Kigali — A group of influential scientists from around the world have announced that, contrary to previous climate reports and studies, human activities are accelerating global warming with consequences that could soon take decades or centuries to reverse.
The group, the Intergovernmental Panel on Climate Change (IPCC), made up of hundreds of scientists from 113 countries, said that based on new research over the last six years, it is 90 percent certain that human-generated greenhouse gases account for most of the global rise in temperatures over the past half-century. Governments and scientific organisations across the globe nominate scientists to produce and review the IPCC assessment under the auspices of the United Nations.
In their report Climate Change 2007: The Physical Science Basis released on February 2 in Paris, the scientists predict that global temperatures would rise by between 1.8-4.0 Celsius (3.2-7.2 Fahrenheit) by the end of the century. The sea levels on the other hand will rise between seven and 23 inches. Temperatures rose 0.7 degrees in the 20th Century and the 10 hottest years since records began being collected in the 1850s have been since 1994 to date. The world is about 5 Celsius warmer than during the last Ice Age.
This is the first of four reports IPCC intends to publish this year. The others are slated to give details of environmental threats and ways of combating these climatic changes.
"We can be very confident that the net effect of human activity since 1750 has been one of warming," co-lead author Dr Susan Soloman was quoted by the BBC telling delegates in Paris.
In what other media agencies have called unequivocal language, the report says the world would have to undertake "a really massive reduction in emissions," on the scale of 70 to 80 percent, to avert severe global warming in time to come. The report's strong language, it is hoped, will move countries such as the United States and China and big multinational companies to do more to cut greenhouse gases, released mainly by burning fossil fuels in power plants, factories and cars.
The scientists say in the report that it is "very likely" that hot days, heat waves and heavy rainfall will become more frequent in the years to come, and "likely" that future tropical hurricanes and typhoons will become more intense. The Arctic sea ice will disappear "almost entirely" by the end of the century, they said, and snow cover will contract worldwide.
While the summary did not produce any new observations from its previous report in 2001 which was more speculative and putting the probability of human involvement in global warming at 66 percent, it provides much more definitive conclusions that human activity accounted for the warming recorded over the past 50 years.
Some of the report's most compelling sections focused on future climate changes, because the buildup of carbon dioxide in the atmosphere will exert an effect even if industrialised countries stopped emitting greenhouse gases tomorrow. Gerald Meehl, a senior scientist who helped oversee the chapter on climate projections says in the next two decades alone global temperatures will rise by 0.7 degrees Fahrenheit.
"We're committed to a certain amount of warming," said Meehl, who worked with 16 computer-modeling teams from 11 countries.
"A lot of these changes continue through the 21st century and become more severe as time goes on." Meehl added, however, that a sharp cut in greenhouse gas emissions could still keep catastrophic consequences from occurring:
"The message is; it does make a difference what we do."
For the first time, IPCC scientists also looked at regional climate shifts in detail, concluding that rainfall in the American Southwest will decline as summer temperatures rise, just as rainfall in the Northeast will increase. Linda Mearns, another senior scientist who was also one of the lead authors, said these changes could cause water shortages and affect recreational activities in the Southwest. Developing countries in Africa and elsewhere could also experience severe droughts.
IPCC scientists also said that global warming will not trigger a shutdown within the next 100 years of the North Atlantic Ocean current that keeps Northern Europe temperate, though they do not predict if it might occur in future centuries. In a similar vein, the authors concluded they did not have sophisticated enough computer models to project how much melting of the Greenland ice sheet would boost sea levels over the next century, but they suggested that over several centuries the ice sheet's disappearance could raise sea levels by a devastating 23 feet.
"Every government in the world signed off on this document, including the U.S.," World Bank chief scientist Robert T. Watson is quoted saying. Watson added that compared with the 2001 report, "the difference is now they have more confidence in what they're doing."