Global warming doesn’t just change the weather, it also affects the ozone layer. According to a detailed new modelling study, by 2095 the springtime UV index (UVI) could go up by as much as 20% on the southernmost section of the planet, as altered atmospheric circulation pushes more stratospheric ozone into the Northern Hemisphere. That’s nearly half the UVI increase caused by ozone-eating pollutants in the late twentieth century – but coming from climate change alone.
In a study published in Nature Geoscience this week (subscription), Michaela Hegglin and Theodore Sheperd at the University of Toronto used the Canadian Middle Atomosphere Model, which fully resolves stratospheric circulation, to project ozone changes under the IPCC’s medium-emissions A1B scenario. As climate change unfolded, the model showed increased atmospheric upwelling in the tropics, and what went up in the tropical stratosphere came down disproportionately on Earth’s northern half. As a result, even though the damage done last century by chlorofluorocarbons and other nasties is expected to heal in the next several decades, the ozone layer over the Southern Hemisphere will remain thinner than its pristine state circa 1965.
The worst effects will come at latitudes above 60 degrees south – the Antarctic Circle plus an extra sliver – during October, November and December. That region and season will also see the most year-to-year variability: by 2095, the UVI will be about 10% higher than 1965 on average, but up to 20% higher in some years. In comparison, the maximum values caused by the ozone hole were about a 50% jump from 1965.
The elevated UV levels could pose a health hazard for Antipodeans, say the authors, and could also affect crops and phytoplankton. Sounds like a climate feedback waiting to be modelled.