“There is no Plan B because there is no Planet B,” Emmanuel Macron lectured Donald Trump — in English — when the American president withdrew from the Paris climate agreement last year. Well, apparently there is a Plan B after all. Macron stopped his fuel-tax increase after concluding that marginal carbon reductions aren’t worth kneecapping an economy and sacrificing his political career. Trump could have warned him.

The French president views stopping climate change as a grand legacy project, and he had hoped to use higher fuel taxes to discourage driving for the sake of slashing carbon emissions. It didn’t matter to him that French emissions already are very low on a per capita basis and further cuts to transport emissions would be extremely difficult to achieve. But this matters a great deal to lower-income rural voters whose use of cars for daily life and business was about to become much more expensive.

Those voters produced the yellow-vest movement — named for the safety gear they wear — that in turn has created a political crisis for Macron. What began as a few hundred thousand protesters scattered around the country became more than a million last weekend, including inexcusable rioting mobs in Paris.

Macron’s tax backtrack, which his government says is only for six months, might induce the protesters to return home. But the movement grew so large and garnered so much public sympathy that his entire economic-reform agenda is now in jeopardy. The fuel tax was not part of his election campaign.

Trump tried to warn the French leader, albeit indirectly. “No responsible leader can put the workers — and the people — of their country at this debilitating and tremendous disadvantage,” he said of the costs of the Paris climate deal when he announced America’s withdrawal last year. The point is that the public seems to understand better than progressive elites that the consequences of climate change, whatever they turn out to be, will be easier to confront the more prosperous the world is.

FROM AN EDITORIAL IN THE WALL STREET JOURNAL