VALENCIA, Spain (AFP) — The Nobel-winning IPCC group of climate scientists on Saturday issued their starkest warning yet on global warming, prompting a UN demand for politicians to smash the deadlock on tackling the worsening threat.
In a panorama of the evidence, the Intergovernmental Panel on Climate Change (IPCC) declared that the impact of global warming could be "abrupt or irreversible" and no country would be spared.
UN Secretary General Ban Ki-moon appealed to political leaders to push for "a real breakthrough" at a key conference running on the Indonesian island of Bali from December 3-14.
"We cannot afford to leave Bali without such a breakthrough," he said, branding climate change as the "defining challenge of our age."
Global warming bore the seeds of "catastrophe" yet there was also hope, he said. "There are real and affordable ways to deal with climate change."
The new report is intended to act as a guide to policymakers for years to come.
It summarises three massive assessments published this year on the evidence for global warming, its impacts and the options for tackling the emissions that cause it.
The report said notably:
-- Evidence of the planet's warming was now "unequivocal" and the effects on the climate system could be "abrupt or irreversible."
-- Retreating glaciers and loss of alpine snow, thinning Arctic summer sea ice and thawing permafrost show that climate change is already on the march.
-- By 2100, global average surface temperatures could rise by between 1.1 C (1.98 F) and 6.4 C (11.52 F) compared to 1980-99 levels.
-- Sea levels will rise by at least 18 centimetres (7.2 inches). An earlier estimate of an upper limit of 59 centimetres (23.2 inches) does not take into account "uncertainties" about the impact of disrupted carbon cycles and melting icesheets in Greenland and the Antarctic, the new report says.
-- Heatwaves, rainstorms, tropical cyclones and surges in sea level are among the events expected to become more frequent, more widespread or more intense this century.
-- "All countries" will be affected by climate change, but those in the forefront are poor nations, especially small island states and developing economies where hundreds of millions of people live in low-lying deltas.
-- Reducing emissions can be met at moderate cost relative to global GDP, but the window of opportunity for quickly reaching a safer, stable level is closing fast.
"We need a new ethic by which every human being realises the importance of the challenge we are facing and starts to take action through changes in lifestyle and attitude," said IPCC Chairman Rajendra Pachauri.
"Every country in the world has to be committed to a shared vision and a set of common goals and actions that will help us move toward a much lower level of emissions."
Green groups said the IPCC had highlighted the dangers of warming more clearly than at any time in its 19-year history.
"This is the strongest document the IPCC has produced," said Hans Verolme, director of WWF's Global Climate Change Program.
The Bali conference, taking place under the UN Framework Convention on Climate Change (UNFCCC), is tasked with launching a two-year round of negotiations for intensifying cuts in carbon emissions beyond 2012, when current pledges run out under the Kyoto Protocol.
"This report is clear in its findings in terms of the scientific certainty, and the fact that we have so many technological solutions available that could go a long way to solving this problem in an affordable way," UNFCCC Executive Secretary Yvo de Boer told AFP.
"It makes it very difficult for politicians to say 'no' to a launch of negotiations."
EU Environment Commissioner Stavros Dimas said the report was "a stark warning that the world must act fast... the good news is that it also shows that deep emission cuts are both technologically feasible and economically affordable."
"The global community must respond to this scientific call for action by agreeing in Bali to launch negotiations on a comprehensive and ambitious new global climate agreement," he added.
British Prime Minister Gordon Brown paid tribute to "the IPCC's measured assessment" of an "urgent challenge."
"It is vital that we launch negotiations on a comprehensive global agreement on tackling climate change," he said.
Carbon pollution, emitted especially by the burning of oil, gas and coal, traps heat from the Sun, thus warming the Earth's surface and inflicting changes to weather systems.
Emissions are now spiralling, driven especially by carbon dioxide (CO2) spewed from coal-fired plants in fast-growing China and India, and Kyoto's present commitments will not even dent the problem.
Reducing emissions implies a cost in converting to cleaner energy or more efficient energy use.
Jim Connaughton, chairman of the Council of Environmental Quality and a top White House environmental advisor, said the United States believes there is no clear scientific definition of the dangers of climate change although it recognizes urgent action is needed.
"The scientific definition of that is lacking, and so we are operating within the construct of, again, strong agreement among world leaders that urgent action is warranted," he said late Friday during a conference call from a meeting in Valencia.
Head US delegate in Valencia, Sharon Hays, cited recent American studies made on the basis of the last IPCC report, in which US researchers stated "very clearly" that "value judgments" still have to be made in determining what the dangers of climate change really are.
"So the science simply can't tell us what that number is," Hays stated. "There are always going to be value judgments associated with it."
The United States continues to oppose establishing strict legal limits on greenhouse gas emissions.
Instead it is arguing for voluntary measures, new technologies and increased efforts to persuade fast-developing countries like China and India to do their share of regulating greenhouse gases.
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