The Editorial Board

USA TODAY

Not all that long ago, leading Republicans took strong positions on climate change. Sen. John McCain of Arizona, the party's 2008 presidential nominee, co-authored legislation to cap greenhouse gas emissions. And former Arkansas governor Mike Huckabee presented the fight against global warming as a religious cause.

These days, it's difficult to find a Republican candidate willing to speak out in favor of doing something. Anyone who does so risks defeat in GOP primaries, where ardent climate change skeptics hold sway.

This is a problem for the country, indeed the world.

The National Climate Assessment, released this week, adds to a mounting and overwhelming body of evidence that the effects of rising temperatures are here and now — and that even higher sea levels, more extreme weather and water shortages are in our future if nothing is done.

Addressing the threat won't be easy, or popular. But denying that a problem even exists — which is common among the most vocal of Republicans — risks branding the party as one that is anti-science and refuses to participate in constructive governance.

As a way of getting back to where it was a few years ago, the Republican Party might want to start with three basic questions: Is the globe warming? Is the change primarily caused by human activity? And, if so, what can and should be done about it?

The first question ought to be beyond dispute at this point. The new climate assessment found that U.S. temperatures have warmed 1.3 to 1.9 degrees since 1895, with most of the increase coming since 1970. Sea levels have risen a foot or more in some U.S. cities, flooding rainstorms have increased in the Northeast and droughts have worsened in the West.

The second question is a bit more complicated. The climate is always changing because of natural variability and factors such as volcanic activity and solar radiation. Even so, 97% of climate scientists agree that the burning of fossil fuels is the primary driver of the warming observed in recent decades.

Should policy really be based on the minuscule chance that they're wrong?

The third question, though, is far more difficult to answer. New limits on emissions of greenhouse gases such as carbon dioxide and methane, needed to prevent global warming from getting totally out of hand, would likely have a dampening effect on the economy, at least in the near term. It's not an appealing prospect for voters, who've shown little willingness to sacrifice now to protect future generations.

What's more, unilateral U.S. action would have little effect if reluctant industrializing countries, particularly China, cannot be persuaded to act as well.

In that context, what to do — and at what cost — is a debate worth having.

Given the increasing scientific certainty about global warming, and the likelihood that public opinion will shift in the face of ever more compelling evidence, Republicans should be thinking of ways of getting out in front of the issue.

Otherwise, like climate change itself, it will overtake them before they can react.

USA TODAY's editorial opinions are decided by its Editorial Board, separate from the news staff. Most editorials are coupled with an opposing view — a unique USA TODAY feature.