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

Here are seven ways of understanding the IPCC’s newest climate warning.

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 at 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 finds. 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 at a global scale—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 policymakers worldwide. And to reallysucceed, 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.

Across 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 between 1961 and 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,” the IPCC says.

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 who 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.

This isn’t scary, necessarily, but it is strange. Whatever that kind of arrangement is, it doesn’t seem constrained within economics or agriculture or ecology. And this is the most daunting aspect of the new report. For the scientific community, this document is a milestone because it assumes that land is scarce and precious. Climate researchers, for decades, have sometimes talked about land like it is a limitless global sponge capable of cleaning the worst mess in human history. A recent high-profile study, for instance, cheerfully suggested soaking up most of the planet’s carbon pollution by planting 1.2 trillion trees across 2.2 billion acres worldwide. It was impressive research, but immediately sold to the public as: The Solution to Climate Change.And there’s a problem with that. Those 2.2 billion acres—an area roughly the size of the continental United States—are already in use. They comprise, in large part, the planet’s most productive farmland! And in the decades to come, that farmland is going to be very useful if we hope to feed the 9.8 billion people who will soon reside on the planet.

4. In some ways, this is the most unavoidably political document that the IPCC has ever published. Its report last year, on the dangers of global warming beyond 1.5 degrees Celsius, called for an unprecedented transformation in the globe’s energy system. It demanded a rapid switch to carbon-free energy systems. But talking about the energy system is, in this context, relatively easy. No one’s ever gone to war over electric cars or renewable portfolio standards. But land is… land is different. It is home and the possibility of home. The relationship between people and land is the most treasured and unresolved idea in global politics. As the IPCC says, land “provides the principal basis for human livelihoods and well-being, including the supply of food, freshwater and multiple other ecosystem services, as well as biodiversity.” Another authority put it like this: “Cursed is the ground for thy sake… By the sweat of your face you shall eat bread, till you return to the ground, for out of it you were taken.” Chemically speaking, of course, we are mostly water. But everything we love about ourselves is solid, and therefore made of land.

Accordingly, everyone has opinions about it. Somewhat notoriously in climate circles, the final summary of every IPCC report is written by the world’s worst committee process. Over a marathon five days, the lead scientific authors sit at the front of a room and painstakingly read every line of the document to every national delegation who cares to attend. At any time, any delegation can more or less raise any issue with any word, and before the report can be published, every country’s delegation must acquiesce to it in full. Historically, oil-producing countries like Saudi Arabia use this process to raise one concern after another, bogging down the proceedings and effectively excising the strongest language from the final document.

But the process this time, which took place in Geneva, unfolded differently. The world’s developing countries might normally raise few issues with the IPCC’s initial proposed language. In this report, they asked for changes to line after line, according to Doreen Stabinsky, an environmental-politics professor at the College of the Atlantic who observed the talks.

“A lot of countries want to make sure that they see themselves, and their specific interests and issues, in every single paragraph,” she told me this week. “Land is something that’s so local. People come with the land and food-security issues in their country. You can tell people in the room care really deeply about these questions, but it has made things incredibly slow. There’s also some really complex political issues at the center.”

The biggest of these issues: Land can’t really multitask.

5. Nearly every American knows what our peculiar national grid of farm and field looks like. During a drive across the Midwest, it rolls past, flipbook-like: field-field-road, field-field-road. During a coast-to-coast flight, it unfurls out the plane window like a vast Cartesian quilt, lines meeting lines at right angles, circles of irrigation locked within squares. This grid system, formally known as the Public Land Survey System, covers much of the land outside the 13 original colonies.

What every American may not realize is that this grid gives us a great advantage when thinking about area. Each of those grid squares is about one square mile. The Earth’s total land surface is about 52 million square miles. So we only get 52 million grid squares to work with as a species. While 52 million squares may seem like quite a lot, consider that each of them is worth incommensurately more than 1 dollar. At some point in the past $52 million might have seemed like quite a lot of money. But now it cannot buy a 10-foot tall sculpture of an orange balloon dog.

These 52 million grid squares cannot only service our needs. They are all the land, period. They must also hold the vast, lovely, unknowable thing that we call nature—every shady spot, every mountain stream, every sand dune. (The IPCC authors call this, somewhat dryly, “biodiversity and ecosystem services.”) Every grain of rice and cobalt mine, every sidewalk square and platypus has to take place somewhere on that 52 million.

These were the “really complex political issues” at the center of the IPCC talks. “Land can’t, at the same time, feed people, and grow trees to be burned for bio-energy, and store carbon,” Stabinsky said. “That conflict of what’s going to take priority as we face greater and greater climate challenges” defined the talks, she said. “There’s going to be more and more desire to try to use land to pull carbon out of the atmosphere, and that’s going to interfere with food production.”

In a way, this process previewed the more consequential negotiations—and, God forbid, conflict—to come. And the report tries to anticipate some of these. The authors conclude that some land must be used to remove carbon through the atmosphere through a process called BECCS, or bioenergy carbon capture and sequestration. BECCS involves growing vegetation, burning it for energy, capturing the exhaust before it reaches the atmosphere, and burying both the exhaust and the charcoal underground. But very little land should be used for this, it says. Otherwise it will start to induce food shortages in poor countries.

6. Even if the authors mumble about the future, they can clearly denounce the present crisis: That system of 52 million is already badly damaged.

The planet’s land only absorbs carbon pollution today because of a great “natural subsidy,” said Louis Verchot, the report co-author. The 70 percent of ice-free land surface managed by people actually produces five gigatons of greenhouse gases per year. The remaining land surface—the 30 percent in nature’s control—sucks up 11 gigatons. So while the land surface absorbs about six gigatons of carbon on net, this has nothing to do with people.

“The land is out of balance in areas that we are managing,” Verchot said. “The biosphere is offsetting the carbon emissions, but that’s not a reason to call the land imbalanced.” He called this absorption an “additional gift of nature,” but it may be more apt to call it the final gift of nature. And at some point in the coming century—as more forests are felled and as demand for beef grows—this gift could become a curse, and the land will spew greenhouse gases into the air as ferociously as humanity does today.

Even before that reversal, this report confirms that the ill effects of climate change will arrive faster than scientists once thought. Under 1.5 degrees Celsius of planetary warming, the planet will face a high risk of food shortages, mass thirst, and rampant wildfires. Remember that land warms faster than the planet: A 1.5-degree-Celsius world would in fact be 3 degrees Celsius, or 5 degrees Fahrenheit, hotter on land.

Cynthia Rosenzweig, a senior research scientist at NASA and an author of the report, warned this week of “multiple bread-basket failure,” in which crops die across several major agricultural regions at the same time. She noted that crops in Europe had already suffered this summer under successive heat waves. Farmers in the Midwestern United States, meanwhile, have been hammered by spring and early-summer floods.

Avoiding 1.5 degrees Celsius of warming is a very aspirational if. While it’s not too late to stop our current course, humanity must put in extraordinary effort to hold warming to such a manageable level. If every car, pipeline, and power plant around today were allowed to keep operating until it broke down, and no other new fossil-fuel infrastructure was built, they would still lock in enough carbon emissions to shoot Earth well past 1.5 degrees of warming, according to a recent study.

At the same time, climate policy may do more than we realize. Timothy Searchinger, a land scientist at Princeton who was not involved in the new report, told me that the IPCC may undercount the benefits of land policy specifically. The panel does not always assume that farmers, for instance, will get better at capturing carbon if paid to do so, even though technology almost always improves in such circumstances, he said.

But on our current trajectory—and on any trajectory, frankly, where the United States does not adopt a serious climate policy—it’s far more likely that the planet will warm at least 3 degrees Celsius (5.1 degrees Fahrenheit) by 2100. That means that average land temperatures will be 10 degrees Fahrenheit hotter than they are today.

The IPCC warns that people who live on such a planet will face a “very high risk” of famine, water scarcity, and mass vegetation die-offs, according to the IPCC. Some of the people who will see that planet have already been born.

7. Let’s return to that one astonishing fact: that humans have integrated as much as one third of photosynthesis on land into the global economy. This statistic does not only capture the rice or broccoli or carrots on your plate, but the coffee seeds in your mug, the cotton fiber in your socks, the oak heartwood in your kitchen table, and the linseed oil in the linoleum floor.

What’s incredible about this claim is not only the scale of economic production that it entails. It’s that photosynthesis isn’t even the energetic part of the economy.What we call “the energy sector” still mostly consists of fossil fuels: oil, coal, and natural gas. Those three fuels generated 80 percent of the energy used in the United States in 2017, at least by a traditional accounting. Of course, fossil fuels are themselves just concentrated sunlight: The Permian oil basin in Texasis so named because it holds the gloopy product of photosynthesis during the Permian Period, more than 251 million years ago. And there’s a way of viewing climate change as a massive spending spree, the end-result of humanity spending down its 600-million-year inheritance.

But that’s not my point. To address climate change, we will need to reduce our use of fossil fuels, and replace energy generated in the past (by long-dead plants) with energy generated today (by wind turbines, solar panels, and uranium atoms). But this report adds: We must do all that in a house of only 52 million rooms, the vast majority of which already serve as someone’s bedroom, bathroom, or kitchen. And those 52 million rooms must stage not only the unending drama of the human family, but also—as far as we know—every other living thing in the universe.

How are you even supposed to talk about that? More than 30 years after climate change first became a political issue, it feels like we are still figuring it out. This report gets us closer. It makes clear that climate change isn’t only about coal-fired power plants, or gas-guzzling cars; and it’s definitely not about littering or—God help us—recycling. It’s about the profound chemical and physical specificity of human life. You and I are not free-floating minds that move around the world through text messages, apologetic emails, and bank deposits. We are carbon-based creatures so pathetic that we need a lot of silent plants to make carbon for us.

Climate change requires us to alter the biogeochemical organism that we call the global economy on the fly, in our lifetimes. Such a task should command most of the time and attention of every economist, agriculturalist, investor,  executive, and politician—anyone who fancies themselves a leader in the physical workings of the economy, or whatever we call it. It is our shame, and theirs, that they don’t.

This article originally appeared in The Atlantic.

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