General Article Climate and climate change: some background science

Topic Selected: Climate Change
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The greenhouse effect

The Sun is the primary source of energy for the Earth’s climate. Satellite observations show that about 30% of the Sun’s energy that reaches the Earth is reflected back to space by clouds, gases and small particles in the atmosphere, and by the Earth’s surface. The remainder, about 240 Watts per square metre (W/m2) when averaged over the planet, is absorbed by the atmosphere and the surface.

To balance the absorption of 240 W/m2 from the Sun, the Earth’s surface and atmosphere must emit the same amount of energy into space; they do so as infrared radiation. On average the surface emits significantly more than 240 W/m2, but the net effect of absorption and emission of infrared radiation by atmospheric gases and clouds is to reduce the amount reaching space until it approximately balances the incoming energy from the Sun. The surface is thus kept warmer than it otherwise would be because, in addition to the energy it receives from the Sun, it also receives infr...

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