Polar Climate Change as Manifest in Atmospheric Circulation

Abstract

Purpose of review: Dynamic manifestations of climate change, i.e. those related to circulation, are less well understood than are thermodynamic, or temperature-related aspects. However, this knowledge gap is narrowing. We review recent progress in understanding the causes of observed changes in polar tropospheric and stratospheric circulation, and in interpreting climate model projections of their future changes.

Recent findings: Trends in the annular modes reflect the influences of multiple drivers. In the Northern Hemisphere, there appears to be a "tug-of-war" between the opposing effects of Arctic near-surface warming and tropical upper tropospheric warming, two predominant features of the atmospheric response to increasing greenhouse gases. Future trends in the Southern Hemisphere largely depend on the competing effects of stratospheric ozone recovery and increasing greenhouse gases.

Summary: Human influence on the Antarctic circulation is detectable in the strengthening of the stratospheric polar vortex and the poleward shift of the tropospheric westerly winds. Observed Arctic circulation changes cannot be confidently separated from internal atmospheric variability.

Keywords: Annular modes; Antarctic; Arctic; Climate change; Cyclones; Stratospheric polar vortex.

Fig. 1

Indices of the Northern Annular Mode (left) and Southern Annular Mode (right) from observations and models. The black line shows, for each season (top to bottom), the CMIP5 multi-model mean of historical and RCP4.5 simulations. The grey band shows the 5–95% confidence range based on the individual model simulations. The coloured lines show observational indices derived from HadSLP2 (red), NOAA-CIRES Twentieth Century Reanalysis (orange) and Japanese 55-year Reanalysis (blue). Simulated anomalies are shown relative to the 1861–1900 baseline, and observations are centred on the multi-model mean over the period for which they are shown. The symbols to the right of each line graph show changes between 1980–2029 and 2050–2099, for each individual model (black circles) and the multi-model mean (red line). Adapted from Gillett and Fyfe (2013), where further details on these data and methods can be found [34]