A transformed China, conflicts in Ukraine and elsewhere, and intractable clashes over money have pushed the prospects of progress to a new low.

Global power is fractured. Temperatures have risen to record levels. Bitterness and anxiety are rising in vulnerable countries lashed by deadly heat and floods.

This week, as presidents and prime ministers assemble at the United Nations General Assembly, they confront a vastly different world from the one that existed nearly 10 years ago, when nations rich and poor found a way to rally together around a remarkable global pact.

In that agreement, the 2015 Paris accord, they promised to act and acknowledged a bare truth: Climate change threatens all of us, and we owe it to each other to slow it down. Countries agreed to nudge each other to raise their climate ambitions every few years, and the industrialized nations of the world — which had prospered from the burning

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