Linkage between anthropogenic aerosols and winter extremes on the decadal time scale

The uncertainty of atmospheric aerosol effects on climate mainly stems from the inhomogeneous and fast varying spatial distribution of aerosols, and the complicated mechanisms of aerosol-radiation-circulation interactions. The historical changes in anthropogenic emissions of aerosols and precursor gases in the past few decades are characterized by a shift of pollution centers from the US and Europe to East and South Asia. Using long-term temperature record, reanalysis data, and global climate model simulations (NCAR CESM1&2), we perform attribution analyses on the variations of winter mean climate and extreme events in the northern hemisphere since the 1970s and explore the possible climatic impacts of the historical anthropogenic aerosol changes. We find the spatial pattern of modeled surface temperature changes induced by aerosol forcing resembles that from the leading component of the GISS surface temperature record in the wintertime northern hemisphere derived from empirical-orthogonal-function analysis. We also find the fingerprint of the transient aerosol forcing on the decadal trends of the meandering of the atmospheric flows in the mid-latitude. Moreover, the contribution of natural climate variability to the observed decadal trends is illustrated through their correlations with six major climate natural variability indices. The mechanism of aerosol effects on the wintertime jet stream in mid-latitudes will be discussed in the presentation. Our findings shed light on the significant role of aerosol forcing in altering the regional and global climate changes.