Global observations

The rate of change

The earth's weather systems have gone through change over hundreds of thousands of years, but it is the current rate of temperature increases and changes that are now happening in weather patterns which currently have scientists across the world agreeing that the following changes are happening right now:¹

• average air temperatures are rising
• average ocean temperatures are rising
• there is widespread melting of snow and ice
• average sea levels are rising.

The reasons for the changes

Changes in the balance of energy in the climate system are caused by:

• changing concentrations of gases in the atmosphere;
• the presence of aerosols in the atmosphere;
• changes in the land cover (e.g. vegetation being removed for housing developments)
• variations in solar energy emitted from the sun.

These variables can affect the absorption, scattering and emission of radiation, or heat, within the atmosphere and the earth's surface. Sample measurements taken from the ice and from the atmosphere can demonstrate the concentrations of gases in the earth's atmosphere over the last 10 000 years.

Find out more about past ice ages and sea level changes.

The diagram on the right shows the atmospheric concentrations of carbon dioxide, methane and nitrous oxide over the last 10 000 years (largest boxes). A dramatic increase in emissions since 1750 can be seen (inset boxes) and this is what scientists believe is making the biggest contribution to observed climate changes. These measurements come from ice cores (symbols of different colours indicate different studies) and samples taken from the atmosphere (red lines). The corresponding radiative forcings (relative to 1750) are shown on the right-hand axes of the large panels, and allow each gas to be compared against the others for its warming potential, or how well that gas traps heat in the atmosphere.

Diagram: 'Climate change 2007: Synthesis report', Intergovernmental Panel on Climate Change (IPCC).

Return to What is climate change?.

¹Intergovernmental Panel on Climate Change (IPCC), Climate Change 2007: Synthesis report, 'An assessment of the Intergovernmental Panel on Climate Change', A Allali, R Bojariu, S Diaz, I Elgizouli, D Griggs, D Hawkins, O Hohmeyer, B Pateh Jallow, L Kajfez-Bogataj, N Leary, H Lee & D Wratt (eds), Cambridge University Press, Cambridge, 2007.
http://www.ipcc.ch/publications_and_data/publications_ipcc_fourth_assessment_report_synthesis_report.htm