Ozone hole and Southern Hemisphere climate change

Abstract

[1] Climate change in the Southern Hemisphere (SH) has been robustly documented in the last several years. It has altered the atmospheric circulation in a surprising number of ways: a rising global tropopause, a poleward intensification of the westerly jet, a poleward shift in storm tracks, a poleward expansion of the Hadley cell, and many others. While these changes have been extensively related with anthropogenic warming resulting from the increase in greenhouse gases, their potential link to stratospheric cooling resulting from ozone depletion has only recently been examined and a comprehensive picture is still lacking. Examining model output from the coupled climate models participating in the Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment (AR4), and grouping them depending on the stratospheric ozone forcing used, we here show that stratospheric ozone affects the entire atmospheric circulation in the SH, from the polar regions to the subtropics, and from the stratosphere to the surface. Furthermore, model projections suggest that the anticipated ozone recovery, resulting from the implementation of the Montreal Protocol, will likely decelerate future climate change resulting from increased greenhouse gases, although it might accelerate surface warming over Antarctica. [2] Recent studies have shown that, in the late 20th century, depletion of stratospheric ozone by anthropogenic halogen compounds has affected the SH surface climate by forcing sea-level-pressure (SLP) to decrease in high latitudes and to increase in mid latitudes [Thompson and Solomon, 2002;Marshall, 2003]. This dipolar SLP change, which is robustly found in climate model integrations [Gillett and Thompson, 2003;Shindell and Schmidt, 2004;Miller et al., 2006;Arblaster and Meehl, 2006;Cai and Cowan, 2007], is qualitatively similar to the so-called Southern Annular Mode (SAM) [Thompson et al., 2000], and intimately related to the latitudinal position of the midlatitude jet [Thompson et al., 2000;Son et al., 2008]. While this suggests that stratospheric ozone plays an important role in controlling tropospheric circulation [e.g., Gillett and Thompson, 2003], its detailed impact on the various components of the SH climate system, from the polar regions to the subtropics, remains unclear at present. This question is especially pertinent in view of the predicted recovery of stratospheric ozone [e.g., Eyring et al., 2007] which, as a result of the implementation of the Montreal Protocol, is expected to occur in the next 50-60 years.[3] In this study, we demonstrate the pervasive impacts of stratospheric ozone on SH climate change by examining output from the IPCC/AR4 models [Meehl et al., 2007]. Both past (20C3M) and future scenario integrations with moderate greenhouse-gas forcing (A1B) are analyzed, ozone forcing being the key discriminating factor among the models. As indicated in Table 1, not all IPCC/AR4 models included ozone depletion and recovery [Miller et al., 2006;Cai and Cowan, 2007;Karpechko et al., 2008;Son et al., 2008...

An assessment and interpretation of the observed warming of West Antarctica in the austral spring

“…We note that our interpretation that SSTs have played a role in forcing Antarctic climate change is not necessarily at odds with interpretations that focus on the role of stratospheric ozone depletion (e.g. Thompson and Solomon 2002;Perlwitz et al 2008;Son et al 2009). Our assessment underscores that temperatures across East Antarctica have not changed significantly, and have even cooled slightly in austral summer and autumn (though no significantly so) since 1979.…”

“…While the projected gradual recovery of the ozone hole is likely to be an important driver of 21 st Century Antarctic climate change in general (e.g. Perlwitz et al 2008;Son et al 2009), regional predictions of West Antarctic climate change will need to take into account low-latitude SST and regional sea ice changes. Our results point to the need for future observational and modeling studies to focus on the regional and seasonal characteristics of Antarctic climate change, the regional response to ozone depletion, the influence of tropical variability and climate change on Antarctic climate, and on the mechanisms that link sea ice and air temperature in Antarctica.…”

Changes in the width of the tropical belt due to simple radiative forcing changes in the GeoMIP simulations

“…Any climate forcing that modifies mean temperatures or their gradients could thus drive variations in the tropical belt width. Stratospheric ozone depletion and its resulting polar stratospheric cooling have been argued to be a potentially dominant driver of Southern Hemisphere tropical expansion (Polvani et al, 2011b;Min and Son, 2013), and ozone recovery over the coming decades may oppose any future greenhouse-gas-driven expansion (Son et al, 2009;Polvani et al, 2011a). Black carbon, tropospheric ozone (Allen et al, 2012), and aerosols (Allen and Sherwood, 2011;Allen et al, 2014) may have also played a role in historical tropical expansion, especially in the Northern Hemisphere.…”

Antarctic ozone variability inside the polar vortex estimated from balloon measurements

“…Recent studies based on coupled chemistry-climate models have shown that stratospheric ozone affects the whole atmospheric circulation in an unexpected number of ways (Son et al, 2009). For instance, ozone depletion seems to have contributed to increasing the Southern Annular Mode (SAM) index (Thompson and Solomon, 2002;Arblaster and Meehl, 2006), poleward shifting of the westerly jet in midlatitudes and increasing global tropopause height (Santer et al, 2003).…”