The world’s richest countries, which have contributed by far the most to the atmospheric changes linked to global warming, are already spending billions of dollars to limit their own risks from its worst consequences, like drought and rising seas.But despite longstanding treaty commitments to help poor countries deal with warming, these industrial powers are spending just tens of millions of dollars on ways to limit climate and coastal hazards in the world’s most vulnerable regions—most of them close to the equator and overwhelmingly poor.Over the last few decades, as scientists have intensified their study of the human effects on climate and of the effects of climate change on humans, a common theme has emerged: in both respects, the world is a very unequal place.In almost every instance, the people most at risk from climate change live in countries that have contributed the least to the atmospheric buildup of carbon dioxide and other greenhouse gases linked to the recent warming of the planet. Those most vulnerable countries also tend to be the poorest.And the countries that face the least harm—and that are best equipped to deal with the harm they do face—tend to be the richest.