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

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

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