Natural England - What are the causes of climate change?
What are the causes of climate change?
Climate change is caused by changes in the heat stored in the earth’s atmosphere. In the past, such changes have been caused by factors such as major volcanic eruptions, which have reduced the amount of sunlight hitting the earth, or natural changes in the sun’s activity.
The global greenhouse
When sunlight hits the earth:
- some is scattered back into space by the atmosphere
- some is reflected back from the earth’s surface
- some is radiated from the warmed surface
- most is absorbed by the so-called 'greenhouse gases':
- water vapour
- carbon dioxide
- methane
- nitrous oxide
- Halocarbons (including CFCs or chlorofluorocarbons – also responsible for the ozone holes above the earth’s poles).
The 'greenhouse effect' of the atmosphere is vital in maintaining the average global temperature at about 15ºC instead of the -6ºC that we would be without it.Nowadays, we are worried about changes in the gases that make up the atmosphere, which human activities are causing. These changes are making the atmosphere store more heat than it used to, and so the globe is warming.
Greenhouse gases
Many human activities, since the industrial revolution began in the 1750s, have increased the atmospheric concentrations of some of the key greenhouse gases.
The most important change has been a 37 per cent increase in carbon dioxide since 1850. This has been responsible for 70 per cent of the global warming to date. Carbon dioxide is released by the burning of fossil fuels, eg coal, oil, gas, the burning and clearance of forests and the draining and degradation of peatlands.
The next most important change in a greenhouse gas has been in methane, which has doubled in concentration since the 1800s due to leaks from gas fields, decomposition of vegetation in rice paddies, emissions from livestock, and the decay of rubbish in landfill sites. Methane is responsible for 24 per cent of global warming so far.
The third most important change is in nitrous oxide, which is generated from industrial processes, deforestation and agriculture. This has increased in concentration by 13 per cent since pre-industrial times and is responsible for about 6 per cent of global warming so far.