Friday’s report from the United Nations Intergovernmental Panel on Climate Change (IPCC) has reached specific conclusions on global warming, including the following:
- The world’s average surface temperature has increased by around 0.74°C over the last 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 panel’s 2001 report, due to improved understanding). But 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 decade since 1978, with the summer minimum declining by about 7.1% 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% 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 breakup 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.
Yvo de Boer, executive secretary of the UN Framework Convention on Climate Change, has called for speedy and decisive international action to combat the average temperature rise of around 3°C this century.
“The findings, which governments have agreed upon, leave no doubt as to the dangers mankind is facing and must be acted upon without delay,” he says. “Any notion that we do not know enough to move decisively against climate change has been clearly dispelled. It is politically significant that all the governments have agreed to the conclusions of the scientists, making this assessment a solid foundation for sound decision-making.
“The world urgently needs new international agreement on stronger emission caps for industrialized countries, incentives for developing countries to limit their emissions and support for robust adaptation measures,” he adds. “The good news is that the worst predictions of the IPCC are based on scenarios which do not take into account action to combat climate change now or in the future. Both the policies and technologies to prevent such consequences are available, and putting them in place is precisely what the Climate Convention and the Kyoto Protocol are designed to do.”
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