What are the troposphere, stratosphere and mesosphere?
The atmosphere extends a few hundred kilometres above the Earth. It is made of layers that surround the Earth like rings. However, 99% of its total mass lies in two regions within the first 50 kilometres above the Earth s surface. These two regions are called the troposphere and the stratosphere. Both are of particular importance in understanding the climate system. The troposphere is closest to the Earth. It extends to about 6 to 17 kilometres above the Earth s surface and is thickest at the equator. Temperatures in the troposphere are warmer nearest the Earth, in part because gases in the troposphere are warmed by heat radiated from the Earth. The stratosphere extends out, beyond the troposphere, to about 50 kilometres above the Earth. Gases in the stratosphere are heated mainly by incoming radiation from the sun. Temperatures in the stratosphere get gradually warmer as altitude increases. The exchange of air between these two layers is slow because of the temperature differences and
