Exploring the Sensitivity of Arctic Winter Climate to Aerosol Loading as Simulated in CMIP6

Using model output from the Radiative Forcing Model Intercomparison Project (RFMIP), endorsed by the sixth Coupled Model Intercomparison Project 6 (CMIP6), we investigated the impact of aerosols on the Arctic climate (averaged over the region north of 66°N) during winter. The average of these models shows that the present-day aerosols (as of the year 2014) result in a positive aerosol effective radiative forcing (ERF_aer) of approximately 0.14 W m^–2 in the Arctic during winter, relative to pre-industrial conditions defined as those of the year 1850. This positive ERF_aer is associated with enhanced aerosol loading through strong transport from Eurasia and adjoining regions, causing the Arctic region to warm by up to 1 K in the present-day compared to the pre-industrial conditions. The Arctic warming attributed to aerosols also significantly affects climate variability, particularly the Arctic Oscillation (AO). Present-day aerosols resulted in a positively skewed distribution of the Arctic Oscillation index (AOI) compared to the control simulation, reflecting a shift toward more frequent positive AO phases associated with negative sea level pressure (SLP) anomalies across the northern Atlantic, Pacific, and Eurasian regions, and positive SLP anomalies over northern North America. Additionally, the transient experiment, which includes time-varying aerosol emissions, is used to investigate the sensitivity of Arctic winter climate to the aerosol enhancement, based on low and high aerosol scenarios. During the high aerosol scenario, warming in near-surface air temperature (SAT) is concentrated over the Arctic region, reaching approximately 1 K, while less warming is simulated in the low aerosol scenario. The AOI distribution is positively skewed in both aerosol scenarios, indicating that changes in aerosol concentrations influence the AO. However, the skewness is weaker under the high aerosol scenario compared to the low aerosol case, suggesting that stronger aerosol forcing tends to stabilize the AO and limit its variability. Nevertheless, increased sensitivity of the AO to aerosol can lead to extreme weather, particularly warmer winters in the Arctic, in contrast to most of the Northern Hemisphere, regardless of the AO phase. Our analysis also suggests that aerosol enhancement contributes to a shift in the jet stream’s position. Furthermore, the lapse rate feedback (LRF), a contributor to the Arctic amplification, also shows an increase due to aerosol enhancement. This indicates that both the strength and magnitude of the LRF are sensitive to aerosol concentrations, which may further intensify Arctic warming/amplification.

The results have been published:
Al Hajjar, K., Dipu, S., Quaas, J., Linke, O. and Haustein, K. (2025) ‘Exploring the Sensitivity of Arctic Winter Climate to Aerosol Loading as Simulated in CMIP6’, Tellus B: Chemical and Physical Meteorology, 77(1), p. 20–40. Available at: https://doi.org/10.16993/tellusb.1885.