Most people are under the impression global warming has risen by about 0.8 degrees C since the dawn of the industrial age. Unfortunately, mean temperatures have risen much further when account is taken of the short-term masking effect of aerosols emitted from coal and oil, mainly sulphur dioxide and its oxidized products. Moreover, since 2005 (the last year on which the IPCC-2007 report is based) Arctic Sea ice melt has resulted in lowering of the Earth reflectance of solar radiation back to space. As sea ice melts, exposure of open water to solar radiation results in the absorption of thermal infrared radiation and thereby further warming of the oceans.
Thus, according to the IPCC AR4-2007 report (figure SPM.2), the total anthropogenic greenhouse effect since 1750 AD, which is equivalent to about +2.3 degrees C, is masked by a compensating aerosol albedo effect equivalent to about -1.1 degrees C. However, given the short-lived residence time of sulphur aerosols in the atmosphere, this masking effect dissipates within periods up to a few years.