Let’s say you’re a Republican who believes that climate change is a real problem, and that human activity is contributing to it. But you also believe the Democrats’ Green New Deal is a wildly unrealistic and politically untenable way to deal with the problem. What do you do?

Perhaps you do what Tennessee Sen. Lamar Alexander has done. You take advantage of the moment to propose a different strategy—still ambitious but more in the political mainstream, and with at least some hope of attracting bipartisan support.

To...