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Your article worries that hydrogen-fuel leakage may add to stratospheric ozone problems. Doesn’t that presuppose that the hydrogen for fuel is generated from a fossil source? What if the hydrogen is generated from air, seawater, or biomass?

Clark Waite
Descanso, Calif.

The source of the extra hydrogen molecules doesn’t matter, says geochemist John M. Eiler of the California Institute of Technology. It’s the concentration of atmospheric hydrogen that moisturizes the high-altitude air, which in turn drives the ozone-destroying chemical reactions .–S. Perkins In the short article, the words “might,” “could,” and “may” appear frequently. Whatever happened to the use of the words such as “will” and “won’t” by scientists, economists, and environmentalists?

James Hendry
Florissant, Mo.