Contact: Dane Konop                               FOR RELEASE      
                                                 11/21/97

Is the Earth warming, how is humankind contributing, and what will be the consequences? These and other important questions are answered by J. D. Mahlman, director of the National Oceanic and Atmospheric Administration's Geophysical Fluid Dynamics Laboratory in Princeton, N.J. , writing in the Nov. 21 issue of Science.

Mahlman succinctly summarizes the current climate debate, sorts out the various principal predictions of future climate, and rates the confidence level of these predictions on a scale from "virtually certain facts" to "incorrect projections."

According to Mahlman, some virtually certain facts include: Greenhouse gases, which warm the planet, are increasing. These gases affect the climate for many centuries after they enter the atmosphere. Human-caused increases in carbon dioxide and decreases in ozone in the stratosphere have already resulted in a 1 degree Celsius average cooling there. Over the past century, the Earth's surface has warmed about .5 degrees Celsius.

Some very probable projections (greater than 9 out of 10 chance of being true)
include: A doubling of carbon dioxide in the atmosphere over pre-industrial levels in the next century will lead eventually to an average warming of from 1.5 to 4.5 degrees Celsius. By 2100, average sea level could rise 25-75 centimeters.

Some probable projections (greater than 2 out of 3 chance of being true) include: Models project marked decreases in soil moisture in response to increases in summer temperatures over northern mid-latitude continents. Tropical storms, once formed, might tend to become more intense.

Some incorrect projections include: The number of tropical storms, hurricanes and typhoons per year will increase. (Mahlman says there is no credible evidence for this.) Winds in mid-latitude, versus tropical, cyclones will become more intense. (Mahlman notes it is theoretically plausible that smaller-scale storms such as thunderstorms or squall lines could become stronger under locally favorable conditions, but the direct evidence remains weak.)

Although we cannot yet produce a sharp picture of future climate, either globally or locally, Mahlman points out that none of these known uncertainties will make the problem of human-induced greenhouse warming go away. It is virtually certain, he concludes, that this warming will continue for a long time and that the severity of impacts from a changed climate depend on resolving uncertainties in the climate system and in our success in reducing emissions of greenhouse gases.

For more information about climate change, visit the Geophysical Fluid Dynamics Laboratory web page at www.gfdl.gov/gfdl_research.htm. All NOAA press releases and links to other NOAA material can be found on the Internet at http://www.noaa.gov/public-affairs. Journalists who wish to be added to NOAA's press release distribution list, or who wish to switch from fax to e-mail delivery, can send an e-mail to releases@www.rdc.noaa.gov, or fax (202) 482-3154.