The term climate change is used to refer to all forms of significant climatic differences from the 'average weather'. These changes take the form of rising temperatures, change in rain patterns, increased droughts, sea level variations and so on. Climate change may take place on a regional or global level and the time scale can vary over years, decades, centuries or millennia.
Evidence for long term climate change comes from a variety of sources. These include:
- Ice Core Samples - Oxygen isotope Analysis
- Pollen Analysis
- Boreholes and ocean sediment
- Coral growth
- Surveys of River Activities
- Analysis of River Sediments
- Changes in Sea Level Studies
- Fossil Records
- Historical Records e.g. cave art and literature
Ice Core Analysis: Ice cores from glaciers in e.g. Greenland and Antarctica that may contain dust, chemicals, and gases that have been deposited with snow over hundreds of thousands of years. These layers reveal past climate characteristics.
Oxygen Isotope Analysis: The use of stable oxygen isotopes found in the gases in ice cores to extract paleoclimatic information from ice cores This provides a record of ancient water temperature and, therefore, ancient climates.
Pollen Analysis: This is the study of pollen found in places like bogs and is very useful in indicating changes in vegetation over the last 10,000 years
Dendrochronology: This is the study of tree rings and has been used to monitor change over the last 4,000 years.
Causes of Climate Change
(The causes are also known as Drivers or Forcings)
The Earth's climate may be altered because of natural causes, or human activities, known as anthropogenic changes.
The Climate can change for a number of reasons:
- Changes in the Earth's orbit every 100, 000 to 400, 000 years.
- Changes in the tilt of the earth's axis - every 41, 000 years
- Changes in the orientation of the earth's axis - every 21, 000 years
- Continental Drift (For example, the North Atlantic Drift could be deflected by the moving continents.)
- Volcanic Emissions ( Volcanic Dust and Gases block out insolation and increase the Earth's albedo (ability to reflect insolation)
- Sunspot activity - every 11 years
- Human activity (e.g. burning of fossil fuels changes the atmospheric composition, deforestation and agricultural practices such as pastoral farming)
Next: Global Warming Timeline