TCS Daily

No Natural Paradox

By Sallie Baliunas - November 15, 2002 12:00 AM

The U.S. climate science community has been asked by the Bush Administration to help plan its research agenda for the next few years. The goal is to define, reliably, the human effect on global climate change resulting from anthropogenic emissions of, for instance, carbon dioxide, methane, aerosols and soot that would interfere with natural climate change. Present estimates of the human impact abound with uncertainty, and the objective of continued research is to reduce that uncertainty.

Despite the uncertainty of climate forecasts, calls have been made for reductions in human-made emissions. Only steep cuts would make a difference in the climate forecasts. But even accepting the uncertain temperature forecasts for the next 100 years, delaying deep cuts in emissions would result in extra warming of just a few tenths of a degree C above the middle-value forecasts of 2 - 3 C warming by 2100. The extra warming incurred by a delay in steep cuts would be much less than natural ups and downs in temperature.

Do We Know Enough to Act?

The question remains, do we currently know enough scientifically to justify large reductions in emissions? The tremendous research investment of about $20 billion dollars the U.S. has made since 1990 does not support rapid and intense cuts in anthropogenic emissions. Here are several reasons.

Major tools for forecasting the impact of the air's increased greenhouse gases are the highly complex climate simulations calculated on supercomputers. The simulations should be tested against measurements of recent and past climate. The output of computer simulations says that significant warming trends near the surface and in the low layer of air should already have occurred in the last few decades. But averaged over the globe, there has been only modest warming at the surface, and much of it predates the rise in the air's concentration of human-produced greenhouse gases. Very little warming has been seen in the low layer of air.

Also, the simulations expect a strong human-made surface warming trend at high latitudes - more pronounced than the global human-made trend. Yet the observed temperature trends at high latitude show little recent warming, contradicting the output of simulations. Thus the models erroneously exaggerate expected warming trends compared to measured trends.

Cloudy Science

In another case, the Third Assessment Report of the United Nations Intergovernmental Panel on Climate Change, issued in 2001, compares the average percentage of present-day cloudiness over the globe for December, January and February (p. 485 of Working Group I). The ten models give a range of output from 0% to around 90% average winter cloud coverage at high latitudes. Near the equator, the different models yield values ranging from 25% to 65% or so. Yet not one model agrees with the state-of-the art measurements from satellites.

Understanding cloud physics is critical to improving the models and their results. The climate has a natural greenhouse created predominantly by water in different forms - water vapor in the air, and water and ice droplets in clouds. Yet the climate effects of changes in water vapor and clouds remain poorly known.

Thus, a high priority for upcoming research should be targeted measuring programs lasting for several years in order to demystify the role of clouds and water vapor in climate change.

Good Work, More to Do

Since the UN report was written, researchers have continued to attack the unknowns in climate science - for example, with newly available measurements of the upper layers of air. Researchers at the University of Illinois and National Center for Atmospheric Research determined the air's temperatures at 30 to 110 km height, and found that the models give wrong results by as much as 20 degrees C (and different model results are equally wrong in opposite directions).

In science, conflict between predictions and measurements is progress. It serves to focus scientists' activities. This will take patient work, if science is to be the basis for deciding energy and environmental policy. According to the accumulated measurements, and even the exaggerated forecasts, time for study is available before making sharp emission cuts because temperature measurements do not show evidence for catastrophic human-made warming trends.

The climate simulations do not reproduce well-observed aspects of the climate system. To recognize that the forecasts of warming are deeply flawed while calling, on the basis of science, for intense cuts in carbon dioxide and other human-made emissions, makes for a paradox. Ultimately there are no paradoxes in nature. Any paradox is a signpost of ignorance - and a very valuable sign for scientists venturing into the unknown, where illumination comes only by science.



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