Is Global Warming Caused by Water Vapor?

How to think about the No. 1 greenhouse gas.

By Brendan I. Koerner

Posted Tuesday, Jan. 22, 2008, at 11:16 AM ET

Every week, you blather on and on about carbon dioxide and methane. Yet you never mention a single word about the most important greenhouse gas of all, water vapor, which accounts for 98 percent of the greenhouse effect. Doesn't this inconvenient truth wholly discredit your little global-warming charade?

Variations on this question appear in the Lantern's inbox every few days, occasionally accompanied by family-unfriendly slurs. For folks who doubt that human activity is causing global warming, citing water vapor's role in the greenhouse effect is a common retort. Though such enviroskeptics are technically correct to some extent, the water-vapor argument by no means proves that anthropogenic (i.e. man-made) global warming is a fiction.