Climate report faults humans for warming

Scientists from more than 110 countries are scheduled to release a landmark report this morning concluding that they are more than 90 percent certain that humans are the main reason for the world's recent temperature rise.

That's a significantly greater level of certainty than the Intergovernmental Panel on Climate Change expressed in its last report on global warming six years ago. The change could dramatically shift the global warming debate in the United States and elsewhere away from how much humans are responsible for the world's heat rise to what should be done about it, researchers and political observers say.

"The observed widespread warming of the atmosphere and ocean, together with ice-mass loss, support the conclusion that it is extremely unlikely that global climate change of the past 50 years can be explained without external forcing, and very likely that is not due to known natural causes alone," said the 20-page report , a copy of which was obtained by the Associated Press.

The report will give the most definitive assessment yet about the expected impact of global warming this century -- from rising temperatures to rising sea levels -- if humans do not take steps to reduce emissions of carbon dioxide and other heat-trapping gases from power plants and cars.

"This will be a benchmark for governments to debate possible actions," said Raymond S. Bradley, director of the Climate System Research Center at the University of Massachusetts at Amherst who saw early versions of the report.

Past IPCC reports have influenced governments to try to lower heat-trapping gases in the atmosphere, in part by signing the Kyoto Protocol, a multi nation pact that assigns mandatory emission targets for each nation that signs on. The United States in part has refused to participate because the agreement does not include such developing countries as China.

The new report will say rising temperatures are "very likely" human-caused -- a phrase that reflects more than 90 percent certainty -- according to Bradley and news reports based on leaks of drafts. The last report in 2001 said it was "likely" humans were responsible, which means the panel was more than 66 percent sure.

Today's announcement comes at a pivotal moment. The Democratic-led Congress has pledged to address climate change and US Representative Edward J. Markey of Malden is chairman of a subcommittee that will tackle the issue.

Yesterday, US Senators John F. Kerry of Massachusetts and Olympia J. Snowe of Maine reintroduced bipartisan legislation to reduce emissions of greenhouse gases from all sources to 65 percent below 2000 levels by 2050. And President Bush, who has long questioned the science behind global warming, made a passing reference to the "serious challenge of global climate change" in his State of the Union address last week.

"The debate about climate change has rapidly moved from 'if' to 'when,' " Markey said yesterday about the new report. " It falls to this Congress to meet this challenge by moving aggressively to transition away from forms of energy which have the capacity to destroy the planet as we know it."

The climate change panel, convened by the United Nations and World Meteorological Organization, is made up of thousands of scientists who analyze the science about climate change and issue a comprehensive report about every five years. Yesterday, bleary-eyed representatives from scores of countries were attempting to finish a secret line-by-line reading in Paris of a summary document that every country had to sign off on before it could be released.

News accounts about the report say it includes projections that worldwide temperatures will rise 3.6 to 8.1 degrees Fahrenheit by 2100 and possibly higher. In the last century, temperatures rose about 1 degree. Heat waves and fierce rainstorms will become more common by 2100 as well, the report says.

Scientists on the panel said yesterday that even if humans stopped putting carbon dioxide and other heat-trapping gases into the atmosphere, it would take more than a century for the climate to stop warming because the gases persist so long.

The report is a summary for policy makers of the physical evidence for climate change. It is the first of four installments to be released this year: In April, the panel will report on regional impacts of climate change and in May it will report on what the world can do to help solve the problem. Later in the year, the panel will issue a final report pulling together all its findings.

While the basic findings in today's report are not expected to be controversial among scientists, there probably will be vigorous debate about its conclusions on the impact of global warming on hurricanes and rising sea levels.

The report said global warming has made stronger hurricanes, including those in the Atlantic Ocean, Leonard Fields, the Barbados delegate, and others told AP.

The report also said that an increase in hurricane and tropical cyclone strength since 1970 "more likely than not" can be attributed to man-made global warming. The scientists said global warming's connection varies with storms in different parts of the world, but that the storms that strike the Americas are influenced by global warming.

That conclusion contradicts a World Meteorological Organization statement in December that said there wasn't enough evidence to draw a link.

Controversy about sea level projections has been percolating for more than a month. On sea levels, the report projects rises of 7 to 23 inches by the end of the century. That could be augmented by an additional 4 to 8 inches if recent surprising polar ice sheet melt continues.

But many scientists have warned that the projections are still too cautious, arguing that sea level rise could be closer to 3 to 5 feet because of ice sheet melt.

A report led by a German scientist released online by the journal Science yesterday showed that the climate panel's 2001 projections that sea level would rise less than 2 millimeters a year had been surpassed, to 3.3 millimeters a year between 1990 and 2006.

Material from the Associated Press was used in this report. Beth Daley can be reached at bdaley@globe.com. To view a summary of the IPCC report, go to www.ipcc.ch.