What is climate change?
Climate change in a nutshell
Our climate is changing, largely due to the observed increases in human produced greenhouse gases. Greenhouse gases absorb heat from the sun in the atmosphere and reduce the amount of heat escaping into space. This extra heat has been found to be the primary cause of observed changes in the climate system over the 20th century. These changes include increases in global average air and ocean temperature, widespread melting of snow and ice and rising global sea levels. The extra heat in the climate system has other impacts, such as affecting atmospheric and ocean circulation, which influences rainfall and wind patterns.
Another serious impact of increases in the greenhouse gas carbon dioxide is ocean acidification. Around a quarter of human-produced carbon dioxide is absorbed by the oceans. As the carbon dioxide dissolves in sea water it forms a weak carbonic acid, making the ocean more acidic. There are early indications that some marine organisms are already being affected by ocean acidification.
Global warming and climate change
The terms 'global warming' and 'climate change' are often used interchangeably, but there is a difference.
- Global warming is the gradual increase of the Earth’s average surface temperature, due to greenhouse gases in the atmosphere.
- Climate change is a broader term. It refers to long-term changes in climate, including average temperature and rainfall.
Greenhouse gases
Greenhouse gases have always been a natural part of the atmosphere. The chemical properties of greenhouse gases mean that they strongly absorb and re-radiate the sun’s warmth in the atmosphere. This process maintains the Earth’s temperature at 33°C warmer than it would otherwise be, allowing life on Earth to exist.
Water vapour is the most abundant greenhouse gas. Its concentration is highly variable and human activities have little direct impact on its amount in the atmosphere. The main greenhouse gases generated by human activity are carbon dioxide (CO2), methane and nitrous oxide. There are also manufactured gases such as chlorofluorocarbons (CFCs), halocarbons and some of their replacements that make a small contribution to global warming.
Over the last 800,000 years, the amount of carbon dioxide in the atmosphere has varied between approximately 172 and 300 parts per million (ppm). Since industrialisation, carbon dioxide levels have risen sharply to about 386 ppm. Even in these amounts, the extra carbon dioxide is largely responsible for the increase in global temperatures of about 0.7oC.
Greenhouse gases and human activity
Greenhouse gases are produced by human activities, including:
- burning fossil fuels, such as coal, oil or gas
- using energy generated by burning fossil fuels
- some aspects of farming, such as raising cattle and sheep, using fertilisers and growing some crops
- clearing land, including logging
- the breakdown of food and plant wastes and sewerage
- some industrial processes, such as making cement and aluminum.