo of the Marine Biological Laboratory at Woods Hole.

Prinn stresses that the computer models are built to match the known  
conditions, processes and past history of the relevant human and  
natural systems, and the researchers are therefore dependent on the  
accuracy of this current knowledge. Beyond this, “we do the research,  
and let the results fall where they may,” he says. Since there are so  
many uncertainties, especially with regard to what human beings will  
choose to do and how large the climate response will be, “we don’t  
pretend we can do it accurately. Instead, we do these 400 runs and  
look at the spread of the odds.”

Because vehicles last for years, and buildings and powerplants last  
for decades, it is essential to start making major changes through  
adoption of significant national and international policies as soon as  
possible, Prinn says. “The least-cost option to lower the risk is to  
start now and steadily transform the global energy system over the  
coming decades to low or zero greenhouse gas-emitting technologies.”

This work was supported in part by grants from the Office of Science  
of the U.S. Dept. of Energy, and by the industrial and foundation  
sponsors of the MIT Joint Program on the Science and Policy of Global  
Change.

--END--

Written by David Chandler, MIT News Office
-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://mailman.mit.edu/pipermail/editors/attachments/20090519/af65cdd6/attachment.htm