Überraschend: Ozonloch beeinfusst Erdklima

Viel wurde in den letzten 20 Jahren über das Ozonloch diskutiert, das 2017 überraschend klein war. Ozonloch und Klimwandel sind dabei zwei verschiedene Themen. Trotzdem gibt es Berührungspunkte, denn das Ozonloch scheint auch das Klima zu beeinflussen. Bitz & Polvani 2012 berichteten einen Fall aus der Antarktis, wo die stratosphärische Ozonausdünnung offenbar zu einer Erwärmung der Landoberfläche und zur Meereisschmelze führt:

Antarctic climate response to stratospheric ozone depletion in a fine resolution ocean climate model
We investigate the impact of stratospheric ozone depletion on Antarctic climate, paying particular attention to the question of whether eddy parameterizations in the ocean fundamentally alter the results. This is accomplished by contrasting two versions of the Community Climate System Model (version 3.5), one at 0.1° ocean and sea ice resolution and the other at 1° with parameterized ocean eddies. At both resolutions, pairs of integrations are performed: one with high (1960) and one with low (2000) ozone levels. We find that the effect of ozone depletion is to warm the surface and the ocean to a depth of 1000 m and to significantly reduce the sea ice extent. While the ocean warming is somewhat weaker when the eddies are resolved, the total loss of sea ice area is roughly the same in the fine and coarse resolution cases.

In eine ähnliche Richtung geht eine Studie von Son et al. 2013, die sogar eine Klimabeeinflussung der gesamten südlichen Hemisphäre annehmen:

Improved seasonal forecast using ozone hole variability?
Southern Hemisphere (SH) climate change has been partly attributed to Antarctic ozone depletion in the literatures. Here we show that the ozone hole has affected not only the long-term climate change but also the interannual variability of SH surface climate. A significant negative correlation is observed between September ozone concentration and the October southern annular mode index, resulting in systematic variations in precipitation and surface air temperature throughout the SH. This time-lagged relationship is comparable to and independent of that associated with El Niño-Southern Oscillation and the Indian Ocean Dipole Mode, suggesting that SH seasonal forecasts could be improved by considering Antarctic stratospheric variability.

Wieder ein Jahr später dann eine Arbeit von Previdi & Polvani (2014) zum selben Thema:

Climate system response to stratospheric ozone depletion and recovery
We review what is presently known about the climate system response to stratospheric ozone depletion and its projected recovery, focusing on the responses of the atmosphere, ocean and cryosphere. Compared with well-mixed greenhouse gases (GHGs), the radiative forcing of climate due to observed stratospheric ozone loss is very small: in spite of this, recent trends in stratospheric ozone have caused profound changes in the Southern Hemisphere (SH) climate system, primarily by altering the tropospheric midlatitude jet, which is commonly described as a change in the Southern Annular Mode. Ozone depletion in the late twentieth century was the primary driver of the observed poleward shift of the jet during summer, which has been linked to changes in tropospheric and surface temperatures, clouds and cloud radiative effects, and precipitation at both middle and low latitudes. It is emphasized, however, that not all aspects of the SH climate response to stratospheric ozone forcing can be understood in terms of changes in the midlatitude jet. The response of the Southern Ocean and sea ice to ozone depletion is currently a matter of debate. For the former, the debate is centred on the role of ocean eddies in possibly opposing wind-driven changes in the mean circulation. For the latter, the issue is reconciling the observed expansion of Antarctic sea-ice extent during the satellite era with robust modelling evidence that the ice should melt as a result of stratospheric ozone depletion (and increases in GHGs). Despite lingering uncertainties, it has become clear that ozone depletion has been instrumental in driving SH climate change in recent decades. Similarly, ozone recovery will figure prominently in future climate change, with its impacts expected to largely cancel the impacts of increasing GHGs during the next half-century.

Interessant die Schlussfolgerung: Die Öffnung des Ozonlochs hat die Südhalbkugel erwärmt, während die nun einsetzende Schließung des Ozonlochs das Klima der Südhalbkugel abkühlt. Die Autoren gehen sogar davon aus, dass dieser Abkühlungsbetrag die durch CO2 berechnete Erwärmung in den kommenden 50 Jahren aufheben wird. Einige Studien wollten sogar den globalen Erwärmungshiatus des 21. Jahrhunderts und das erstarkende antarktische Meereis mit der Schließung des Ozonlochs erklären. Wiederum andere argumentieren, dass die Erwärmung des 20. Jahrhunderts eine Folge der höheren FCKW-Gehalte in der Atmosphäre war, und nicht so sehr mit dem CO2 zusammenhängt. Ob die Klimamodelle des IPCC all dies schon berücksichtigen? Vermutlich nicht, denn dann müsste die Erwärmungswirkung des CO2 reduziert werden…