How to Understand the IPCC’s New Climate Warning – The Atlantic

Climate change could make water even more scarce in naturally dry areas, the report warns. Australia’s ranchers have struggled under a drought for years.Brook Mitchell / Getty 1. There is no shortage of scary facts in the major new report on climate change and land, a summary of which was released today by a United Nations–led scientific panel. Chief among them: For everyone who lives on land, the planet’s dangerously warmed future is already here. Earth’s land has already warmed more than 1.5 degrees Celsius (2.6 degrees Fahrenheit) since the industrial revolution, according to the Intergovernmental Panel on Climate Change. That’s the same amount of warming that climate activists are hoping to prevent on a global scale.

This spike makes sense, scientifically: Land warms twice as fast as the planet overall. Earth as a whole has warmed by only 0.87 degrees Celsius (1.5 degrees Fahrenheit) during the same period. But this increase makes the stakes of climate change clear: When scientists discuss preventing “1.5 degrees Celsius of global warming,” they are really talking about forestalling 3 degrees Celsius—or 5.1 degrees Fahrenheit—of higher land temperatures.

And land temperatures are what humanity usually cares about. Land, really, is what humanity cares about. That’s the point.

2. If the report has an overarching theme, it’s that land is extremely scarce, we need it for everything, and we are already using most of it. More than 70 percent of the planet’s ice-free land is already shaped by human activity, the report says. As trees are felled and farms take their place, this human-managed land emits about a quarter of global greenhouse-gas pollution every year, including 13 percent of carbon dioxide and 44 percent of the super-warming but short-lived pollutant methane.

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.

…(read more).

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