WASHINGTON — Global warming is likely to have a series of destabilizing effects around the world, causing humanitarian crises as well as surges in ethnic violence and illegal immigration, according to an assessment released Wednesday by U.S. intelligence agencies.
Rising temperatures could weaken already fragile regimes around the world and create a new set of national security challenges for the United States over the next two decades, the report warns.
"Climate change alone is unlikely to trigger state failure" during that period, said Thomas Fingar, chairman of the National Intelligence Council, in remarks prepared for a joint congressional hearing.
"But the impacts will worsen existing problems -- such as poverty, social tensions, environmental degradation, ineffectual leadership and weak political institutions," Fingar said.
The report represents the U.S. intelligence community's most comprehensive assessment to date of the long-term security consequences of global warming. It also marks a reluctant foray into a politically charged topic.
Democrats and environmental activists praised the assessment, calling it formal acknowledgment by a key part of the government that the threat of rising temperatures is real.
But the report was also criticized, particularly by skeptics of global warming and people who oppose using U.S. intelligence resources to track something as amorphous as the environment.
"I think it was a pathetic use of intelligence resources," said Rep. Peter Hoekstra (R-Mich.), the ranking Republican on the House Intelligence Committee.
Hoekstra said the study did little to expand government officials' understanding of global warming and its consequences.
The document "didn't add anything I didn't already know," he said.
According to the report, the effects of global warming are likely to be most severe in sub-Saharan Africa, the Middle East and Central and Southeast Asia. Its authors warn that less rainfall and more volatile weather could cut agricultural output in some regions of Africa by as much as 50%.
"We judge that economic refugees will perceive additional reasons to flee their homes because of harsher climates," Fingar said. "Many likely receiving nations will have neither the resources nor interest to host these climate migrants," who might be carriers of infectious diseases.
Overall, as many as 50 million additional people could be at risk of hunger by 2020, and as many as 1.2 billion people could suffer from "water stress."
Developed nations are likely to fare better, Fingar said, with some estimates predicting that agricultural production in the U.S. could increase during the next 20 years.
But the U.S. will also face a cascade of challenges and problems. The nation "will need to anticipate and plan for growing immigration pressures," Fingar said, noting that helping dense coastal populations in the Caribbean "will be an imminent task."
Fingar also said the U.S. infrastructure is in many ways ill-prepared for climate change and the prospect of intense storms and flooding.
"Two dozen nuclear facilities and numerous refineries along U.S. coastlines are at risk and may be severely impacted by storms," he said.
The study relied on calculations and projections made by the United Nations' .
The report does not address global warming's potential effect on terrorism. A privately funded study completed by the Center for Naval Analyses last year concluded that climate change could "foster the conditions for internal conflicts, extremism and movement toward increased authoritarianism and radical ideologies."
The report can be found at http://www.dni.gov/testimon .