What is climate change?

"Climate change refers to a statistically significant variation in either the mean state of the climate or in its variability, persisting for an extended period (typically decades or longer). Climate change may be due to natural internal processes or external forcing, or to persistent anthropogenic changes in the composition of the atmosphere or in land use." (IPCC)

There is ample evidence that significant climate change is currently happening, e.g. global mean temperatures rose by more than 0.7°C during the 20th century, and that its causes are mainly anthropogenic. Furthermore, the IPCC scenarios suggest an increase in global mean temperature of between 1.4 and 5.8ºC by the end of the 21st century, depending strongly on the development of the main anthropogenic driving factor, namely greenhouse gas emissions due to fossil fuel combustion, industrial processes and land use and cover changes.