Late in the evaluation and modeling stage of the 2011 UNEP/WMO Integrated Assessment of Black Carbon and Tropospheric Ozone, researchers were surprised when newly-acquired IIASA numbers regarding measures for domestic heating — replacement of wood burning with pellets in OECD nations — led to about 15% greater cooling in the Arctic region. Indeed the UNEP Assessment showed a greater temperature response in the Arctic to SLCP measures than that of any other region, or in the globe as a whole.
Much of this greater response arises from the greater impact from black carbon (BC) emissions over the highly reflective surface of ice and snow. Black carbon researchers today also believe there is less uncertainty overall from sources that carry higher percentages of the more reflective, “white” organic carbon and “yellow” sulfates often co-emitted with black carbon from many sources, especially biomass burning. This is because the lighter organic carbon and sulfates reflect the sun’s rays and thus can actually cool more than black carbon from that same source might warm; but only over a surface that is darker to begin with. Such a “cooling” impact is absent over a surface that is already white and highly reflective, such as ice and snow.
Because these regions have reacted more strongly in general to global warming, showing an increase in temperature twice that of the global mean, they are also at greater risk. The 2-degree global limit set by the Copenhagen Accord translates into 4-5 degrees in most polar and alpine regions. The IPCC, Arctic Council and others estimate that such a rise in temperature will lead to feedback mechanisms speeding global warming further, chiefly by decreasing the overall reflectivity (albedo) of the globe and by leading to increased emissions of methane and CO2 from permafrost. The record sea ice melting and Greenland-wide melt of summer 2012 only underscores the vulnerability of all cryosphere regions.
SLCP reductions, if taken in concert with the CO2 reductions and in the same time frame, offer the best and perhaps only means easily available to slow this trend in the near-term, by the critical 2030-2050 time frame. At the same time, it is important from an economic and development perspective to ascertain which kinds of SLCP reduction measures provide the greatest climate, health and crop co-benefits so that the most effective measures can be targeted. This is especially the case for black carbon measures because they are highly regional in their impacts and dependent on regional factors such as wind direction and precipitation. Black carbon measures also have important impacts on other kinds of climate responses, especially seasonal precipitation patterns, most notably the Asian monsoon, but more detailed modeling may uncover other regional patterns as well.