The Antarctic ozone hole and the pattern effect on climate sensitivity

Abstract

Since about 1980, the tropical Pacific has been anomalously cold, while the broader tropics have warmed. This has caused anomalous weather in midlatitudes as well as a reduction in the apparent sensitivity of the climate associated with enhanced low-cloud abundance over the cooler waters of the eastern tropical Pacific. Recent modeling work has shown that cooler temperatures over the Southern Ocean around Antarctica can lead to cooler temperatures over the eastern tropical Pacific. Here we suggest that surface wind anomalies associated with the Antarctic ozone hole can cause cooler temperatures over the Southern Ocean that extend into the tropics. We use the short-term variability of the Southern Annular Mode of zonal wind variability to show an association between surface zonal wind variations over the Southern Ocean, cooling over the Southern Ocean, and cooling in the eastern tropical Pacific. This suggests that the cooling of the eastern tropical Pacific may be associated with the onset of the Antarctic ozone hole.

Antarctic Ice‐Sheet Meltwater Reduces Transient Warming and Climate Sensitivity Through the Sea‐Surface Temperature Pattern Effect

“…However, the pattern of those trends becomes qualitatively closer to observations than that simulated without meltwater input. The underestimated Southern Ocean trends in the Hosing simulations may be caused by a too‐weak sensitivity to meltwater input in the model (Pauling et al., 2016) or a combined effect with other factors that have contributed to the observed Southern Ocean temperature trends, for example, the strengthening in the Southern Hemisphere midlatitude jet owing to the Antarctic ozone hole (Hartmann, 2022; Kostov et al., 2018). Overall, these results suggest that the lack of realistic Antarctic meltwater input in models may explain some of the model‐observation discrepancies in the Southern Ocean.…”

“…Model‐observation discrepancies in the recent historical record call into question our ability to accurately project future warming at both global and regional scales. While many recent studies have shown that the observed tropical SST trends and circulation changes could be influenced by various Southern Ocean forcings through teleconnections (Dong et al., 2022; Hartmann, 2022; Kang et al., 2020; Kim et al., 2022), here we examined the impact of anomalous Antarctic meltwater on tropical SST pattern effects and the global warming rate. Within two sets of meltwater hosing simulations performed using CESM1‐CAM5, we find that the transient global warming rate is reduced by Antarctic meltwater input, owing to both a stronger OHU efficiency and a stronger radiative feedback (corresponding to a lower effective climate sensitivity).…”

Intermodel spread in Walker circulation responses linked to spread in moist stability and radiation responses

“…In contrast, an ocean dynamical thermostat mechanism, changes in anthropogenic aerosols, and southern ocean cooling may contribute a strengthening of the zonal SST gradient with warming (Clement et al, 1996;Heede & Fedorov, 2021;Hartmann, 2022).…”

“…Further, analysis of changes in historical CMIP6 simulations from 1950 to 2014 suggests a relative cooling of the equatorial East Pacific due to changes in aerosols, contributing an initial strengthening tendency of the WC (Heede & Fedorov, 2021). Additionally, cooling of the southern ocean is linked with cooling of the tropical East Pacific, and may contribute to the observed strengthening of the zonal SST gradient (Hartmann, 2022).…”

Intermodel Spread in Walker Circulation Responses Linked to Spread in Moist Stability and Radiation Responses

“…In contrast, an ocean dynamical thermostat mechanism, changes in anthropogenic aerosols, and southern ocean cooling may contribute a strengthening of the zonal SST gradient with warming (Clement et al., 1996; Hartmann, 2022; Heede & Fedorov, 2021). The ocean dynamical thermostat mechanism, which was proposed using a highly idealized ocean model, describes a transient strengthening of the zonal SST gradient through (a) upwelling of relatively cool water in the equatorial East Pacific, thereby increasing the zonal SST gradient, and (b) increases in surface easterly winds which further increase this gradient (Clement et al., 1996).…”