# What happens to the energy from the sunlight?

On average, about 342 watts are received per square meter of the Earth's surface in the constant radiation of the sun. But thanks to the surface's good ability to reflect…

On average, about 342 watts are received per square meter of the Earth’s surface in the constant radiation of the sun. But thanks to the surface’s good ability to reflect light, the planet doesn’t get hotter all the time.

The sunlight does not disappear when it reaches the earth, but is partly reflected and partly absorbed by the earth.

This is described by the first law of thermodynamics, which states that the energy in the electromagnetic radiation that forms sunlight is conserved.

The surface has the ability to reflect part of the sunlight. This is called reflectivity, and the reflected light we see as colors.

If a certain surface reflects all visible light, we see that surface as white.

The reflectivity of the surface is then considered to be close to 1. If a surface does not reflect any light, we see it as black and the reflectivity is then 0.

#### The Earth gives off as much energy as it receives

The Earth’s atmosphere, clouds and the surface itself reflect about 30% of the sunlight, and the reflectivity of the globe is thus about 0.30.

The top soil layer absorbs the other 70% of the sunlight and the energy raises the temperature.

This heat is then given off by the earth, either in the form of long-wave thermal radiation, or through the evaporation of water.

The earth needs to give off as much thermal energy as it receives in order to maintain its stability.

A planet’s ability to reflect sunlight is called reflectivity. The Earth’s reflectivity is 0.30, which means that 30% of sunlight is reflected back into space. This number is an average of the reflectivity of the vaporosphere, clouds and the Earth’s surface.