According to NASA’s Goddard Institute of Space Science climate reports, global warming is already committed to a rise above two degrees. The magical two degrees ceiling determined by governments is only holding thanks to effective, if unintended, geo-engineering by sulphur dioxide emitted from industry, holding global warming to about half of what it would be otherwise.
Recent publications by Hansen and his research group
indicate the rise of atmospheric energy (heat) level due to greenhouse gases and land clearing are committed to +2.3 degrees (+3.1 Watt/m2), currently mitigated by the transient effect of sulphur aerosols and the cooling effect of the oceans.
Sulphur dioxide is emanated from coal, oil and the processing of minerals (breakdown of sulphides to produce copper, zinc, lead and so on), and from other chemical industries. It combines with water in the atmosphere to produce sulphuric acid, which (being heavier than air) condenses and settles to the ground within a few years.
Aerosols stay in the atmosphere and stratosphere on time scales ranging from hours to days and to years, depending on their grain size, chemistry and height in the atmosphere and on the physical state and temperature of the atmosphere at different altitudes and latitudes.
The aerosols are short-lived, i.e. on time scales of up to a few years, but since they are continuously emitted from industry the overall level is increasing as burning of fossil fuels is rising.
The continuing emission of sulphur aerosols in effect constitute a global geo-engineering process without which the atmosphere would warm by another 1.2 degrees (1.6 Watt/m2) above the present level, resulting in near-doubling of global warming (Figure 1
Had it not been for the cooling effect of the short-lived (a few years long) sulphur aerosols, the internationally agreed maximum temperature ceiling of two degrees would have been transcended.
Cleaning of aerosol emissions, required in some countries, would result in thinning of the aerosol shield and thereby further warming.
At present measured temperature rise since 1880 of approximately +0.8 degrees is lagging behind +1.1 degrees warming (mitigated by sulphur aerosols), mainly due to the buffering effect of the oceans. The temperature rise lag period is not known but has been estimated as 35 years
Whereas according to the IPCC AR4 (2007) mean global land/ocean temperature since 1880 has risen by about +0.8C, this translates to more than +4C rise in the polar region of northern Canada, Greenland and Siberia (Figure 2