Scientists can now say with extreme confidence that human activity is the dominant cause of the global warming observed since the 1950s, a new report by an international scientific group said Friday.
Calling man-made warming "extremely likely,'' the Intergovernmental Panel on Climate Change used the strongest words yet on the issue as it adopted its assessment on the state of the climate system.
In its previous assessment, in 2007, the U.N.-sponsored panel said it was "very likely'' that global warming was man-made.
It now says the evidence has grown thanks to more and better observations, a clearer understanding of the climate system and improved models to analyze the impact of rising temperatures.
"Our assessment of the science finds that the atmosphere and ocean have warmed, the amount of snow and ice has diminished, the global mean sea level has risen and the concentrations of greenhouse gases have increased,'' said Qin Dahe, co-chair of the working group that wrote the report.
The full 2,000-page report isn't going to be released until Monday, but a summary for policymakers with the key findings was published Friday. It contained few surprises as many of the findings had been leaked in advance.
As expected, the IPCC raised its projections of the rise in sea levels to 10-32 inches (26-82 centimeters) by the end of the century. The previous report predicted a rise of 7-23 inches (18-59 centimeters).
The IPCC assessments are important because they form the scientific basis of U.N. negotiations on a new climate deal. Governments are supposed to finish that agreement in 2015, but it's unclear whether they will commit to the emissions cuts that scientists say will be necessary to keep the temperature below a limit at which the worst effects of climate change can be avoided.
Using four scenarios with different emissions controls, the report projected that global average temperatures would rise by 0.3 to 4.8 degrees C by the end of the century. That's 0.5-8.6 F.