It is alarming to hear Franklin Kameny {"Changed Climate Is Not Bad," letters, Aug. 19} give such a sunny assessment of the greenhouse effect. According to Mr. Kameny, the changes in climate resulting from the greenhouse effect are not to be dreaded: "Changed climate is not bad; it is just different." In his view, humans must simply adapt themselves to changing climatic circumstances.

One really must wonder if Mr. Kameny has not already spent too much time in the sun. While it is true that the Earth's climate has changed continually over its 5-billion-year history, these changes have been extraordinarily gradual, each change occurring over thousands of years. The fact of the matter is that human beings, through the indiscriminate burning of fossils fuels, are changing the world's climate in the space of only 100 years. Few would argue, as Mr. Kameny does, that these human-induced changes are beneficial.

Over the years, scientists have amassed considerable data on Venus, the nearest planet to Earth. They have learned that Venus suffers from a serious case of the greenhouse effect. Sunlight hits Venus, but the greenhouse gases in that planet's atmosphere prevent much of the heat from being radiated back into space. One result is that the average temperature on Venus is about 600 degrees Fahrenheit.

The bottom line is that the industrial nations of the world have a choice: we can continue to ply the atmosphere with carbon dioxide and pass on a much less livable world to our grandchildren, or we can reassess the ecological thresholds of our planet and make an effort to live with them. Climatic change should not be a matter of indifference.

DANIEL J. JOURDAN

Arlington