"Manmade CO2 emissions are much smaller than natural emissions. However, the CO2 that nature emits (from the ocean and vegetation) is balanced by natural absorptions (again by the ocean and vegetation). Human CO2 emissions upsets the natural balance."
If it was perfectly balanced, we would never see the proportion of atmospheric CO2 change. Ever. However, if proxies are to be relied upon, the proportion of Co2 has been dropping for a long, long time, and more and more of the planet has frozen. There were no ice ages millions of years ago. There was no ice cap either.
Water vapor is the #1 greenhouse gas. Better stop watering your lawn and all those millions of acres of crops....
Climatology and Trends of U.S. Surface Humidity and Temperature
Climatological annual and seasonal dewpoint, specific humidity, and relative humidity maps for the United States are presented using hourly data from 188 first-order weather stations for the period 1961–90.
With extended datasets for the period 1961–95, trends in these same variables and temperature are calculated for each of 170 stations and for eight regions of the country. The data show increases in specific humidity of several percent per decade, and increases in dewpoint of several tenths of a degree per decade, over most of the country in winter, spring, and summer.
Locally, anthropogenic modification of the hydrological cycle may be more important. Within the conterminous United States, the U.S. Geological Survey has estimated that consumptive use of water in agricultural irrigation contributes 100 billion gallons of water per day to the atmosphere, compared with 2,800 billion gallons per day from evaporation and transpiration from surface water bodies, land surface, and vegetation (van der Leeden et al. 1990). In dry regions during the growing season, the ratio of consumptive use to natural evaporative sources may be greater, and it is possible that long-term increases in evaporation from irrigated fields may be large enough to influence the surface trends at some stations. Other confounding influences may affect the trends presented here. However, the spatial consistency of the trends leads us to speculate that they are not primarily due to local phenomena but represent regional, indeed national, increases in near-surface specific humidity.
That is a lot of water vapor. I don't see it taken much into account in any of the "big models" or the IPCC stuff. The report above says we are adding 100 billion gallons per day through agricultural irrigation, but we are really adding a total of about 160 billion gallons per day, in the USA (see videos below). 160/2,800 is a 5.7% increase of daily water vapor added to the air. We are increasing the daily amount of water added to the air by nearly 6%, over natural sources, in the US alone.
The US is an easy example because we have lots of data. But think of other places like China and India that are probably adding even more of the worst largest greenhouse gas.
The effect of our forcing water into the atmosphere is similar to changing the surface water of the planet from 70% to about 75%. It will have a sizeable effect on the earths temperature. Carbon dioxide is not a factor in these examples and I doubt that it is a major factor in global warming.
http://www.youtube.com/watch?v=e8Hdixpk-TQ
http://www.youtube.com/watch?v=ePLw6DyTYmI