Global Warming Study Remains Educated Guess New Look at the `Greenhouse' Effect Still Says Earth Gets Hotter Climate and Higher Sea Level

Article excerpt

FOR prophets of global warming, forecasting remains an "iffy" business.

They know people are perturbing the climate system with heat-trapping "greenhouse" gases. Yet their computer simulations still yield only "best guesses" as to what the effects may be.

This uncertainty permeates a new attempt to project future climate using material prepared for the United Nations Conference on Environment and Development now under way in Rio de Janeiro. The new study reduces a 100-year projection of global warming and sea level rise by the Intergovernmental Panel on Climate Change (IPCC) in 1990. Yet it warns that humanity still faces possibly serious climate change. The first study

An IPCC team of 170 scientists from many countries based the 1990 projections on a variety of scenarios for future emissions of carbon dioxide (CO2) and other greenhouse gases. The IPCC has refined those scenarios for the Rio conference. Tom Wigley and Sarah Raper of the Climate Research Unit at the University of East Anglia in Norwich, England, have used the new scenarios to reforecast warming and sea-level changes.

Reporting their work recently in Nature, Drs. Wigley and Raper note that the earlier IPCC "best guess" projected a 3.3 degree C rise in average global temperature and a 66 centimeter rise in sea level. Their new "best guess" is for a 2.5 degree warming and 48 centimeter sea level rise. Warnings remain

Wigley and Raper point out that while "these are substantial reductions ... the projected changes ... still are very large." They emphasize that "the warming corresponds to a rate roughly five times that observed over the past century and the sea level rise is at a rate roughly four times that estimated for the past century." Yet they also caution that "the uncertainty ranges for these projections are large, and they are higher ... than in" the 1990 forecasts.

Thus, one of the latest and most detailed computer simulations still fails to clear the climatologists' crystal ball.

That does not mean that climatologists have no certain knowledge. They understand very well how the greenhouse effect works and what kind of jolt greenhouse gas pollution is giving it.

Like a thrifty household, the climate system sticks to an energy budget in which income balances outgo in the long run. The Sun supplies the energy income. Clouds, bright surfaces, and aerosols reflect about 70 percent of incoming sunshine away from the planet. The other 30 percent - the energy income - is absorbed to drive the weather. …


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