Many of the global warming hysterics claim that CO2 is the only cause of warming. It is man's fault they say. And when people point out that water vapor is the strongest greenhouse gas and it might be causing warming, they all shake their collective, consensus driven, sheeple heads and cluck their tongues about how denialists simply don't know what they are talking about.
But even the IPCC acknoweldges that water vapor is a bigger part of the greenhouse effect than CO2.
"Water vapour is the most important greenhouse gas, and carbon dioxide (CO2) is the second-most important one."
"Frequently Asked Question 1.3 What is the Greenhouse Effect?" source
Kenneth Trenbirth, a global warming advocate who is most famous for his comments in the hacked emails which said this:
"The fact is that we can't account for the lack of warming at the moment and it is a
travesty that we can't. The CERES data published in the August BAMS 09 supplement on 2008 shows there should be even more warming: but the data are surely wrong. Our observing system is inadequate." source
also said this:
"As atmospheric temperatures increase, the water-holding capacity of the atmosphere also increases, at a rate of about 4% per degree F. This is observed to be happening over the oceans, where surface water is not limited, and also to a slightly lower degree over land. Water vapor itself is a powerful greenhouse gas and roughly doubles the heating. The result is that global warming is “unequivocal” to quote the IPCC and is manifested not only in temperature increases throughout the atmosphere and ocean, but also through melting glaciers and ice sheets, rising sea level, melting Arctic sea ice, and changes in storms and hurricanes." Kevin E. Trenberth "Impact of Anthropogenic Carbon Dioxide and Other Greenhouse Gases on Climate since 1940, Including Water Vapor Feedback" Adapted from oral presentation at AAPG Annual Convention, Denver, Colorado, June 7-10, 2009 source
Basically, as the world warms, the atmosphere can hold more water vapor, which heats the earth further so it can hold more water vapor. If that happens, then the earth would warm because of WATER VAPOR, not CO2.
So, what is the history of water vapor in the atmosphere? The American Meteorological Society puts out a book each year, accessible from NOAA, which describes the state of the climate. The 2009 book, talking about 2008, had a really interesting chart of water vapor anomalies showing that over the past 20 years, up until 2007, the water vapor content of the atmosphere was increasing. Here it is from page S24 of the August 2009 supplement.
Clearly water vapor is increasing. In an article designed to shame the 'deniers' Slate author Brendan I. Koerner wrote:
"By mass and volume, water vapor is the most prevalent greenhouse gas in the atmosphere. According to both the International Panel on Climate Change and many global climate models, water vapor accounts for somewhere between 60 percent and 70 percent of the greenhouse effect. (The 98-percent figure, much beloved by global-warming skeptics, seems to have been first used in a 1991 article by Richard Lindzen. He cites a 1990 IPCC report as his source, but the report doesn't appear to contain that number.)
Brendan I. KoernerPosted "Is Global Warming Caused by Water Vapor?How to think about the No. 1 greenhouse gas." Tuesday, Jan. 22, 2008, at 11:16 AM ET Source
Ok, lets grant him 60%. Given that Wikipedia, a site carefully garded by global warming fanatics, claims that the average water content of the atmosphere is 25 mm source, the half a millimeter of additional water in the atmosphere represents a 3% rise in water vapor. By my calculations, that means that water vapor is accounting for more than half of the 'warming'.
Look at the world map of water vapor.
You can see that in 2008 the air was dry. There are no 'black' regions, but there are corresponding dark brown regions. That means that more long wave radiation can escape, which means that the earth will appear warmer to the satellites, but the earth will get cooler. Both things have happened. Last year was a cooler year, and I expect that when the August 2010 issue of BAMS comes out, 2009 will be even dryer.