AMSTERDAM, Netherlands — Climate change could be one of the greatest national security challenges ever faced by U.S. policy makers, according to a new joint study by two U.S. think tanks.

The report, to be released Monday, raises the threat of dramatic population migrations, wars over water and resources, and a realignment of power among nations.

During the last two decades, climate scientists have underestimated how quickly the Earth is changing — perhaps to avoid being branded as “alarmists,” the study said. But policy planners should count on climate-induced instability in critical parts of the world within 30 years.

The report was compiled by a panel of security and climate specialists, sponsored by the Center for Strategic and International Studies and the Center for a New American Security. The Associated Press received an advance copy.

Climate change is likely to breed new conflicts, but it already is magnifying existing problems, from the desertification of Darfur and competition for water in the Middle East to the disruptive monsoons in Asia which increase the pressure for land, the report said.

It examined three scenarios, ranging from the consequences of an expected temperature increase of 2.5 degrees Fahrenheit by 2040, to the catastrophic implications of a 10-degree rise by the end of the century.

At the very least, the report said, the U.S. can expect more population migrations, both internally and from across its borders; a proliferation of diseases; greater conflict in weak states, especially in Africa where climates will change most drastically; and a restructuring in global power in line with the accessibility of natural resources.

Left unchecked, “the collapse and chaos associated with extreme climate change futures would destabilize virtually every aspect of modern life,” said the report, comparing the potential outcome with the Cold War doomsday scenarios of a nuclear holocaust.

“Climate change has the potential to be one of the greatest national security challenges that this or any other generation of policy makers is likely to confront,” said the report.

Among its contributors were former CIA director James Woolsey, Nobel laureate Thomas Schelling, National Academy of Sciences President Ralph Cicerone, President Bill Clinton’s former chief of staff John Podesta and former Vice President Al Gore’s security adviser Leon Fuerth.

The report listed 10 implications of climate change that policy makers should consider, including rising tensions between rich and poor nations, the backlash resulting from massive migrations, health problems partly caused by water shortages and crop failures, and concerns over nuclear proliferation as nations increasingly rely on nuclear energy.

The global balance of power will shift unpredictably as trade patterns change, it said. China’s importance in the climate equation will grow as it increases emissions of greenhouse gases, and Russia’s influence will increase alongside its exports of natural gas, the report said.

Attention began to focus earlier this year on the strategic consequences of climate change. But the latest report, more than 100 pages long, is among the most detailed analyses published so far on security aspects.