In a statement released by his spokesman, the Secretary-General said the new study and expected follow-up IPCC reports “will be critical guides for the UN’s response to anthropogenic climate change,” and will support action by those concerned globally, nationally and locally.

The IPCC, which brings together the world’s leading climate scientists and experts, concluded that major advances in climate modelling and the collection and analysis of data now give scientists “very high confidence” – at least a 9 out of 10 chance of being correct – in their understanding of how human activities are causing the world to warm. This level of confidence is much greater than the IPCC indicated in their last report in 2001.

Today’s report, the first of four volumes to be released this year by the IPCC, also confirms that it is “very likely” that humanity’s emissions of carbon dioxide, methane, nitrous oxide and other greenhouse gases have caused most of the global temperature rise observed since the mid-20th century. The report says that it is likely that effect of human activity since 1750 is five times greater than the effect of fluctuations in the sun’s output.

Susan Soloman, co-chair of the IPCC working group that produced the report, said records from ice cores, going back 10,000 years, show a dramatic rise in greenhouse gases from the onset of the industrial era. “There can be no question that the increase in these greenhouse gases are dominated by human activity.”

Three years in the making, the report is based on a thorough review of the most-up-to-date, peer-reviewed scientific literature available worldwide. IPCC Chair Rajendra Pachuari said the science has “moved on” and the extent of knowledge and the research carried is now several steps beyond what was possible for the last report.

The report describes an accelerating transition to a warmer world – an increase of 3°C is expected this century – marked by more extreme temperatures including heat waves, new wind patterns, worsening drought in some regions, heavier precipitation in others, melting glaciers and Arctic ice, and rising global average sea levels.

“This report by the IPCC represents the most rigorous and comprehensive assessment possible of the current state of climate science and has considerably narrowed the uncertainties of the 2001 report,” said Michel Jarraud, Secretary General of the World Meteorological Organization (WMO).

“The 2nd of February, 2007 in Paris will perhaps one day be remembered as the day where the question mark was removed behind the debate on whether climate change has anything to do with human activity on this planet,” said Achim Steiner, Executive Director of the United Nations Environment Programme (UNEP).

“Momentum for action is building; this new report should spur policymakers to get off the fence and put strong and effective policies in place to tackle greenhouse gas emissions,” he said.

The report also concludes that:

• The world’s average surface temperature has increased by around 0.74°C over the past 100 years (1906 - 2005). A warming of about 0.2°C is projected for each of the next two decades.
• The best estimates for sea-level rise due to ocean expansion and glacier melt by the end of the century (compared to 1989 – 1999 levels) have narrowed to 28 - 58 cm, versus 9 - 88 cm in the 2001 report, due to improved understanding. However, larger values of up to 1 m by 2100 cannot be ruled out if ice sheets continue to melt as temperature rises.
• Sea ice is projected to shrink in both the Arctic and Antarctic regions. Large areas of the Arctic Ocean could lose year-round ice cover by the end of the 21st century if human emissions reach the higher end of current estimates. The extent of Arctic sea ice has already shrunk by about 2.7 per cent per decade since 1978, with the summer minimum declining by about 7.1 per cent per decade.
• Snow cover has decreased in most regions, especially in spring. The maximum extent of frozen ground in the winter/spring season decreased by about 7 per cent in the Northern Hemisphere over the latter half of the 20th century. The average freezing date for rivers and lakes in the Northern Hemisphere over the past 150 years has arrived later by some 5.8 days per century, while the average break-up date has arrived earlier by 6.5 days per century.
• It is “very likely” that precipitation will increase at high latitudes and “likely” it will decrease over most subtropical land regions. The pattern of these changes is similar to what has been observed during the 20th century.
• It is “very likely” that the upward trend in hot extremes and heat waves will continue. The duration and intensity of drought has increased over wider areas since the 1970s, particularly in the tropics and subtropics. The Sahel, the Mediterranean, southern Africa and parts of southern Asia have already become drier during the 20th century.
• The number of tropical cyclones (typhoons and hurricanes) per year is projected to decline. However, the intensity of these storms is expected to increase, with higher peak wind speeds and more intense precipitation, due to warmer ocean waters.