The Sun’s energy powers our planet's climate but not all the energy that reaches the top of the atmosphere makes it to the Earth’s surface. Some of the energy can be reflected or absorbed by aerosols floating in our atmosphere. Aerosols come from natural sources including volcano eruptions that emit ash, sulfates, and other gases; or from sandstorms that pick up mineral dust from deserts; or winds that pick up sea salts from oceans; and forest fires that produce black and organic carbon particles. But aerosols can also come from human activities. For example, fertilizers used in farming produce nitrate particles; coal power plants create sulfates and other aerosols; and cars emit black and organic carbon. Most aerosols (like pure sulfates, salt, and nitrates) are bright colored or translucent particles. Having a bright surface means they are reflective, so they are able to reflect radiation to outer space, and can therefore cool the planet. Which is what happened after the Mount Pinatubo volcano eruption in 1991. It ejected 20 million tons of sulfur dioxide into the atmosphere, high above the clouds, where the particles didn't get washed away by rain. And as a result, the global temperatures dropped by half a degree for two years. But darker aerosols (like black carbon from fossil fuel burning) absorb light and warm up the planet. Together, the net impact of both types of aerosols have helped cool the planet and countered the warmer temperatures caused by more greenhouse gases. So, while solar radiation, greenhouse gases & aerosols are the initial drivers in our climate system, there are also processes that can amplify or diminish these influences. One of those processes is clouds. In the next video, we'll give you a quick recap of how clouds are formed, the different types and their effect on the climate.

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