"We know that aerosols in the atmosphere generally cool the Northern Hemisphere by scattering incoming sunlight. This, in turn, increases the movement of heat from the Southern Hemisphere oceans to the Northern Hemisphere oceans via a global oceanic conveyor belt, travelling south from the subtropical Indian Ocean, passing the southern tip of Africa into the south Atlantic and then north along the Gulf Stream" said co-author Dr Wenju Cai.
"Together with a greenhouse gas-induced southward shift the Indian subtropical ocean gyres towards the Antarctic, these processes delay the Indian Ocean warming in the models," Dr Cai said.
"What makes this work fascinating is the fact that human-emitted aerosols have such a large impact on remote ocean temperatures" says Mr Cowan. "For many years aerosols have masked the direct surface warming induced by greenhouse gases in many Northern Hemisphere regions, however in the Southern subtropical Indian Ocean both aerosols and greenhouse gases have historically conspired to produce a net oceanic cooling, and now the reverse of some of these processes is occurring."
Mr Cowan said that despite the observed rapid ocean warming, quantifying exactly how much is due to declining aerosols or increasing greenhouse gases remains difficult, but as human-generated air pollution is all-together phased out, this will undoubtedly reveal the full impact of greenhouse gases.
|Contact: Craig Macaulay|