BEIJING, July 6 (UPI) -- The cooling effect of sulfur emissions resulting from China's massive rise in coal-fired power stations has served to mask the impact of global warming during the last 10 years, a new study indicates.
While the last decade was the hottest on record, global average surface temperatures have held steady, a detail cited by climate-change skeptics as a reason for denying the existence of man-made global warming.
But the new analysis, published Monday in the Proceedings of the National Academy of Sciences, says this leveling of temperatures can be explained by sulfate particles released into the atmosphere from coal-burning power stations, which has the effect of reflecting sunlight and heat away from the Earth.
The impact of the sulfur emissions, along with the sun entering a less intense part of its 11-year cycle and the peaking of the El Nino climate warming phenomenon, the researchers say, has kept global average surface temperatures artificially low.
Coal consumption in China more than doubled from 2003-07, accounting for 77 percent of the increase in coal use worldwide, the study reports. During that period, it says, global sulfur emissions increased 26 percent.
"The rapid growth of the Chinese economy over the past decade and the amount of coal they used to fuel it has tended to cool the climate, which offset to some extent the warming effect of carbon dioxide emissions," Robert Kaufmann of Boston University, who led the study, was quoted as saying by Britain's The Independent newspaper.
But a change in the sun's 11-year cycle, along with initiatives to refine China's coal boilers that would lower sulfur emissions, could cause global average surface temperatures to rise significantly.
Piers Forster, professor of climate change from the United Kingdom's Leeds University, who led the Intergovernmental Panel on Climate Change chapter that analyzed factors affecting global temperatures, said the new study was "interesting and worthwhile."
"The masking of CO2-induced global warming by short-term sulfur emissions is well known. It's believed that the flattening off of global mean temperatures in the 1950s was due to European and U.S. coal burning, and just such a mechanism could be operating today from Chinese coal," he told BBC News.
Forster warned that any masking of the impact of global warming would be short lived, and the increased CO2 from coal-fired plants would remain in the atmosphere for many decades and "dominate" the long-term warming warning over the next decades.
