Is “several degrees” of warming “virtually certain,” as NASA claims?

Earlier this week, at an American Geophysical Union meeting in San Francisco, NASA unveiled new data on atmospheric greenhouse gases (GHGs), notably carbon dioxide (CO2) and water vapor, from its Atmospheric Infrared Sounder (AIRS) unit on the agency’s Aqua spacecraft. NASA touted two main findings as “breakthroughs” in GHG research.

One supposed breakthrough is the discovery that CO2 is not “well-mixed” through the global troposphere (mid-level atmosphere), but is actually “lumpy” — distributed in higher concentrations in two “belts” circling the globe, especially in Northern hemisphere, which is more heavily industrialized. Now, I suppose this is a breakthrough in the sense that it will allow researchers to improve CO2 “transport models,” which hitherto have assumed that CO2 concentrations are uniform throughout the troposphere. But it would be surprising indeed if scientists did not know until now that industrialized regions have higher CO2 levels than non-industrialized areas.

The second supposed breakthrough is the claim that the AIRS data remove “most of the uncertainty about the role of water vapor [feedback]” in climate change.  “AIRS temperature data have corroborated climate model predictions that the warming of our climate produced as carbon dioxide levels rise will be greatly exacerbated — in fact, more than doubled — by water vapor,” said climate scientist Andrew Dressler of Texas A&M University. According to Dressler, “We are virtually certain to see Earth’s climate warm by several degrees Celsius in the next century, unless some strong negative feedback mechanism emerges elsewhere in the Earth’s climate system.” Dressler is talking about the assumption, common to all IPCC climate models, that the initial warming from rising CO2 levels increases concentrations of the atmosphere’s main greenhouse gas, water vapor, trapping more outgoing longwave (heat or infrared) radiation (OLR) and increasing global average rainfall.

William Gray of Colorado State University, perhaps the world’s leading hurricane forecaster, offers a different perspective on the NASA water vapor data. Gray’s comment follows:

I have just heard that NASA has a new satellite in orbit that can directly measure CO2 content in the atmosphere and that these new measurements are beginning to show that there is a positive association between increased rainfall (from higher CO2 gas amounts) and Outgoing Longwave Radiation (OLR) suppression. This is to be expected in and around the areas of precipitation — but not necessarily in global areas surrounding precipitation where return flow mass subsidence is driving the water vapor radiation emission level to a lower and somewhat warmer temperature.

I and a colleague, Barry Schwartz, have been analyzing 21 years (1984-2004) of ISCCP (International Satellite Cloud Climatology Project) outgoing longwave radiation on various space scales as related to precipitation differences. We have investigated how OLR changes with variations in precipitation from NOAA reanalysis data on time scales from 3 hours, a day, a month, and up to a year scale.

We find that on a small space scale where rainfall is occurring OLR is greatly suppressed. But on the larger regional to global scales, OLR rises with increasing precipitation. This is due to increased return flow subsidence in the surrounding cloud free and partly cloudy areas. Globally, we are finding that net OLR increases with net increased amounts of global precipitation. This is the opposite of what most GCMs [general circulation models] have programmed into their models and, if I’m interpreting the new NASA announcement correctly, opposite to what they are currently reporting to the media.

Dr. Gray presents a more detailed examination of these issues in his March 2009 Heartland Institute climate conference paper, available here.