No Surface Cooling over Antarctica from the Negative Greenhouse Effect Associated with Instantaneous Quadrupling of CO2 Concentrations

Over the highest elevations of Antarctica, during many months of the year, air near the surface is colder than in much of the overlying atmosphere. This unique feature of the Antarctic atmosphere has been shown to result in a negative greenhouse effect and a negative instantaneous radiative forcing at the top of the atmosphere (RFTOA:INST), when carbon dioxide (CO2) concentrations are increased, and it has been suggested that this effect might play some role in te recent cooling trends observed over East Antarctica. Here, using fully coupled global climate model integrations, in addition to radiative transfer model calculations, the authors confirm the existence of such a negative RFTOA:INST over parts of Antarctica in response to an instantaneous quadrupling of CO2. However, it is also shown that the instantaneous radiative forcing at the tropopause (RFTP:INST) is positive. Further, the negative RFTOA:INST lasts only a few days following the imposed perturbation, and rapidly disappears as the stratosphere cools in response to increased CO2. As a consequence, like the RFTP:INST, the stratosphere-adjusted radiative forcing at the TOA is positive over all of Antarctica and, in the model presented herein, surface temperatures increase everywhere over that continent in response to quadrupled CO2. The results, therefore, clearly demonstrate that the curious negative instantaneous radiative forcing plays no role in the recently observed East Antarctic cooling.