U.S. military officials increasingly view climate change as a “threat multiplier,” a factor that can aggravate poverty, political instability and social tensions. That, in turn, could foster terrorism and other forms of global violence while impairing America's military effectiveness. Rising seas, due mainly to Arctic ice melting, already threaten Naval Station Norfolk in Virginia, the world's largest naval base; dozens of other coastal installations also are at risk. Meanwhile, drought in some regions and record rainfall in others have forced millions of people to migrate across borders, adding to tensions in northern Africa, the Middle East and Southeast Asia. Defense Secretary James Mattis said climate change is affecting the stability of areas where U.S. troops are operating. President Trump, who has labeled climate change a “hoax,” now says he has an “open mind” on the issue. Some politicians and economists argue that the real danger to U.S. security lies in the erosion of jobs, trade and industrial productivity caused by the costs of unnecessary federal environmental regulations.