Climate Modeling is Far From a Precise Science

Climate Modeling is Far From a Precise Science

A recent study of paleoclimate, the results of which appear in the August issue of Nature Geoscience, finds that today’s climate models do not accurately predict the most similar previous episode of climate warming in the geologic record.

California Republic, August 21, 2009

A recent study of paleoclimate, the results of which appear in the August issue of Nature Geoscience, finds that today’s climate models do not accurately predict the most similar previous episode of climate warming in the geologic record. While this should not cast doubt on the value of climate models in tools to analyze drivers and projections of climate change, the study does point out that our understanding of climate dynamics remains imperfect

The authors of the study, Carbon dioxide forcing alone insufficient to explain Palaeocene–Eocene Thermal Maximum warming, include Richard E. Zeebe of the School of Ocean and Earth Science and Technology, Department of Oceanography, University of Hawaii at Manoa; James C. Zachos of the Earth and Planetary Sciences Department, University of California, Santa Cruz; and Gerald R. Dickens of the Department of Earth Sciences, Rice University. Their research focused on the models used by the Intergovernmental Panel on Climate Change (IPCC) to generate climate projections.

In an analysis of proxy climate data from the geologic ocean sediment records, the researchers studied the ability of these models to replicate the warming observed during the Palaeocene–Eocene Thermal Maximum (PETM), a period of 5-9 degree C warming that occurred about 55 million years ago. The researchers found that the models predicted only about half of the observed warming, indicating that an additional mechanism, beyond carbon dioxide concentrations, was responsible for a significant amount of the warming during that period.

The PETM was not, of course, exactly the same sort of conditions we have today. Conditions at the beginning of the warming trend were different, with initial CO2 concentrations strikingly higher, for reasons that are not known. For the most part, there were no large amounts of ice on the earth’s surface during the PETM, and the energy dynamics of ice are significant. Nonetheless, the inability of the climate models adequately to capture a previous episode of climate change does suggest that our models are missing potentially key relationships.

This is not the first time research has indicated that today’s climate models fail to capture important climate dynamics. Other research has suggested that some cloud dynamics, solar activity, and other factors, are not well understood or integrated into climate models.

This new research published in Nature Geoscience echoes the finding that the models are not taking into account a potentially important major driver of warming or an important feedback loop. The implications for climate projections are uncertain. On the one hand, if the models are missing a key feedback loop, and that mechanism is relevant today, that could result in underprediction of warming. On the other hand, if the models are accurately predicting current climate responses without including an important causative factor, it may mean that the linkage between CO2 and warming is being over-modeled and over-sold.

Climate modeling is far from a precise science. The last decade of global temperatures (from about January 1999 onward) reveals little to no warming. This runs contrary to the estimates of most runs of climate models – though similar periods without warming do occur in a small portion of climate model runs, which include a statistically random element to account for typical small-scale variability. While a decade is a relatively small period in climate time-scales, this too points to the need to continue to research climate drivers.

We need to continue to discuss appropriate responses to climate change, but it is inappropriate to claim that the science is settled and all the facts are in. Estimates of the costs of climate change are even more uncertain – making it difficult to make reasonable decisions on the basis of these cost projections. The dialogue over climate change policy should continue, with an open acknowledgement that there are still many uncertainties in our understanding.

Amy Kaleita, Public Policy Fellow, Environmental Studies, Pacific Research Institute

copyright 2009 PRI

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