Ozone hole healing could cause further climate warming
26 January 2010
The hole in the ozone layer is now steadily closing, but its repair could actually increase warming in the southern hemisphere, according to scientists at the University of Leeds.
The Antarctic ozone hole was once regarded as one of the biggest environmental threats, but the discovery of a previously undiscovered feedback shows that it has instead helped to shield this region from carbon-induced warming over the past two decades.
High-speed winds in the area beneath the hole have led to the formation of brighter summertime clouds, which reflect more of the sun's powerful rays.
"These clouds have acted like a mirror to the sun's rays, reflecting the sun's heat away from the surface to the extent that warming from rising carbon emissions has effectively been cancelled out in this region during the summertime," said Professor Ken Carslaw of the University of Leeds, who co-authored the research.
"If, as seems likely, these winds die down, rising CO2 emissions could then cause the warming of the southern hemisphere to accelerate, which would have an impact on future climate predictions," he added.
The key to this newly-discovered feedback is aerosol - tiny reflective particles suspended within the air that are known by experts to have a huge impact on climate.
Greenhouses gases absorb infrared radiation from the Earth and release it back into the atmosphere as heat, causing the planet to warm up over time. Aerosol works against this by reflecting heat from the sun back into space, cooling the planet as it does so.
Beneath the Antarctic ozone hole, high-speed winds whip up large amounts of sea spray, which contains millions of tiny salt particles. This spray then forms droplets and eventually clouds, and the increased spray over the last two decades has made these clouds brighter and more reflective.
As the ozone layer recovers it is believed that this feedback mechanism could decline in effectiveness, or even be reversed, leading to accelerated warming in the southern hemisphere.
"Our research highlights the value of today's state-of-the-art models and long-term datasets that enable such unexpected and complex climate feedbacks to be detected and accounted for in our future predictions," added Professor Carslaw.
The Leeds team made their prediction using a state-of-the-art global model of aerosols and two decades of meteorological data. The research was funded by the Natural Environment Research Council's Surface Ocean-Lower Atmosphere Study (UK SOLAS) and the Academy of Finland Centre of Excellence Programme.
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A copy of the paper: 'Aerosol climate feedback due to decadal increases in southern hemisphere wind speeds' is available on request from the University of Leeds press office. An advance online copy will be published in Geophysical Research Letters on Wednesday 27 January.
1. Ken Carslaw is professor of atmospheric science in the School of Earth & Environment, University of Leeds.
2. The £11m UK SOLAS programme has supported more than 25 research projects and nine fieldwork campaigns to investigate the importance of ocean-atmosphere interactions in the climate system. Professor Ken Carslaw will provide an overview of his work at the programme Finale Event at the Met Office, Exeter on 23 March. UK SOLAS is the main national science contribution to the international Surface Ocean-Lower Atmosphere Study.
Press release: 03/10
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