Rising sea levels could swamp low-lying countries, causing mass migrations and conflicts over land, the report's authors warned. Meanwhile, water shortages and flooding could lead to or worsen political conflicts and conflicts over food and water -- and the United States could be drawn into these conflicts.
"Climate change exacerbates already unstable situations," former U.S. Army Chief of Staff and study co-author Gordon Sullivan told Associated Press Radio. "Everybody needs to start paying attention to this."
The possible military and political changes will come over the next 30 to 40 years, according to the report.
"Unlike the problems that we are used to dealing with, these will come upon us extremely slowly, but come they will, and they will be grinding and inexorable," retired U.S. Navy Vice Adm. Richard Truly said in the report.
Other recent studies have come to similar conclusions. A March report by the Global Business Network found that rising sea levels and other climate change consequences could lead to strife in countries like Bangladesh, parts of which may become uninhabitable.
"Just look at Somalia in the early 1990s," Peter Schwartz, one of the authors of that study, told the New York Times. "You had disruption driven by drought, leading to the collapse of a society, humanitarian relief efforts, and then disastrous U.S. military intervention. That event is prototypical of the future."
Climate scientists and experts generally agreed with the report's predictions.
"The evidence is fairly clear that sharp downward deviations from normal rainfall in fragile societies elevate the risk of major conflict," Marc Levy, associate director of the Earth Institute at Columbia University, told the New York Times. "It seems irresponsible not to take into account the possibility that a world with climate change will be a more violent world."
Some experts said the report's timeline might be too alarmist. Environmental scientist Terry Root of Stanford University told the Associated Press that some of the changes may take longer than 30 years to occur. However, she said that the report was "pretty impressive" and that the changes it predicts will occur sometime.
"We're going to have a war over water," Root told the Associated Press. "There's just not going to be enough water around."
The report was issued by the Center for Naval Analyses, a government-financed think tank.
The authors suggested several courses of action for the United States, including integrating climate change planning into national security and defense strategies, taking a stronger role in international efforts to curb climate change, and helping less developed countries develop strategies to deal with the effects of climate change.