Carbon offsetting is the practise of mitigating the carbon produced either by specific actions, such as flying or by drivng your car or for your whole lifestyle.
You would 'offset' the carbon produced by your actions, perhaps by planting enough trees to absorb the carbon produced or by making a donation to protect trees from being cut down, or to an organisation to carring out environmental work in reducing carbon emissions.
Although tree planting was originally the most common way of carbon offsetting, investment in renewable energy, energy conservation and methane capture projects are now become increasingly popular.
There has been much critism of the whole concept of carbon offsetting, for example by Friends of the Earth and journalist George Monbiot. The main critism is that it is much more urgent that we reduce the amount of carbon that we produce, rather than assuaging out guilt by spending money on carbon offsets whilst still flying long distances for our holidays. The spoof website Cheat Neutral was created to demonstrate the fundamental fallacy of carbon offsetting.
Others argue that carbon offsetting is useful as long as people do not use it as an excuse to increase carbon producing behavior.
There are a number of carbon offsetting organisations in the UK.