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Aerosols affect rainfall variability more than greenhouse gases
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Submitted by astone on Tue, 10/23/2012 - 11:26
New research published in Geophysical Research Letters on global variations in precipitation indicates aerosols may have affected global rainfall variability far more than greenhouse gases over the past 60 years The research led by researchers from the ARC Centre of Excellence for Climate System Science (CoECSS) also showed that, on average, wet areas were getting drier and dry areas were getting wetter, in contrast to a widely held tenet that dry areas would get drier and wet areas get wetter under climate change. “If, as many climate researchers suspected, wet areas were becoming wetter and dry areas were getting drier, we should have seen an increase in the variation of precipitation when compared across these wet and dry regions,” said one of the paper’s authors and CoECSS chief investigator Dr Michael Roderick. “Instead we found the differences in precipitation between these regions declined, with, on average, wet areas getting drier and drier areas getting wetter.” The research also showed that at a globally averaged level there was a near zero-trend in total precipitation worldwide with increased precipitation in one region balanced by decreases in another region. However, at a regional level, it was found there was a strong correspondence between those areas where variability in precipitation had changed significantly and those with heightened aerosol emissions, such as China and India. “This correspondence between aerosols and variation in precipitation adds another layer of complexity around how precipitation may be altered under climate change,” Dr Roderick said. “These results suggest intensive investigation will be required to separate the impacts of greenhouse gases, natural variability and aerosols on precipitation variability.” The authors reached their conclusions using an elegant new method. The development of this new method was led by CoECSS Research Fellow Dr Fubao Sun. The method initially lumps together worldwide observations in precipitation over land between 1940-2009 to create a total global figure for these variations called the grand variance. The authors then separated the global landmass into almost 2000 grid boxes where there had been reliable observations for 50 years or more. Using these regional observations they were able to calculate the changes in variability of precipitation over time for each box. This approach enabled them to detect changes in precipitation variability across multiple regions, revealing how shifts in one area were balanced by precipitation shifts in another. “For the first time we could disentangle the time and spatial components of precipitation to reveal how changes in precipitation cascaded from one area to another,” said Dr Roderick. “It has allowed us to test assumptions and shows that there is still more research required to understand the effects of climate change on precipitation.”
View the paper
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