Modelling the Impact of Short-lived Climate Forcers on Arctic Climate

The Arctic is an important region of study for climate change, as it is warming at twice the rate of the global average, and it is a pristine environment sensitive to global anthropogenic activities. While reduction of CO2 emissions remains an important objective to reduce Arctic warming, understanding the impacts of short-lived climate forcers (SLCFs) on the Arctic has become important for policies that aim to mitigate climate change on shorter time scales. The Arctic Monitoring and Assessment Programme (AMAP) is a scientific body of the Arctic Council and has worked to quantify the impact of SLCFs on the Arctic climate and has published two 2015 reports on: “Black carbon and ozone as Arctic climate forcers” (AMAP, 2015a) and “Methane as an Arctic climate forcer” (AMAP, 2015b). These reports are intended to inform the Arctic Council nations, who have agreed to reduce SLCF emissions.

A substantial international modelling effort was involved in determining the Arctic climate effects from black carbon, organic carbon, sulphate, and ozone from different geographical and source sectors. Environment and Climate Change Canada (ECCC) has contributed to this effort, using the Canadian Atmosphere Model (CanAM) version 4.2, with a bulk aerosol scheme. There were four other models used as well, and the Arctic equilibrium surface temperature response was calculated by translating the independently diagnosed radiative forcings from each model through the use of sensitivity coefficients (Sand et al, 2016). It was found that the largest non-methane SLCF Arctic warming source was from East and South Asian domestic emissions, followed by Russian fire emissions, and that the Arctic was most sensitive per-unit-mass emitted to local emissions from Arctic nations (Sand et al., 2016). Methane was not included in the above study, due to its longer lifetime, however, separate model runs, which included ECCC’s coupled Canadian Earth System Model (CanESM2) using specified methane concentrations from 1850 to present day estimated that historically increasing methane (not including follow-on effects on ozone) has caused 0.58^oC increase in Arctic temperature (AMAP, 2015b).

The AMAP group is now beginning work on new model simulations for a 2021 report on SLCFs for the Arctic Council, utilizing updated climate models and a more integrated, multispecies approach. ECCC plans on using a newer version of the CanESM, a coupled model containing the Piece-wise Logarithmic Aerosol (PLA) scheme, and the Canadian Middle Atmosphere Model (CMAM) chemistry for ozone and methane. Model simulations will include a 1-year baseline run for model validation, and number of simulations whereby geographical regions and source sectors are masked out in order to determine their relative impact to the total Arctic change. Emissions and the version of the CanESM model are based on the 6^th Climate Model Intercomparison Project (CMIP6).

Both CanESM and other AMAP models will be evaluated in a consistent way, using a large number of global and Arctic observations. We plan to include data from monitoring networks, intensive campaigns, and satellite measurements. Monthly average chemical tracer concentrations from all AMAP models will be evaluated in the same way against these measurements, and comparison statistics will be published in future reports or articles.

References

AMAP Assessment 2015: Black carbon and ozone as Arctic climate forcers. Arctic Monitoring and Assessment Programme (AMAP), 2015a, Oslo, Norway. vii + 116, pp.47-52.

AMAP Assessment 2015: Methane as an Arctic climate forcer. Arctic Monitoring and Assessment Programme (AMAP), 2015b, Oslo, Norway. vii + 139, pp.91-106.

Sand, M., T. K. Berntsen, K. von Salzen, M. G. Flanner, J. Langner, D. G. Victor, Response of Arctic temperature to changes in emissions of short-lived climate forcers, 2016, Nature Climate Change Letters, 6, 286-290, doi:10.1038/NCLIMATE2880.