Washington A key element of the second major report on climate change being released Friday in Belgium is a chart that maps out the effects of global warming, most of them bad, with every degree of temperature rise.
There's one bright spot: A minimal heat rise means more food production in northern regions of the world.
However, the number of species going extinct rises with the heat, as does the number of people who may starve, or face water shortages or floods, according to the projections in the draft report obtained by The Associated Press.
Some scientists are calling this degree-by-degree projection a "highway to extinction."
It's likely to be the source of sharp closed-door debate, some scientists say, along with a multitude of other issues in the 20-chapter draft report from the Intergovernmental Panel on Climate Change. While the wording in the draft is almost guaranteed to change at this week's meeting in Brussels, several scientists say the focus won't.
The final document will be the product of a United Nations network of 2,000 scientists as authors and reviewers, along with representatives of more than 120 governments as last-minute editors. It will be the second volume of a four-volume authoritative assessment of Earth's climate being released this year. The last such effort was in 2001.
Andrew Weaver, a climate scientist with the University of Victoria in British Columbia, said the chart of results from various temperature levels is "a highway to extinction, but on this highway there are many turnoffs. This is showing you where the road is heading. The road is heading toward extinction."
Weaver is one of the lead authors of the first report, issued in February.
While humanity will survive, hundreds of millions, maybe billions of people may not, according to the chart - if the worst scenarios happen.
The report says global warming has already degraded conditions for many species, coastal areas and poor people. With a more than 90 percent level of confidence, the scientists in the draft report say manmade global warming "over the last three decades has had a discernible influence on many physical and biological systems."
But as the world's average temperature warms from 1990 levels, the projections get more dire. Add 1.8 degrees Fahrenheit - 1 degree Celsius is the calculation scientists use - and between 400 million and 1.7 billion extra people can't get enough water, some infectious diseases and allergenic pollens rise, and some amphibians go extinct. But the world's food supply, especially in northern areas, could increase. That's the likely outcome around 2020, according to the draft.
Add another 1.8 degrees and as many as 2 billion people could be without water and about 20 percent to 30 percent of the world's species near extinction. Also, more people start dying because of malnutrition, disease, heat waves, floods and droughts - all caused by global warming. That would happen around 2050, depending on the level of greenhouse gases from the burning of fossil fuels.
"The worst stuff is not going to happen because we can't be that stupid," said Harvard University oceanographer James McCarthy, who was a top author of the 2001 version of this report. "Not that I think the projections aren't that good, but because we can't be that stupid."