The Bizarre Antarctic: Why is the Radiative Forcing and Greenhouse Effect Negative?

Observed climatology indicates that the Antarctic strangely exhibits a negative greenhouse effect during fall and winter. Even more bizarre, during this same period of time the top-of-atmosphere (TOA) radiative forcing associated with an increase of carbon dioxide (CO₂) is negative, indicating an increase of CO₂ is actually cooling the earth-atmosphere system over the Antarctic. While a negative greenhouse effect is not always accompanied by a negative radiative forcing, the causes for both are the same. Using a recently developed saturation-level concept, we demonstrate that temperature controls the radiative saturation point, such that at long wavelengths with strong absorption, the upward longwave (LW) radiation follows the radiative saturation line closely. An increasing with height temperature profile would thus lead to a vertical upward LW flux profile that also increases with height. The unique vertical temperature profile during fall and winter in the Antarctic, which has a substantial increasing with height component in its temperature profile, thus leads to a negative greenhouse effect and radiative forcing.