Atmospheric carbon dioxide is the primary source of carbon in life on Earth and its concentration in Earth's pre-industrial atmosphere since late in the Precambrian was regulated by photosynthetic organisms and geological phenomena.
At about 55 km, the mesosphere begins. In the mesosphere, the temperature decreases with height again, because there is very little ozone to warm up the air. Finally, the mesopause divides the mesosphere from the thermosphere, which is the section of the atmosphere higher than 90 km. In this region, the temperature increases again. This time, it is molecular oxygen (O2) that causes the temperature increase.
The net effect of clouds on the climate today is to cool the surface by about 5Â°C (9Â°F). One can calculate that a higher surface temperature would result from the buildup of greenhouse gases in the atmosphere and the consequent slowing of heat radiation from the surface, provided nothing else changes.