But unlike other sources of pollution—such as the burning of fossil fuels, which must be quickly reduced globally—land can’t just be shut down. It must be made into a tool in the climate fight. The report’s more than 100 authors, hailing from 51 countries, say that this will require immediate action from farmers, bankers, conservationists, and policy makers worldwide. And to really succeed, it will require hundreds of millions of affluent people in the Northern Hemisphere to change their diet, eating many more plants and much less meat—and especially much less red meat—than they do now.

These changes must happen fast, because land problems have a pesky way of metastasizing. Louis Verchot, a scientist at the International Center for Tropical Agriculture and an author of the new report, described the cascading consequences of warmer air temperatures at a press conference this week.

“As the biosphere gets warmer, we increase evaporation,” he said. “And as we increase evaporation, ecosystems dry out and burn when they normally wouldn’t do that. And when soils get dry due to increased evaporation, we get longer heat waves.” And longer heat waves, of course, make the biosphere warmer still, starting the cycle again.

Around much of the world, this cascade has already begun. Heat waves worldwide have gotten longer, hotter, and more common, according to the IPCC. Deserts are expanding toward the poles, while zones of colder weather are shrinking. Dust storms are kicking up more often. And evidence suggests that every year from 1961 to 2013, an additional 1 percent of the world’s drylands slipped into drought.

As I said, there are a lot of scary facts here.

3. Yet one fact—maybe the most important idea in the report—didn’t frighten me so much as leave me awestruck. It comes early in the document: “People currently use one quarter to one third of land’s potential net primary production for food, feed, fiber, timber and energy.”

It’s a lot of jargon. But here’s what it means. Recall from high-school biology that primary production is the conversion of sunlight into chemical energy via photosynthesis. Besides the tiny creatures that live in deep-sea heat vents and other extreme environments, all life on Earth derives its energy from the sun. You and I don’t get our energy directly from photosynthesis, but we eat plants—or things that ate plants—that do. Every major food chain on Earth begins with a plant, somewhere, humbly transfiguring photons into sugar.

This is the net primary production that the IPCC alludes to. It’s saying that the human demand for food, meat, clothes, and warmth now consumes at least 25 percent of the net product of photosynthesis on land. The free-wheeling, far-reaching maw of our material metabolism—that thing we normally call the global economy—devours as many as one out of every three sugar molecules made by dirt-bound plants, on net. Plants are one of the few things in the universe that can work this magic, as far as we know. And we have roughly hooked one out of every four of them into our planetary system of consumption and speculative exchange.