From Today's New York Times

To the Editor:

Re “Greening the Herds: A New Diet to Cap Gas” (news article, June 5):

Your article about reducing methane emissions from dairy cows is welcome because of the attention it draws toward the substantial contribution that both beef and dairy cattle make to global warming.

In stating that the heat-trapping ability of methane is 20 times that of carbon dioxide, however, your report significantly understates the size of the problem. That figure is based on the impact of methane over the next century.

If, however, as many climate scientists believe, lowering our impact on climate change within the next 20 years is necessary to avoid passing a point of no return after which catastrophe may become unavoidable, then methane is 72 times as potent at trapping heat as carbon dioxide. (The difference is due to the fact that methane breaks down much more rapidly than carbon dioxide.)

Given this potency, an 18 percent reduction in methane emissions from cattle isn’t going to be anywhere near enough to turn dairying or beef production into sustainable industries. Reducing the size of the national cattle herd is the only feasible solution.

Peter Singer
Geoff Russell
Barry Brook
Melbourne, Australia, June 6, 2009
The writers are, respectively, a professor of bioethics at Princeton University, an independent researcher in Adelaide, Australia, and professor of climate change at the University of Adelaide.