The report was ordered by an influential US Pentagon adviser, but was covered up by US defence chiefs for four months, until it was obtained by a British newspaper.
The leak promises to draw angry attention to US environmental and military policies, after Washington's rejection of the Kyoto Protocol on climate change and President George Bush's scepticism about global warming - a stance that has stunned scientists worldwide.
The Pentagon report, commissioned by Andrew Marshall, predicts that "abrupt climate change could bring the planet to the edge of anarchy as countries develop a nuclear threat to defend and secure dwindling food, water and energy supplies," The Observer said on Sunday.
The report, quoted in the paper, concluded: "Disruption and conflict will be endemic features of life... Once again, warfare would define human life."
Its authors - Peter Schwartz, a CIA consultant and a former head of planning at Royal Dutch/Shell Group, and Doug Randall of Global Business Network based in California - said climate change should be considered immediately as a top political and military issue.
"Disruption and conflict will be endemic features of life... Once again, warfare would define human life"
It "should be elevated beyond a scientific debate to a US national security concern", they were quoted as saying.
Experts familiar with the report told the newspaper that the threat to global stability "vastly eclipses that of terrorism".
Some examples given of probable scenarios in the dramatic report include:
- Britain will have winters similar to those in current-day Siberia as European temperatures drop off radically by 2020
- By 2007 violent storms will make large parts of the Netherlands uninhabitable and lead to a breach in the aqueduct system in California that supplies all water to densely populated southern California
- Catastrophic shortages of potable water and energy will lead to widespread war by 2020.
Coming from the Pentagon, normally a bastion of conservative politics and focused on military and political strategy, the report is expected to bring environmental issues to the fore in the US presidential race.