United Nations ? An international panel of scientists presented the United Nations with a sweeping, detailed plan Tuesday to combat climate change – a challenge, it said, “to which civilization must rise.”

Failure would produce a turbulent 21st century of weather extremes, spreading drought and disease, expanding oceans and displaced coastal populations, it said.

“The increasing numbers of environmental refugees as sea levels rise and storm surges increase will be in the tens of millions,” said panel co-chairwoman Rosina Bierbaum, a University of Michigan ecologist.

After a two-year study, the 18-member group, representing 11 nations, offered scores of recommendations: from pouring billions more dollars into research and development of cleaner energy sources, to mobilizing U.N. and other agencies to help affected people, to winning political agreement on a global temperature “ceiling.”

Their 166-page report, produced at U.N. request and sponsored by the private United Nations Foundation and the Sigma Xi Scientific Research Society, was issued just three weeks after the Intergovernmental Panel on Climate Change, an authoritative U.N. network of 2,000 scientists, made headlines with its latest assessment of climate science.

The panel expressed its greatest confidence yet that global warming is being caused largely by the accumulation of carbon dioxide and other heat-trapping gases in the atmosphere, mostly from man’s burning of coal, oil and other fossil fuels. If nothing’s done, it said, global temperatures could rise as much as 11 degrees Fahrenheit by 2100.