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.
Thus vertical air motions act to heat the lower atmosphere and cool the higher. The combined effect of those, as a few people mentioned, is that temperature on the average decreases with altitude in the troposphere-at a rate of 6.5 Â°C per km (3.6 Â°F per 1000 ft.). Yet the lapse rate varies depending on conditions.