Adding Fossil Fuel to the Fire: Researchers Find Higher Global Warming Estimates More Likely

Posted: June 5, 2006 at 1:00 am, Last Updated: November 30, -0001 at 12:00 am

Warm Earth
This NASA image shows where more or less heat, in the form of longwave radiation, is emanating from the top of Earth’s atmosphere.
Image courtesy Barbara Summey, NASA Goddard Visualization Analysis Lab, based upon data processed by Takmeng Wong, CERES Science Team, NASA Langley Research Center

By Tara Laskowski

With the global warming debate heating up in the news lately, researchers at George Mason University and the independent Center for Ocean-Land-Atmosphere Studies (COLA) recently conducted a comprehensive, and somewhat controversial, study that showed global warming estimates for the next century might be higher than we think.

The study put current climate models to the test and for the first time ranked these complex modeling systems in terms of accuracy. Results show that when models currently working to predict the Earth’s climate are ranked in this way, the more reliable models tend to project higher estimates of global warming for the next century.

The paper “Climate Model Fidelity and Projections of Climate Change,” which appeared this month in Geophysical Research Letters, presents a detailed mathematical analysis of the model simulations prepared for the Intergovernmental Panel on Climate Change (IPPC). It predicts higher estimates of global warming – 4 to 5º C as opposed to the model consensus range of 2 to 4º C – may be more likely.

This is the first study to relate the ranking of climate model accuracy to their simulations of future climate. In previous studies, the scientific community has been reluctant to evaluate models in relation to one another, but George Mason and COLA scientists have used this comparison to stress an important trend in the current predictions of global warming.

Some Climate Models Better Than Others

“Most reports of IPCC projections treat all models as equally good, but we have found that some models do a

Jagadish Shukla
Jagadish Shukla, lead author on a new study that compares global warming simulations.
Creative Services photo

better job of simulating the past century than others,” says Jagadish Shukla, professor in the School of Computational Sciences and the paper’s lead author.

“Giving the higher fidelity models more weight implies a higher future global warming estimate than expected heretofore.”

The researchers – Shukla, Timothy DelSole, Michael Fennessy, Jim Kinter and Daniel Paolino – looked at the results of 14 current climate models from 10 different premier laboratories in five different countries.

The identities of the models in the study were omitted from the paper and are being withheld to avoid promoting or criticizing individual models or modeling groups.

“It is somewhat controversial in the climate modeling community to rank the models, primarily because the climate system is complex, and an individual model may do well on one aspect of climate and poorly on other aspects,” says Kinter, director of COLA, a research center in Calverton, Md., and an associate professor of climate dynamics at George Mason.

“It is also controversial from a political point of view, because the models are associated with particular institutions and their countries of origin, and no institution or country wants its model to be found to be inferior to other models.

“As a result, the usual IPCC practice of model analysis is to consider all models as equals. Our result – that the more accurate the model, the higher the estimate of future global warming – suggests that equal weighting among all models may lead to an underestimate.”

Weighing in on the Earth’s Future

Changes predicted in the Earth’s climate for the next 100 years have scientists concerned. With the release of the Al Gore documentary, “An Inconvenient Truth,” as well as numerous headline-making studies on global warming, this concern has reached a wider audience.

Mason and COLA researchers hope their results will throw more light on the subject.

“This paper addresses one of the most important issues that faces both the scientific community and the international policy community, namely, the magnitude of global warming, because there is so much at stake for the future of humankind and the planetary ecosystem,” says Shukla.

If the Earth warms 4 or 5 degrees on average in the next century, that change could have a significant impact on certain geographic areas. For example, while regional impacts are more uncertain than the global average, says Kinter, the metropolitan Washington, D.C., area might be affected in the following ways:

  • Summer temperatures would probably reach or exceed 100º F more often.
  • The area would probably get much less winter snow; possibly none.
  • There would probably be an increase in pests such as mosquitoes that normally die out during colder temperatures.

“The sort of changes we are talking about are relatively small, but because the changes we have already seen in the past 100 years are unprecedented with respect to the past 400,000 years of the planet’s history, there is concern,” says Kinter.

“Our results suggest that the consensus of all climate models may be an underestimate of how much change could be in store.”

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