Greenhouse Gases Warm Things Up

Goss-Levi Replies: In asserting that “there is no evidence for rising temperatures in the atmosphere above the boundary layer,” Robert Whitten is touching on a discrepancy between different measurements of atmospheric temperature trends: The temperatures above the boundary layer (that is, above roughly 3 km), as recorded by satellites, have not shown the same 0.25-0.4°C temperature rise seen over the past two decades in the low- to mid-troposphere (up to 8 km), as determined from land- and sea-based measurements. However, a National Academy of Sciences panel concluded in 2000 that “the warming trend in global-mean surface temperature observations during the past 20 years is undoubtedly real.” ¹ The panel also concluded that “the troposphere actually may have warmed much less rapidly than the surface from 1979 into the late 1990s, due both to natural causes [such as volcanic eruptions] and human activities” such as chlorofluorocarbon-induced ozone depletion, which cools the upper troposphere.

Whitten asks how the oceans can warm if the atmosphere does not. Additional greenhouse gases added to Earth’s atmosphere absorb infrared radiation emitted by Earth’s surface and reradiate part of it to the surface. This radiation can warm the surface directly without warming the atmosphere first.

Whitten’s assertion that attributing a rising ocean temperature to greenhouse house gases is “pseudoscience” seems to be a reaction to remarks by Tim Barnett (Scripps Institution of Oceanography) as reported in my story. Barnett used standard scientific techniques to test competitive explanations for the increased ocean heat content: Solar irradiance and/or geothermal heating could not explain the observed ocean changes, while warming due to greenhouse gases gave almost precisely the observed values. Attributing the warming to greenhouse gases was the logical conclusion.