Solar Radiation

Solar Radiation

About 30% of solar radiation is reflected space and the rest is absorbed by oceans, clouds, and landmasses.

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Essentially 100% of the energy that fuels the earth comes from the sun. To maintain a constant global average temperature, all of the sun's radiation that enters Earth's atmosphere must eventually be sent back to space. This is achieved through Earth's energy balance. Figure A depicts how the energy from the sun is absorbed, reflected, and emitted by the earth.

100% of the energy entering the earth's atmosphere comes from the sun.

50% of the incoming energy is absorbed by the earth's surface i.e. the land and oceans.

30% is directly reflected space by clouds, the earth's surface, and different gases and particles in the atmosphere (the earth's albedo is 0.3 on average).

20% is absorbed by the atmosphere and clouds.

70% of the sun's energy that is absorbed by the earth's surface, clouds, and atmosphere causes warming. Any object or gas that has a temperature emits radiation outward, and this is ultimately re-radiated back into space. This occurs 24 hours a day, and the energy is emitted as longwave radiation due to the characteristic temperatures of the earth and atmosphere.

Consider a stove, for example. If you were cooking, you'd have the burner turned on so it would heat up. The burner is like the earth and the heat source, be it gas or electric, is like the sun. When you're done cooking you turn off the burner, but it stays hot for a long while even after the heat source is gone. Turning off the burner is like the sun going down. Even though there is no more energy input, there is still energy output in the form of infrared radiation. The burner stays hot because it's still emitting the energy it absorbed earlier, just like the earth. This time delay is sometimes called "thermal inertia."

Most of the energy emitted from the earth's surface does not go directly out to space. This emitted energy is reabsorbed by clouds and by the gases in the atmosphere. Some of it gets redistributed by convection. Even more, energy is released into the atmosphere through condensation. The majority of the energy is reabsorbed by greenhouse gases such as methane, nitrous oxide, ozone, carbon dioxide, and water vapor. These gases constantly emit the sun's energy back into the atmosphere and keep the earth at a habitable temperature. About 30% of solar radiation is reflected in space and the rest is absorbed by oceans, clouds, and landmasses.


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