In his March 22 Commentary article, “Leading a moooot stampede," Matthew Hoffman makes light of the proposition that "the flatulence of cattle contributes methane to the atmosphere, promoting global warming." Strange as it may seem, this statement is scientifically correct and not a joke. It has nothing to do with the clearing of tropical rain forests but with the action of anaerobic bacteria in the complicated stomach of the cow—a fact that has been common knowledge for many decades.

But cattle-raising is only one a many human-related contributors to atmospheric methane, along with rice paddies, landfills, oil and gas operations. As I pointed out in a 1971 paper in the international scientific journal Nature, human activities release as much as 50 percent of all methane, with the balance from various natural sources, mainly bogs and swamps. However, as population grows, it follows that methane concentration must increase. And it has now been found to do so—at a rate of 1 percent a year, twice as fast as carbon dioxide, the most important greenhouse gas.

There are two further points of policy significance:

• Efforts to limit greenhouse gases have concentrated on carbon dioxide from the burning of fossil fuels. But regardless of what one may think about the scientific reality of greenhouse warming, a balanced approach must also consider equally drastic controls on methane, which would soon become the most important greenhouse gas. I have yet to see a bill calling for a phase out of cattle.

• Methane has a long lifetime in the lower atmosphere. As already calculated in 1971, this long lifetime will allow it to percolate into the stratosphere, produce water vapor there under the influence of the strong ultraviolet radiation, and play a part in chemical reactions affecting the stratospheric ozone.

Politicians who have been clamoring for a complete phase out of chlorofluorocarbons (CFCs) may not like the scientific conclusion that human activities have been affecting stratospheric chemistry long before CFCs were invented.