Rising concentrations of methane and carbon dioxide are creating a 'negative greenhouse effect' over parts of Antarctica, but as temperatures rise, the air becomes more humid, which could reverse this slight cooling effect. There is sex.
Greenhouse gases such as CO2 and methane heat the earth by capturing radiation from the earth's surface. However, in certain rare circumstances, there could be a cooling effect that radiates more heat from the warmer upper layers into space than the atmosphere traps nearby…
Source: www.newscientist.com