While Earth's average surface temperatures have been increasing, the interior of Antarctica has been showing a unique cooling trend during the austral summer and autumn caused by ozone depletion, according to Judith Perlwitz of the Cooperative Institute for Research in Environmental Sciences, a joint institute of CU-Boulder and NOAA. "If the successful control of ozone-depleting substances allows for a full recovery of the ozone hole over Antarctica, we may finally see the interior of Antarctica begin to warm with the rest of the world," she added.
The scientists calculated that if ozone levels return to pre-1969 values, the low stratosphere over the South Pole will absorb more ultraviolet radiation from the Sun, effectively heating up this region. They also showed that ozone hole recovery would weaken the intense westerlies that circulate around Antarctica. These winds would no longer protect the area, exposing it to the warmer masses of air circulating above nearby continents and oceans.
If correct, the model also predicts that the entire southern hemisphere could be affected by these changes in wind circulation patterns. Indeed, previous studies have shown that such changes are associated with cooler temperatures over much of Australia and increased rainfall over the southeast Australian coast. In contrast, South American countries, including Argentina, Brazil and Paraguay, could experience drier conditions in spring and summer.
Perlwitz and colleagues obtained their results using a NASA supercomputer model that includes interactions between the climate and weather near the Earth's surface. The researchers ran the model from the 1950s to the end of the 21st century. For the past, they forced the model with observed changes in ozone-depleting substances and increased greenhouse gases. For the future, they followed specific scenarios from the World Meteorological Organisation (WMO) for ozone-depleting substances and Intergovernmental Panel on Climate Change (IPCC) figures for projected greenhouse gas emissions.
Although Perlwitz and co-workers assumed that greenhouse gases are going to increase, they also supposed that the amount of ozone-depleting substances in the atmosphere will decrease. The scientists also investigated changes in polar temperatures in the atmosphere and changes in westerly winds in the atmosphere and at the Earth's surface.
"On the basis of these results, we stress that including stratospheric processes in climate assessments will be crucial for accurate simulations of future climate change," Perlwitz told environmentalresearchweb. "This is the first time that a model has included interactions between the climate and stratospheric ozone chemistry."
The team points out that other climate models, including those used in the IPCC's fourth assessment, have not accounted for ozone chemistry. What’s more, most models do not extend beyond 30 kilometres above the Earth's surface – adequate representations of the stratosphere require modelling up to at least 60 km.
The researchers now plan to investigate the impact of ozone recovery on near-surface temperature and precipitation. "A more long-term goal is to couple the atmospheric chemistry climate model to an ocean model," revealed Perlwitz. "Such simulations have not been carried out so far because they take a lot of computing time."
The work was reported in Geophysical Research Letters.