We can collect evidence to show that our climate is changing. This is due to a combination of natural factors and human influence, and the effects are multiple.
How our climate has changed
Our climate is continually changing. There is evidence for this change, for example from fossils, which tell us that at certain times the world has been much warmer than it is now, and there was little ice on the North Pole. There is also evidence to suggest that at other times the ice cover was much greater than it is today.
Evidence is collected by:
- Weather recordings – thermometers are more accurate now and digital readings can be recorded remotely.
- Ice cores – locked inside ice are molecules and trapped air, which are preserved year on year with more snowfall. Subtle changes in temperature can be measured from ice cores extracted in Antarctica.
- Rocks and fossils – these can be studied for information covering longer time periods. For instance, limestone found in Yorkshire would have been formed on the bottom of a warm seabed millions of years ago.
- Analysis of pollen and trees.
Other observations confirm evidence that the climate is changing:
- Ice cover – areas such as Greenland and the Arctic have seen thinning of ice sheets.
- Glacial retreat – photos show that many mountain glaciers have retreated in the last 50 years. However this could partly be due to a lack of snowfall.
Since about 1950 there is evidence of a steep climb in global temperature compared to the past. This trend is called global warming.
For the last 10,000 years our climate has averaged about 14°C globally. However in the last 100 years, as the graph above shows, our climate has started to change rapidly.
- Increases in temperatures have been recorded on land and in the oceans.
- Changes to the rainfall pattern have been observed – these are sometimes more extreme (which means that locations are either a lot wetter or a lot drier than they used to be). At other times the rainfall pattern is out of season. The extreme rainfall in the UK during the summer of 2007 is an example of this. However, in general, UK summers are getting drier and winters are getting wetter.
- The lengths of seasons are changing – the UK growing season is lengthening.
Why our climate has changed
There are natural changes in our climate. These are caused by:
- variations in the energy from the sun
- the way the earth orbits the sun
- the way oceans transfer heat from one area to another
- volcanic activity (dust particles released in an eruption can disrupt the atmosphere)
Humans also cause changes to our climate. The biggest contributor is gas released into the atmosphere from cars and burning fossil fuels. MEDCs contribute the most in carbon dioxide. Other gases such as methane (produced from cow dung, decaying landfill and peat bogs) also contribute to climate change.
Effects of climate change
- Crop yields are expected to decrease for all major world crops.
- Agricultural land on the edge of deserts becomes unusable, through the process of desertification.
- Crops could be wiped out in low-lying areas that suffer from flooding. With less crops available on the world market, prices are likely to increase.
- The growing season in some areas will increase. This is a benefit to places such as the UK as more crops could be grown.
Sea level changes
- Coastal land is at risk, especially land on deltas.
- Sea defences are under more stress.
- Low-lying land is threatened so the lives of 80 million people across the globe are threatened.
Water and ice
- More mass movement can occur as glaciers melt.
- Communities that use the melt water from glaciers may see this supply decrease. This is especially the case in Asia.
- Economies that rely on skiing as a form of income may suffer as the skiing season is reduced or disappears through lack of snow.
- Locations suffering from water stress will increase in number.
- Less fresh water will be available in coastal areas as it will mix with sea water, which is salty.
- People will migrate from areas suffering drought. Any that remain will be in danger of dying from starvation and lack of water.
- 17 million people in Bangladesh alone will be threatened by flooding.
- As the world population increases, more people will be living in cities located on the coast. More people will be affected by coastal flooding as a result.
Areas at risk from climate change