In the light of new evidence and taking into account the remaining uncertainties, most of the observed warming over the last 50 years is likely to have been due to the increase in greenhouse gas concentrations.There are three important caveats in this statement, which are often ignored by strawman-toting advocates.
- "most of the observed warming": this says that humans contributed > 50% of the warming, but it leaves the door open for a significant amount to be due to non-human influences.
- "last 50 years": this says that we can identify the hand of humans in only the recent warming; before that, the data are too poor to unambiguously assign the cause of the warming.
- "likely": in the carefully nuanced language of the IPCC, "likely" denotes a confidence of about 75%. Thus, there is a possibility that this statement is wrong. This reflects the fact that our knowledge of the climate is imperfect, and it is possible though unlikely that new research could significantly revise our understanding of the climate system.