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.
Nearly 30 years after the benchmark was proffered, about half the distance to a 2-degree temperature increase, or about 0.8 degrees, has already been achieved. Further, enough carbon dioxide, the chief planet warming gas that arises when coal, oil and natural gas are burned, is already in the atmosphere to raise future temperatures by another 0.8 degrees, even if all the pollution stopped immediately.