An Aug. 16 Science Notebook story described an article in the journal Science about global warming and carbon dioxide emissions. A writer of that article said that if governments fail to act, the concentration of carbon dioxide in the atmosphere will triple in 50 years.

When reliable measurements of atmospheric carbon dioxide were first taken in Hawaii in 1958, the concentration was about 317 parts per million (ppm). Today it is 375 ppm, an increase of 18 percent in 45 years. The rate of increase has been remarkably constant, varying between 0.4 percent and 0.45 percent per year when calculated from 1958 through any of the past 10 years. The background concentration, before the Industrial Revolution, was 280 ppm.

Tripling the concentration in 50 years would require an immediate quadrupling of the rate of increase. The infrastructure to burn fossil fuel at these rates simply cannot be constructed in a quarter-century. As it was, the largest economic expansion in human history brought only an 18 percent increase in atmospheric carbon dioxide in the past half-century.

To change this number to 300 percent in the next half-century would be impossible.

PATRICK J. MICHAELS

Senior Fellow in Environmental Studies

Cato Institute

Washington