To the Editor:
"Concerns on Melting of Polar Ice Are Eased" (Science Times, Sept. 22) infers from models and data published by Douglas R. MacAyeal that Antarctic ice cap melting may be so slow that we need not worry about sea-level rise. That study is reassuring only if one takes the short-term perspective of politicians in office. A longer point of view leads to very different conclusions.
Three questions are relevant: how quickly climate change takes place, how long it continues and its ultimate magnitude. By focusing only on the first, you give the impression that we need not worry about the other two. Ice melting, sea-level rise and global climate change may seem too slow to notice, but changes caused by excess greenhouse gases will take centuries to millenniums to play out because of the long time it takes ice caps to flow and deep ocean waters to warm.
You point out that sea levels 120,000 years ago were some 20 feet higher than today. The rise took place when temperatures were only about 2 degrees Fahrenheit warmer (less than values forecast for the next generation). That is far more than the foot-or-so rise for which economists are estimating damages, and policy makers are devising contingency plans.
Carbon dioxide concentrations in the atmosphere 120,000 years ago, with higher temperatures and sea levels, were 27 percent lower than now. We may anticipate much larger changes after carbon dioxide increases 100 percent or more. The Netherlands and other low-lying countries hope to raise dikes by several feet in the next decades at a cost of billions of dollars. This may give only temporary relief and need to be repeated generation after generation for centuries. THOMAS J. GOREAU President Global Coral Reef Alliance Chappaqua, N.Y., Sept. 24, 1992