A new global warming report issued Friday by the United Nations paints a near-apocalyptic vision of Earth's future: hundreds of millions of people short of water, extreme food shortages in Africa, a landscape ravaged by floods and millions of species sentenced to extinction.
Despite its harsh vision, the report was quickly criticized by some scientists who said its findings were watered down at the last minute by governments seeking to deflect calls for action.
"The science got hijacked by the political bureaucrats at the late stage of the game," said John Walsh, a climate expert at the University of Alaska Fairbanks who helped write a chapter on the polar regions.
Even in its softened form, the report outlined devastating effects that will strike all regions of the world and all levels of society. Those without resources to adapt to the changes will suffer the most, according to the study from the U.N.'s Intergovernmental Panel on Climate Change.
"It's the poorest of the poor in the world, and this includes poor people even in prosperous societies, who are going to be the worst hit," said Rajendra Pachauri, chairman of the IPCC, which released the report in Brussels.
The report is the second of four scheduled to be issued this year by the U.N., which marshaled more than 2,500 scientists to give their best predictions of the consequences of a few degrees increase in temperature. The first report, released in February, said global warming was irreversible but could be moderated by large-scale societal changes.
That report said with 90% confidence that the warming was caused by humans, and its conclusions were widely accepted because of the years of accumulated scientific data supporting them.
In contrast, the latest report was more controversial because it tackled the more uncertain issues of the precise effects of warming and the ability of humans to adapt to them.
"When you put people into the equation, people who can adapt and respond and change their behavior, it adds another layer of complication," said Gary Yohe, an economist at Wesleyan University who helped write the report.
But the report is also, in a sense, a more pointed indictment of the world's biggest polluters -- the industrialized nations -- and a more specific identification of those who will suffer.
Thus, some nations lobbied for last-minute changes to the dire predictions. Negotiations led to deleting some timelines for events, as well as some forecasts on how many people would be affected on each continent as global temperatures rose.
An earlier draft, for example, specified that water would become increasingly scarce for up to a billion people in Asia if temperatures rose 3.6 degrees Fahrenheit -- a point that previous studies have said is likely to be reached by 2100.
A table outlining how various levels of carbon dioxide emissions corresponded to increasing temperatures and their effects was also removed.
The actions were seen by critics as an attempt to ease the pressure on industrialized nations to reduce their emissions of carbon dioxide and other greenhouse gases that are gradually warming the planet.
Several scientists vowed afterward that they would never participate in the process again because of the interference.
"Once is enough," said Walsh, who was not present during the negotiations in Brussels but was kept abreast of developments with a steady stream of e-mails from colleagues. "I was receiving hourly reports that grew increasingly frustrated."
The report paints a bleak picture, noting that the early signs of warming are already here.
Spring is arriving earlier, with plants blooming weeks ahead of schedule. In the mountains, runoff begins earlier in the year, shrinking glaciers in the Alps, the Himalayas and the Andes.
Habitats for plants and animals, on land and in the oceans, are shifting toward the poles.
Nineteen of the 20 hottest years on record have occurred since 1980, according to previous studies. The report said that more frequent and more intense heat waves were "very likely" in the future.
In some places, warming might seem like a good thing at first.
For example, worldwide food production is expected to increase with the first few degrees of temperature rise. For a time, an expanded fertile zone in the higher latitudes could offset losses in the tropics.
But at a certain point, crops everywhere will suffer as drought spreads. By mid-century, rising temperatures and drying soil will turn tropical forest to savanna in eastern Amazonia, the report predicts.
In North America, snowpack in the West will decline, causing more floods in the winter and reduced flows in the summer, increasing competition for water for crops and people.
California agriculture will be decimated by the loss of water for irrigation, experts have previously said.
Water will come more often around the world in its least welcome forms: storms and floods.