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.