More Heat Over Greenhouse Gases

The article “Warming Oceans Appear Linked to Atmospheric Greenhouse Gases” (Physics Today, June 2001, page 19 ) prompted a comment from Robert C. Whitten (Physics Today, December 2001, page 12 ). He stated “how the mean atmospheric temperature can remain essentially constant while warming the oceans is never explained.” In her response to Whitten, Barbara Goss Levi tells us that “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.” This reasoning is flawed for two reasons.

First, that the additional greenhouse gases absorb additional radiation from Earth’s surface implies that warming will obviously occur where the additional gases are located, assuming they are at a lower temperature than Earth’s surface. This assumption will normally be satisfied. Indeed, the original article by Levi states, “If the trapped infrared radiation is heating the atmosphere, we might expect it to be warming the world’s oceans as well.” While this statement is correct, the response to Whitten contradicts it.

Second, if we were to accept the erroneous explanation that reradiation from the greenhouse gases warmed only the ocean surface, then we would have difficulty explaining why this warmer ocean did not transfer some of the added heat to the surface air layer in contact with the ocean, thereby warming the atmosphere. It is well known that air passing over the ocean rapidly reaches thermal equilibrium with the water surface, and surface air temperatures normally maintain a value very nearly that of the ocean surface. This warming of the surface air would, in turn, be distributed upward, probably in a period of days, certainly not years, resulting in a mean temperature above what it would be without the greenhouse gases. Thus, in either scenario, a net warming of the troposphere would result. We thus conclude that there is no way that the ocean surface can warm without a resulting warming of the overlying atmosphere.