Tropospheric Temperatures

A trio of papers in the latest issue of Science magazine may well put to rest arguments that skeptics (and some politicians) have used to discount anthropogenic global warming. Most important is a paper by Carl Mears and Frank Wentz of Remote Sensing Systems, “The Effect of Diurnal Correction on Satellite-Derived Lower Tropospheric Temperature.”

The problem has been that, since 1990, an analysis of satellite observations showed the troposphere (the lowest few kilometers of the atmosphere) was warming too slowly compared to the surface for climate models to be correct. Needless to say, global-warming skeptics have seized on this result, saying that climate models had to be incorrect and therefore the view that mankind’s activities are warming the atmosphere must be in error.

“It has been the main crutch of the skeptics when it comes to pooh-poohing global warming, with some success,” says Kevin Trenberth, from the National Center for Atmospheric Research in Boulder, Colorado.

A group led by John Christy and Roy Spencer had earlier concluded that the troposphere was warming by about 0.09°C per decade, below what climate models predict. Mears and Wentz instead used a complicated model of the atmosphere to adjust the satellite measurements for time of day, and with it found that the troposphere appears to be warming by 0.19°C per decade, very close to surface measurements and climate models.

The Christy and Spencer group have admitted to an error in their earlier analysis, as Spencer wrote in a recent TechCentral Station article, and now they find a number of 0.12°C per decade. There’s still a slight discrepancy, but the argument has been moved along. As Spencer put it in TCS:

On the positive side, at least some portion of the disagreement between satellite and thermometer estimates of global temperature trends has now been removed. This helps to further shift the global warming debate out of the realm of “is warming happening?” to “how much has it warmed, and how much will it warm in the future?” (Equally valid questions to debate are “how much of the warmth is man-made?”, “is warming necessarily a bad thing?”, and “what can we do about it anyway?”.) And this is where the debate should be.