The Cooling
The cooling is accomplished by radiation from the Earth.
The upper line on this graph is a calculation of the radiation from a hypothetical black body that is heated to 294 degrees Kelvin which is an average temperature of the world of 21 degrees C. The area underneath the upper line is the outgoing long wave radiation if there are no Green House gases.
The area colored in blue is typical of an actual measurement. It is the radiation measured by an instrument located at the top of the Earth’s atmosphere. (This data has been collected by NASA)
There are indentations of this that coincide with the frequency of radiation that is absorbed by Water (H20), Carbon Dioxide (CO2), Ozone (O3) and at the higher frequencies, Methane (CH4) and then more water. These gases, including water, are commonly referred to as the Greenhouse Gases.
The important function of the Greenhouse gases is that they absorb some of the energy radiated by the earth and then they radiate it out, some to space and some back to earth. The net effect is that some of the energy that they radiate out is re absorbed by the earth and there is a continuous interchange of energy between these gases and the Earth. With respect to CO2 and Methane this is a small effect but over long periods of time that heating effect by greenhouse gases causes the average temperature of the Earth to increase.
In the early 1900’s the average temperature was 15 degrees C.
Today it is about 1.3 degrees higher than that.