The amount of deep convective clouds in the north Pacific increased by between 20 percent and 50 percent between 1994 and 2005 compared to the previous decade, according to satellite data analysed by the climatologists.

The trend reflected the pattern followed by the Pacific storm track, a major weather event during the northern hemisphere during winter.

The researchers say the trend appears to be unrelated to other climatic conditions, such as changing sea temperatures or the El Nino weather system, but computer modeling suggests it is entirely consistent with the worsening atmospheric pollution over Asia.

The rapid urbanization and industrialization of parts of the region, and in particular China and India, have led to dramatic increases in concentrations of atmospheric aerosols, according to long-term satellite data.

Aerosols are particles of sulfur and soot that are expelled during the burning of fossil fuels.

Previous research has shown that atmospheric aerosols can influence the formation and precipitation of clouds, although the extent to which this happened was unclear.

In addition, the prevailing winds carry the pollution from Asia to the north Pacific, which is particularly susceptible to the aerosol effect during winter months because of various climate conditions.

"This pollution directly affects our weather," said Renyi Zhang, professor of atmospheric sciences at Texas A&M University and lead author of the paper.

"The Pacific storm track plays a crucial role in our weather, and there is no doubt at all that human activity is changing the world's weather."

The study is the first work to provide indisputable evidence that man-made pollution is adversely affecting the storm track over the Pacific Ocean said Zhang, who suggested that the repercussions might not stop there.

The Pacific storm track carries the polluted particles to the West Coasts of Canada, and the United States and across America, and eventually to most of the rest of the world.

If some of that pollution ended up on the polar ice caps, the results could be catastrophic, he warned. In particular, if soot in the form of black carbon collected on ice packs and attracted heat from the sun, it could accelerate the melting of the polar ice caps, and push sea levels higher.

"The Pacific storm track can impact weather all over the globe," he said.

The paper appears in the Proceedings of the National Academy of Sciences and was co-authored by researchers at NASA's Jet Propulsion Laboratory in Pasadena, the Massachusetts Institute of Technology and the University of California, San Diego.

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