Storyline description of Southern Hemisphere midlatitude circulation and precipitation response to greenhouse gas forcing

Abstract

As evidence of climate change strengthens, knowledge of its regional implications becomes an urgent need for decision making. Current understanding of regional precipitation changes is substantially limited by our understanding of the atmospheric circulation response to climate change, which to a high degree remains uncertain. This uncertainty is reflected in the wide spread in atmospheric circulation changes projected in multimodel ensembles, which cannot be directly interpreted in a probabilistic sense. The uncertainty can instead be represented by studying a discrete set of physically plausible storylines of atmospheric circulation changes. By mining CMIP5 model output, here we take this broader perspective and develop storylines for Southern Hemisphere (SH) midlatitude circulation changes, conditioned on the degree of global-mean warming, based on the climate responses of two remote drivers: the enhanced warming of the tropical upper troposphere and the strengthening of the stratospheric polar vortex. For the three continental domains in the SH, we analyse the precipitation changes under each storyline. To allow comparison with previous studies, we also link both circulation and precipitation changes with those of the Southern Annular Mode. Our results show that the response to tropical warming leads to a strengthening of the midlatitude westerly winds, whilst the response to a delayed breakdown (for DJF) or strengthening (for JJA) of the stratospheric vortex leads to a poleward shift of the westerly winds and the storm tracks. However, the circulation response is not zonally symmetric and the regional precipitation storylines for South America, South Africa, South of Australia and New Zealand exhibit quite specific dependencies on the two remote drivers, which are not well represented by changes in the Southern Annular Mode.

More meteorological events that drive compound coastal flooding are projected under climate change

“…Overall, we are confident that the above limitations do not distort our findings and that our study expands the understanding of present and future global compound flooding hazard. This is supported by the fact that our findings are physically consistent with studies of large-scale atmospheric circulation changes employing larger model ensembles than the present one 5,44,45,46,47,48,68,69 .…”

“…4c) is consistent with a poleward shift in the north Pacific boreal winter jet stream and in the associated stormtrack 44,46,47 . A similar poleward shift of the storm track 46,48 appears consistent with the projected changes in joint return period for New Zealand, southern Australia, and southern South America (Fig. 4c).…”

Combined Effects of Global Warming and Ozone Depletion/Recovery on Southern Hemisphere Atmospheric Circulation and Regional Precipitation

“…The goal of this study is to extend the approach of Mindlin et al. (2020) to include the effect of both global warming and ozone depletion/recovery on the SPV breakdown, and thereby on regional SH climate, testing the hypothesis of the “tug‐of‐war” occurring in the stratosphere. We do this by taking into account both drivers of the SPV breakdown delay together with tropical upper‐tropospheric warming, and constructing time‐dependent storylines for SH circulation and regional precipitation changes associated with different responses of the remote drivers to anthropogenic forcings.…”

Water Resources Change in Central-Western Argentina Under the Paris Agreement Warming Targets

“…This expansion may have also favored the southward shift of the storm tracks and the consequent decline in seasonal and annual precipitation over the Andes region. Possible causes behind this tropical expansion were attributed mainly to increased GHG emissions and ozone depletion effects and, to a lesser extent, to internal climate variability (Staten et al, 2018;Villamayor et al, 2019;Mindlin et al, 2020). The black line represents the ensemble mean for the historical runs, the shading in gray indicates the 5 and 95% quantiles across the historical model runs.…”

“…These observed changes in the precipitation patterns and its implications for the hydrological cycle components it the CWA region have been linked to changes in large-scale atmospheric circulation induced by increased greenhouse gases (GHG) emissions and ozone depletion (Staten et al, 2018;Villamayor et al, 2019;Mindlin et al, 2020). In particular, the poleward expansion of the Hadley Circulation has been attributed to play a significant role in the observed long-term precipitation decline along South-Western South America.…”