IPCC 11/17/2007 REPORT EXCERPT

LINK to the summary report, PDF version.

Most of the observed increase in globally-averaged temperatures since the mid-20th century is very likely due to the observed increase in anthropogenic GHG concentrations.7 It is likely there has been significantanthropogenic warming over the past 50 years averaged over each continent (except Antarctica) (FigureSPM.4). {2.4}

During the past 50 years, the sum of solar and volcanic forcings would likely have produced cooling. Observed patterns of warming and their changes are simulated only by models that include anthropogenic forcings.

IPCC defines "very likely" here:

In this Summary for Policymakers, the following terms have been used to
indicate the assessed likelihood, using expert judgement, of an outcome or
a result: Virtually certain > 99% probability of occurrence, Extremely likely >
95%, Very likely > 90%, Likely > 66%, More likely than not > 50%, Unlikely
< 33%, Very unlikely < 10%, Extremely unlikely < 5%