Yet when I asked Mr. Nutter what the American insurance industry was doing to combat global warming, his answer was surprising: nothing much. “The industry has really not been engaged in advocacy related to carbon taxes or proposals addressing carbon,” he said. While some big European reinsurers like Munich Re and Swiss Re support efforts to reduce CO 2 emissions, “in the United States the household names really have not engaged at all.” Instead, the focus of insurers’ advocacy efforts is zoning rules and disaster mitigation.

Last week, scientists announced that the concentration of heat-trapping carbon dioxide in the atmosphere had reached 400 parts per million — its highest level in at least three million years, before humans appeared on the scene. Back then, mastodons roamed the earth, the polar ice caps were smaller and the sea level was as much as 60 to 80 feet higher.

The milestone puts the earth nearer a point of no return, many scientists think, when vast, disruptive climate change is baked into our future. Pietr P. Tans, who runs the monitoring program at the National Oceanic and Atmospheric Administration, told my colleague Justin Gillis: “It symbolizes that so far we have failed miserably in tackling this problem.” And it raises a perplexing question: why hasn’t corporate America done more to sway its allies in the Republican Party to try to avert a disaster that would clearly be devastating to its own interests?

Mr. Nutter argues that the insurance industry’s reluctance is born of hesitation to become embroiled in controversies over energy policy. But perhaps its executives simply don’t feel so vulnerable. Like farmers, who are largely protected from the ravages of climate change by government-financed crop insurance, insurers also have less to fear than it might at first appear.

The federal government covers flood insurance, among the riskiest kind in this time of crazy weather. And insurers can raise premiums or even drop coverage to adjust to higher risks. Indeed, despite Sandy and drought, property and casualty insurance in the United States was more profitable in 2012 than in 2011, according to the Property Casualty Insurers Association of America.