The dry bed of the Hondo de Elche natural reservoir near Alicante, Spain, in a 2005 file photo.
The Earth is hurtling toward a warmer climate at a quickening pace, a Nobel-winning U.N. scientific panel said in a landmark report released Saturday, warning of inevitable human suffering and the threat of extinction for some species.
As early as 2020, 75 million to 250 million people in Africa will suffer water shortages, residents of Asia's megacities will be at great risk of river and coastal flooding, Europeans can expect extensive species loss, and North Americans will experience longer and hotter heat waves and greater competition for water, the report from the Intergovernmental Panel on Climate Change says.
U.N. Secretary-General Ban Ki-Moon said climate change imperils "the most precious treasures of our planet."
The potential impact of global warming is "so severe and so sweeping that only urgent, global action will do," Ban told the IPCC after it issued its fourth and final report this year.
The IPCC adopted the report, along with a summary, after five days of sometimes tense negotiations.
It lays out blueprints for avoiding the worst catastrophes — and various possible outcomes, depending on how quickly and decisively action is taken.
The document says recent research has heightened concern that the poor and the elderly will suffer most from climate change; that hunger and disease will be more common; that droughts, floods and heat waves will afflict the world's poorest regions; and that more animal and plant species will vanish.
The Summary for Policymakers, and the longer version, called the synthesis report, distill thousands of pages of data and computer models from six years of research compiled by the IPCC.
The information is expected to guide policy makers meeting in Bali, Indonesia, next month to discuss an agreement to succeed the Kyoto Protocol, which expires in 2012.
The panel was awarded the Nobel Peace Prize this year along with former Vice President Al Gore for their efforts to raise awareness about the effects of climate change.
The report is important because it is adopted by consensus, meaning countries accept the underlying science and cannot disavow its conclusions.
While it does not commit governments to a specific course of action, it provides a common scientific baseline for the political talks.
The U.N. says a new global plan must be in place by 2009 to ensure a smooth transition after the expiration of the Kyoto terms, which require 36 industrial countries to radically reduce their carbon emissions by 2012.
"There are real and affordable ways to deal with climate change," Ban said.
He said a new agreement should provide funding to help poor countries adopt clean energy and to adapt to changing climates.
The report says emissions of carbon, which comes primarily from fossil fuels, must stabilize by 2015 and go down after that. Otherwise the consequences could be "disastrous," said IPCC chairman Rajendra Pachauri.
In the best-case scenario, temperatures will continue to rise from carbon already in the atmosphere, the report said.
Even if factories were shut down today and cars taken off the roads, the average sea level will reach as high as 4½ feet higher than the preindustrial period, or about 1850.
"We have already committed the world to sea level rise," said Pachauri.
If the Greenland ice sheet melts, the scientists couldn't even predict by how many meters the seas will rise, drowning coastal cities.
Yet differences remain stark on how to control carbon emissions.
While the European Union has taken the lead in enforcing the carbon emission targets outlined in Kyoto, the United States opted out of the 1997 accord.
President Bush described it as flawed because major developing countries such as India and China, which are large carbon emitters, were excluded from any obligations. He also favors a voluntary agreement.
Sharon Hays, a White House science official and head of the U.S. delegation, said the certainty of climate change was clearer now than when Bush rejected Kyoto.
"What's changed since 2001 is the scientific certainty that this is happening," she said in a conference call to reporters late Friday. "Back in 2001 the IPCC report said it is likely that humans were having an impact on the climate," but confidence in human responsibility had increased since then.
"What's new is the clarity of the signal, how clear the scientific message is," said Yvo de Boer, the U.N.'s top climate change official. "The politicians have no excuse not to act."
Opening with a sweeping statement directed at climate change skeptics, the summary declares that climate systems have already begun to change.
Unless action is taken, human activity could lead to "abrupt and irreversible changes" that would make the planet unrecognizable.
Advocacy groups hailed the report as indispensable for the 10,000 delegates expected at Bali.
"We expect to see their personal copies of the Synthesis Report return from Bali, battered and worn from frequent use, with paragraphs underlined and notes in the margin," said Stephanie Tunmore of Greenpeace.