Ozone Hole Recovery May Reshape Southern Hemisphere Climate Change

May 6, 2008

graphic showing ozone hole over Antarctica
Ozone hole over Antarctica. Credit: NASA

A study published in the April 26, 2008 issue of Geophysical Research Letters by researchers from the University of Colorado's Cooperative Institute for Research in Environmental Science (CIRES), the NOAA Earth System Research Laboratory, and NASA has found that a full recovery of the stratospheric ozone hole over Antarctica could modify climate change in the Southern Hemisphere. Climate simulations of the 21st century with the NASA coupled chemistry climate model were the main research tool of the study. These simulations utilized climate forcing scenarios for increasing greenhouse gas (GHG) concentrations [IPCC scenario A1b] and decreasing ozone-depleting substances [WMO/UNEP scenario Ab]. The model response to the ozone recovery by 2100 shows that tropospheric circulation changes during austral summer caused by ozone depletion between 1970 and 2000 almost reverse, despite increasing GHG concentrations. When results were compared with IPCC model simulations, the researchers found that the impact is consistent but the magnitude of the response is significantly underestimated in the IPCC models.

An increase of westerly winds during austral summertime and cooling of the interior of the Antarctica has been observed during the last 30 year, and was attributed to stratospheric polar ozone depletion during spring. The Montreal Protocol restricted production of ozone-depleting substances, starting in 1987. As levels decline over the coming century, scientists predict the ozone hole will recover completely by 2070. The impact of ozone recovery on surface climate had not been investigated so far. IPCC models used for the Fourth Assessment do not include interaction between stratospheric ozone chemistry and climate. Some simulations included an ozone recovery scenario, but such scenarios were not uniformly defined. Only recently was it possible to run a series of long simulations from 1950 to 2100 with chemistry climate models to investigate the impact of ozone recovery on climate. These model configurations still miss the coupling to an interactive ocean model.

The results of this groundbreaking research suggest that ozone recovery is an important climate forcing in the 21st century, which needs to be addressed in assessments of future climate change. Until recently, climate models including those used in the IPCC's fourth assessment – have not been able to account for the link between ozone chemistry and climate change. This research shows the importance of simulating the combined effect of stratospheric ozone changes and increasing greenhouse gases on surface climate. Because of its close link to surface westerly winds, the recovery of the Antarctic ozone hole could affect the climate of the Antarctica, Australia and other Southern Hemisphere continental areas. It will also affect the Antarctic sea ice, ocean circulation and uptake of CO2. Further research with chemistry climate models that are coupled to the ocean is necessary to determine the climate impacts of stratospheric ozone recovery.

Contact: Judith Perlwitz