Summary
The atmosphere is the layer of gases around the Earth: mostly nitrogen (78%) and oxygen (21%). In the lowest layer, the troposphere, clouds, rain and wind form; higher up, in the stratosphere, the ozone layer filters out ultraviolet rays. Weather is the state of the atmosphere at one moment; climate is what is usual in a place over about thirty years.
Some gases, such as carbon dioxide, methane and water vapour, hold back part of the heat the Earth gives off: this is the greenhouse effect, without which the planet would be frozen. By burning coal, oil and gas and cutting down forests we have greatly increased those gases, and the planet is warming faster than ever: sea level is rising and there are more heatwaves and droughts. Curbing it means cutting emissions (mitigation) and preparing for what can no longer be avoided (adaptation).
Key points
- Air is mostly nitrogen (78%) and oxygen (21%).
- Weather happens in the troposphere.
- The ozone layer filters out ultraviolet rays.
- Weather: one moment. Climate: the average over many years.
- The natural greenhouse effect keeps the Earth mild.
- Burning fossil fuels increases CO2 and warms the planet.
- Consequences: rising seas, more heatwaves and droughts.
- Mitigation is cutting emissions; adaptation is preparing for the effects.