Did Asia air pollution reduce global warming?
Smoke belching from Asia's rapidly growing economies is largely responsible for a halt in global warming in the decade after 1998 because of sulphur's cooling effect, even though greenhouse gas emissions soared, a U.S. study said on Monday.
The paper raised the prospect of more rapid, pent-up climate change when emerging economies eventually crack down on pollution.
World temperatures did not rise from 1998 to 2008, while man-made emissions of carbon dioxide from burning fossil fuel grew by nearly a third, various data show.
The researchers from Boston and Harvard Universities and Finland's University of Turku said pollution, and specifically sulphur emissions, from coal-fueled growth in Asia was responsible for the cooling effect.
Sulphur allows water drops or aerosols to form, creating hazy clouds which reflect sunlight back into space.
"Anthropogenic activities that warm and cool the planet largely cancel after 1998, which allows natural variables to play a more significant role," the paper said.
Natural cooling effects included a declining solar cycle after 2002, meaning the sun's output fell.
The study said that the halt in warming had fueled doubts about anthropogenic climate change, where scientists say man-made greenhouse gas emissions are heating the Earth.
"It has been unclear why global surface temperatures did not rise between 1998 and 2008," said the study published in the Proceedings of the National Academy of Sciences of the United States.