THE re-election of President Obama, preceded by the extraordinary damage done by Hurricane Sandy, raises a critical question: In the coming years, might it be possible for the United States to take significant steps to reduce the risks associated with climate change?

A crucial decision during Ronald Reagan’s second term suggests that the answer may well be yes. The Reagan administration was generally skeptical about costly environmental rules, but with respect to protection of the ozone layer, Reagan was an environmentalist hero. Under his leadership, the United States became the prime mover behind the Montreal Protocol, which required the phasing out of ozone-depleting chemicals.

There is a real irony here. Republicans and conservatives had ridiculed scientists who expressed concern about the destruction of the ozone layer. How did Ronald Reagan, of all people, come to favor aggressive regulatory steps and lead the world toward a strong and historic international agreement?

A large part of the answer lies in a tool disliked by many progressives but embraced by Reagan (and Mr. Obama): cost-benefit analysis. Reagan’s economists found that the costs of phasing out ozone-depleting chemicals were a lot lower than the costs of not doing so — largely measured in terms of avoiding cancers that would otherwise occur. Presented with that analysis, Reagan decided that the issue was pretty clear.