During the past decades, annual average temperatures in the Arctic have been rising almost twice as fast as in the rest of the world. Although the main driver of warming is the global increase in carbon dioxide concentrations, other climate forcers and feedback processes have a significant role in amplifying Arctic warming.
New research led by Nagoya University has found that black carbon (BC) aerosols are one of the main drivers of accelerated Arctic warming.
Black carbon is emitted in the atmosphere by fossil fuel combustion and biomass burning, absorbing solar radiation and heating the atmosphere. When deposited on snow and ice, black carbon can reduce their reflectivity and accelerate their melting.
In order to assess the impact of black carbon emissions on Arctic warming, an international team of scientists measured vertical profiles of BC mass concentrations up to 5km high in the Arctic in March and April 2018, during the Polar Airborne Measurements and Arctic Regional Climate Model Simulation Project (PAMARCMiP). The researchers compared BC mass concentrations to those measured in 2008, 2010, and 2015.
The concentrations in 2018 were similar to those in 2010 (between 7 and 23 nanograms per cubic meter), and smaller than those from 2008 and 2015. These findings were consistent with biomass burning activities in those years: while in 2010 and 2018 biomass burning activity was relatively low, in 2008 and 2015 it was much higher.
“These results suggest that the year-to-year variation of biomass burning activities likely affected BC amounts in the Arctic troposphere in spring, at least in the years examined in this study,” wrote the study authors.
The scientists found that the atmospheric heating effects of black carbon in the Arctic were highest in spring, when the incoming solar radiation is increasing and the BC mass concentration is at its peak. Furthermore, slight changes in the timing of snow and ice melting can significantly influence the radiation budget in the Arctic.
Finally, global warming can increase biomass burning in mid- and high-latitudes and thus have a stronger impact on the amount of Arctic black carbon than previously thought.
The study is published in the journal Atmospheric Chemistry and Physics.