The Paris agreement is good for neither Paris nor Pittsburgh

President Donald Trump is defending his plan to withdraw from the Paris climate-change accord on nationalist grounds. Announcing the decision last week, he said he was “elected to represent the citizens of Pittsburgh, not Paris.” Vice President Mike Pence, in Iowa, said that Mr. Trump had shown he is “more concerned with Des Moines than Denmark.” (Someone on his team should have told him there’s a Denmark, Iowa.)

Administration officials sometimes go even further. Scott Pruitt, the administrator of the Environmental Protection Agency, has suggested that the accord was intentionally designed to handicap our economy. There is very little evidence for that view. If Mr. Trump believes it, why has he said that he wants to renegotiate the deal with the countries behind the plot?

There’s a stronger case for leaving the accord — even a stronger nationalist case. The costs of restricting energy use, as I wrote when Mr. Trump made the announcement, are likely to exceed the benefits of mitigating global warming. Climate change is expected to reduce global GDP by up to 4 percent by 2100. That’s a significant cost. Given that the world is also expected to be much wealthier by then, it makes more sense to devote resources to researching how to mitigate and adapt to the effects of warming than to discourage energy use. Paris style solutions are therefore not in our national interest.

The fact that almost all the other governments of the world favor the accord should not keep us from pursuing our interests. We should factor their views into our decision, because we have an interest in good relations with other countries. But sometimes our interests will counsel breaking with the rest of the world.

There are better and worse ways to do that. Withdrawal from the Paris accord is being taken as a sign of contempt for our European allies and of reflexive hostility to international cooperation, not of our resolution to make hard-headed judgments about our country's welfare. The decision might be leaving a different impression if Mr. Trump had not repeatedly treated NATO in cavalier fashion or mused about leaving the World Trade Organization. Leaving the accord would still be intensely controversial, but it would not fit into the same pattern.

A foreign policy based on the national interest also need not entail a public rhetoric that refers exclusively and narrowly to the national interest. The costs of energy restriction are likely to exceed the benefits for the whole world. That's what most opponents of the accord actually believe. We think it’s not in Pittsburgh’s interest, in other words, but it’s not in Paris’, either.

Criticism of Mr. Trump often dwells on matters of tone at the expense of substance. But sometimes, and especially in foreign policy, tone is substance. What the administration has been unable to teach, because it has yet to learn, is that nationalism does not have to be bumptious.