Number 12 (Story #3), December 10, 1990 by Phillip F. Schewe and Ben Stein WORLD CLIMATE CHANGE: Scientists participating in the Intergovernmental Panel on Climate Change (IPCC) summarized some of their findings at the AGU meeting (and in a report distributed there). The IPCC scientists "are certain" that "there is a natural greenhouse effect which already keeps the Earth warmer than it would otherwise be" and that emissions from human activities "will enhance the greenhouse effect, resulting on average in an additional warming of the Earth's surface." The IPCC "calculates with confidence" that "carbon dioxide has been responsible for over half the enhanced greenhouse effect in the past, and is likely to remain so in the future." "Based on current model results," they predict that under a business-as-usual scenario, a "likely increase in global mean temperature of about 1 degree C above the present value by 2025 and 3 degrees C before the end of the next century" will occur, along with a rise of about 20 cm in global mean sea level by 2030. The IPCC report notes, however, that the anticipated greenhouse effects may be of roughly the same size as the natural variability of past temperature patterns and that "unequivocal detection of the enhanced greenhouse effect from observations is not likely for a decade or more. (William Sprigg, NOAA, 202-673-5360.)