A new report by an international scientific group has listed human activity as the most likely reason behind global warming observed since the 1950s.

The report by the UN-sponsored Intergovernmental Panel on Climate Change (IPCC) used the strongest words yet on the issue, saying man-made warming was "extremely likely".

The full 2,000-page report will not be released until Monday, but a summary with key findings was published at a meeting of the IPCC in Stockholm, Sweden, on Friday.

In its previous assessment, in 2007, the panel had 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 analyse the impact of rising temperatures.

The report says sea levels are set to rise 26-82 centimeters
by end of century [EPA]

"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.

As expected, the IPCC raised its projections of the rise in sea levels to 26-82 centimetres by the end of the century. The previous report predicted a rise of 18-59 centimetres.

The IPCC assessments are important because they form the scientific basis of UN 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.

"There are few surprises in this report but the increase in the confidence around many observations just validates what we are seeing happening around us," said Samantha Smith, of the World Wildlife Fund.

One of the most controversial subjects in the report was how to deal with a purported slowdown in warming in the past 15 years. Climate sceptics say this "hiatus" casts doubt on the scientific consensus on climate change. In the summary of the new report, the IPCC stressed that short-term records are sensitive to natural variability and do not in general reflect long-term trends.

Source: Al Jazeera and agencies