http://en.wikipedia.org/wiki/Attributio ... ate_change
Attribution of recent climate changeIn short attribution means they have a very high level of confidence that what they are saying is true.
increasing atmospheric concentrations of greenhouse gases
global changes to land surface, such as deforestation
increasing atmospheric concentrations of aerosols.
There are also natural mechanisms for variation including climate oscillations, changes in solar activity, variations in the Earth's orbit, and volcanic activity.
Attribution of recent change to anthropogenic forcing is based on the following facts:
The observed change is not consistent with natural variability.
Known natural forcings would, if anything, be negative over this period.
Known anthropogenic forcings are consistent with the observed response.
The pattern of the observed change is consistent with the anthropogenic forcing.
Recent reports from the Intergovernmental Panel on Climate Change (IPCC) have concluded that:
"Most of the observed increase in globally averaged temperatures since the mid-20th century is very likely due to the observed increase in anthropogenic greenhouse gas concentrations"; It is extremely unlikely (<5%) that the global pattern of warming during the past half century can be explained without external forcing (i.e., it is inconsistent with being the result of internal variability), and very unlikely that it is due to known natural external causes alone. The warming occurred in both the ocean and the atmosphere and took place at a time when natural external forcing factors would likely have produced cooling.
"From new estimates of the combined anthropogenic forcing due to greenhouse gases, aerosols, and land surface changes, it is extremely likely that human activities have exerted a substantial net warming influence on climate since 1750."
"It is virtually certain that anthropogenic aerosols produce a net negative radiative forcing (cooling influence) with a greater magnitude in the Northern Hemisphere than in the Southern Hemisphere.
The panel defines "very likely," "extremely likely," and "virtually certain" as indicating probabilities greater than 90%, 95%, and 99%, respectively. The IPCC's attribution of recent global warming to human activities is a view shared by most scientists,:2 and is also supported by a number of scientific organizations (see scientific opinion on climate change).