The physical process responsible for climate change is in essence very simple. Greenhouse gases such as CO2 are created on the earth’s surface in a range of ways but most significantly from human activity. Once emitted, these gases "thicken" the atmosphere which in turn reduces the amount of heat generated by the sun that can escape back into space. This results in a warming of the earth's surface or climate change.
While atmoshpheric CO2 levels vary naturally (broadly in sequence with ice ages) analysis of Law Dome and Vostok ice cores in eastern Antarctica show that, since the start of the industrial revolution in the mid 19th century, these have increased dramatically and are now some 30% higher than at any time over the last 400,000 years.
Over the same period average global temperatures have risen by 0.7°C (1.0°C on land), sea levels have risen by 10-20cm, and the rate of change is accelerating. 20 of the 21 hottest years ever recorded have been experienced since 1980.
Without substantive change, the IPCC (Intergovernmental Panel on Climate Change) forecast that average global temperatures will rise by between 1.8°C and 4.0°C by the end of the century, leading to:
In the UK, the Hadley Centre for climate change (part of the Met Office and the UK Government’s representative on the IPCC) have forecast:
Atmospheric CO2 concentrations