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Impact of Anthropogenic CO2 and Other Greenhouse Gases from Climate since 1940, Including Water Vapor Feedback

Trenberth, Kevin 1
1 NCAR, Boulder, CO.

Increases in greenhouse gases cause global warming. This really means global heating of the planet. Carbon dioxide has increased about 38% since preindustrial times, and over half of this has occurred since 1970. It is responsible for about half of the total radiative heating increase, with the rest coming from increases in methane, nitrous oxide and changes in ozone. But about half is also estimated to be compensated for by increases in visible aerosol pollution that blocks the sun and causes cooling. The net effect is similar to the increase in carbon dioxide alone. Some of this heating goes into raising temperatures, while some goes into evaporating water and changing the hydrological cycle. The increased drying exacerbates droughts, heat waves and wild fires, and increases atmospheric water vapor. 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.


AAPG Search and Discovery Article #90090©2009 AAPG Annual Convention and Exhibition, Denver, Colorado, June 7-10, 2009