Why is Reducing Black Carbon Emissions so Important?

Black carbon, which is the strongest light-absorbing component of particulate matter, is a critical contributor to human-induced climate warming, especially in the Arctic.  Black carbon primarily influences the Arctic climate through two different mechanisms. First, when black carbon is in the air, it directly warms the Arctic atmosphere by absorbing solar radiation that would otherwise have been reflected to space.[1] Second, when black carbon is deposited on light-colored surfaces, such as Arctic snow and ice, it reduces the amount of sunlight reflected back into space. This process results in the retention of heat and ultimately contributes to accelerated melting of Arctic snow and ice. In fact, a recent study found that black carbon emitted from in-Arctic sources has five times the warming effect than black carbon emitted at mid-latitudes.[2] A primary reason for this is that a much higher fraction of within-Arctic black carbon emissions deposit on snow and sea ice than mid-latitude emissions.

In addition, black carbon is unique in that it typically only remains airborne for approximately a week, depending on weather conditions.[3] This short-term nature of black carbon emissions is important for several reasons.  First, because black carbon only stays airborne for a short period of time, black carbon concentrations are highest close to the source. For this reason it is important to not only consider the percentage of black carbon emissions from individual sources, but also the location of the emissions.  For example, even though black carbon emissions from the shipping sector only account for a small percentage of the emissions in the Arctic region, black carbon emissions from ships traveling through or near to Arctic sea ice are likely to have a greater effect per unit of emission those from land-based sources.[4]  Second, given the short lifetime of black carbon in the atmosphere, reducing black carbon emissions will have a more immediate effect on the warming of the Arctic than long-term air pollutants.

[1]  Arctic Monitoring and Assessment Programme (AMAP), AMAP Technical Report No. 4: The Impact of Black Carbon on Arctic Climate, at 60 (2011).

[2] Sand, M. et al., Arctic Surface Temperature Change to Emissions of Black Carbon Within Arctic or Midlatitudes, 118 Journal of Geophysical Research: Atmospheres 14, 7788-7798 (2013).

[3] Arctic Monitoring and Assessment Programme (AMAP), Summary for Policy-Makers: Arctic Climate Issues 2015, Short-lived Climate Pollutants, at 4 (2015).

[4] See Arctic Monitoring and Assessment Programme (AMAP), AMAP Technical Report No. 4: The Impact of Black Carbon on Arctic Climate, at 60 (2011).