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Most of us learn at school that warm air rises and cool air sinks. This has always appeared to be fundamental principle of science. However, study from University of California, Davis found that there are circumstances in which cool air rises. Researchers discovered that in tropical atmospheres, cold air rises because of lightness of water vapour. Apparently, in warmer and more humid climates, water particles become more buoyant and can help cooler air rise. Lead researcher Dr Da Yang said: "Water vapour has buoyancy effect which helps release heat of atmosphere to space and reduce degree of warming. Without this lightness of water vapour, climate warming would be even worse."

scientists said humid air is lighter than dry air at same temperatures and pressure. This is called vapour buoyancy effect. It allows cooler air containing water droplets to rise, which then forms clouds and thunderstorms. The resulting rain has cooling effect in tropical areas. Another researcher, Seth Seidel, said more research is needed to find out effects rising cool air has on climate change, and on its impact on curbing effects of global warming. Seth Seidel said: "Now that we understand how lightness of water regulates tropical climate, we plan to study whether global climate models accurately represent this effect." The study is published in journal "Science Advances".

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