There is/was an interesting discussion paper at Atmospheric Chemistry and Physics, Black carbon in the atmosphere and snow, from pre-industrial times until present by R. B. Skeie, T. Berntsen, G. Myhre, C. A. Pedersen, J. Ström, S. Gerland, and J. A. Ogren, Its pretty much been tossed back for light revision, but is still available to read. The authors have modeled black carbon emissions and deposition on snow since 1750. There is great current interest in this, not only because of the direct climate forcing from black carbon, but also because black carbon deposited on snow or ice increases the absorption of sunlight and leads to faster melting.
While the modeling is approximate at best, and the observations even sketchier, the authors point to two obvious but interesting things. First, since 1960 burning of fossil fuels in the northern hemisphere has gotten a lot cleaner. North American BC emissions from fossil fuels and biofuels decreased by a factor of three between 1920 and 2000 and European emissions by a factor of two. Moreover, agricultural burning has decreased and forest fires are better controlled. Second, with the shift of industry to South and Southeastern Asia BC emissions and deposition have shifted towards the equator, meaning that less is deposited in the Arctic and that the contribution to ice melt is stable or decreasing. Taking one thing with another the paper asserts that the maximum for black carbon in the Arctic ice and snow was 1960.
According to the model, North American sources were responsible for approximately 80% of the BC deposited in Greenland snow in 1930. In year 2000 the contribution of BC deposited in 20 the snow has decreased to approximately 60% due to the decrease in North American emissions. . . .
The radiative forcing of BC impact on snow and ice maximizes in 1960, but only less than 20% higher than the RF in 1910. . . . In 1950 maximum values are found in the European and Russian sector of the Arctic Ocean and a secondary maximum is simulated over Europe. In 2000 the RF in the Arctic is reduced and the maximum over Europe is substantially reduced. Maximum values for year 2000 are found in the Himalayan region and the Tibetan plateau. . .
We find that the time evolution of the snow albedo effect is almost flat, with no significant increase in this forcing since early 20th century. Modelled BC burden in snow and ice and BC burden in the atmosphere north of 65 N reached its maximum in 1960, with a slight reduction thereafter. This indicates that the trend in the snow albedo effect has not been an important cause for the recent rapid warming in the Arctic. Yet, rejoice not too fast young bunnies, the shift in BC emissions to the south, has increased the forcing per unit emission by a quarter because of the aerosols can absorb more light in the tropics and be transported higher where there is more sunlight.
Posted by EliRabett at 7:19 PM