To curb climate change, we have to suck carbon from the sky. But how?

At McCarty Family Farms, headquartered in sun-blasted northwest Kansas, fields rarely sit empty any more. In a drive to be more sustainable, the family dairy still grows corn, sorghum, and alfalfa, but now often sows the bare ground between harvests with wheat and daikon. The wheat gets fed to livestock. The radishes, with their penetrating roots, break up the hard-packed surface and then, instead of being harvested, are allowed to die and enrich the soil.

Like all plants, cereal grains and root vegetables feed on carbon dioxide. In 2017, according to a third-party audit, planting cover crops on land that once sat empty helped the McCarty farms in Kansas and Nebraska pull 6,922 tons of carbon dioxide from the atmosphere and store it in the soil across some 12,300 acres—as much as could have been stored by 7,300 acres of forest. Put another way: The farm soil had sucked up the emissions of more than 1,300 cars.

"We always knew we were having a sizable impact, but to have empirical numbers of that size is inspiring to say the least," says Ken McCarty, who runs the farms with his three brothers.

Moves like this are among a host of often overlooked steps that scientists now say are crucial to limiting the worst impacts of climate change.

From planting more trees and restoring grasslands to using sophisticated machines with fans and filters to capture CO2 from ambient air, these far-ranging steps are all aimed at one thing: Sucking greenhouse gases from the sky.

The machines to do that are still cumbersome and expensive. But managing forests and grasslands and farms with an eye toward atmospheric carbon removal is often a matter of doing what we already know how to do, only better.

"We know how to deal with forests; we know how to store carbon in soil," says Richard Birdsey at Woods Hole Research Center. "These are strategies that are ready right now—things that can basically be deployed immediately."

A study last year in the Proceedings of the National Academy of Sciences led by a team from The Nature Conservancy suggests that the right incentives could drive the world to get up to a third of the carbon reductions it needs by 2030 simply by using nature better.

Other studies challenge those figures, but not the basic premise: It's not simply that we can use nature to help save the world—it's that we must.

Moral hazard or imperative?

In the three years since 195 nations committed in Paris to cap global temperature increases at 2 degrees Celsius—while also agreeing to aim for 1.5 degrees—a few things have become bracingly clear.

The world must quickly stop burning fossil fuels. And that is no longer enough.

Again and again, including in a major report published fall, the Intergovernmental Panel on Climate Change and other science bodies have reached a stark conclusion: Most paths to halting global temperature increases at 2 degrees—and every path to reach 1.5 degrees—rely in some way on adopting methods of sucking CO2 from the sky.

It is a significant about-face. For years many scientists dismissed or downplayed the most highly engineered CO2 removal strategies. Those techniques were often lumped in with more dangerous forms of "geoengineering," such as injecting sulfates or other aerosols into the stratosphere to reflect sunlight and cool the planet. Focusing money and energy on any such technological fix seemed both risky and fraught with "moral hazard"—a distraction from the urgent need to cut emissions by slashing use of coal, oil, and gas.

But now many see "negative emissions," as CO2 removal strategies are also called, as an essential bridge to a clean-energy future.

"CO2 removal has gone from a moral hazard to a moral imperative," says Julio Friedmann, senior research scholar at the Center for Global Energy Policy at Columbia University.

There are several reasons for the shift. For starters, attempting to set a hard target at 1.5 or 2 degrees gives the world an emissions cap. With carbon emissions from fossil fuels estimated to have risen 2.7 percent in 2018, we're clearly not moving fast enough to reduce emissions—or even in the right direction.

"The longer we have postponed drastic reductions, the more daunting the challenge of achieving those reductions in the necessary time frame," says Erica Belmont, a University of Wyoming engineering researcher.

Even if the developed world rapidly switched to clean fuels, poorer countries would likely take longer. Emissions from some industries, such as cement and steel production, will be hard to eliminate, and alternative fuels for air travel are expected to remain expensive for quite some time.

Rapid progress

The good news is that CO2-removal technology has advanced far faster than expected in the last decade, says Stephen Pacala, a Princeton professor who oversaw a study of carbon removal strategies published this fall by the National Academies of Science.

The costs of machines that directly capture CO2 from the air have fallen by two-thirds or more. Meanwhile, at least 18 commercial-scale projects around the world already capture CO2 from the smokestacks of coal or natural gas plants, storing it underground or even using it to create other products. Costs of that technology have dropped by half in a dozen years. While removing CO2 from smokestack gases is not the same as removing it from the ambient air—the former prevents new emissions, the latter cleans up old ones—both techniques require some means of sequestering CO2 after it’s captured. Additionally, advances in research and development from industrial carbon-capture can help drive innovation in efforts to pull old carbon from the atmosphere.

"Post-combustion carbon capture and direct air capture processes have significant components where know-how is transferable," says Christopher W. Jones, associate vice president for research at Georgia Institute of Technology.

Equally important, the political will to subsidize carbon removal appears to be growing. Even a GOP-led Congress hostile to climate change worked last year with climate hawks like Sen. Sheldon Whitehouse, D-Rhode Island, to approve a $50-a-ton tax credit for specific types of CO2 removal, including negative emissions techniques such as direct-air capture.

“We need to design and deploy technology to capture lots of carbon from our atmosphere at a pace never before seen," Sen. Whitehouse told National Geographic. "That’s why I’ve been pursuing legislation to help drive the development of that technology."

"You are a pessimist if you work on the science of climate impacts, because you see little action," Pacala says. "The people who know the most are the most freaked out. They've seen emissions go up and up andsee a train wreck coming."

But scientists studying negative emissions, Pacala continues, "have seen the most spectacular technological achievements in energy technology in the last 10 years. We've gone from having no tools to do this, to just seeing this unrelenting progress."

He and the other authors of the National Academies report concluded that a concerted multi-billion-dollar research and development push by government and the private sector might within 10 years produce market-ready technology that directly removes CO2 from ambient air on a massive scale.

But even evangelists such as Pacala and Whitehouse insist that direct air-capture technology can at most fill in the gaps in an overall effort to decarbonize the economy. It will never reach a scale that would save us from having to wean ourselves from fossil fuels—or from having to manage the land much better than we do now.

First, do no harm

The first step in improved land management is to halt practices that require carbon-removal in the first place, such as large-scale land clearing and burning. Halting deforestation in Indonesia and Brazil alone could reduce emissions equivalent to those produced by every car and light truck on the road in the United States.

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"Dealing with tropical deforestation is huge, huge, huge," says Katherine Mach, senior research scientist at the Woods Institute for the Environment at Stanford University.

Retaining trees does more than just pull carbon from the atmosphere. Since the Amazon produces its own moisture, tree loss can lead to drought and fire, which could quickly destabilize and flip the forest to another type of landscape—one that would release its stored carbon.

Replanting trees, on the other hand, could reduce atmospheric greenhouse gases even more. Simply restoring forests already chopped down in Brazil could draw about 1.5 billion metric tons of CO2 out of the air.

While trees grow fast in the tropics, forest restoration shouldn't be limited to remote places. In fact, managing most land in the U.S. with an eye toward carbon reduction—both limiting new emissions and looking for places to pull CO2 back out of the atmosphere—could achieve the equivalent of cutting the country's emissions by 21 percent, according to a recent study in Science Advances.

Managing land for carbon reduction would include restoring trees to native forests, slowing logging rotations on Southeast timberlands, and planting more trees in some 3,500 cities. But it also would mean better managing forests to reduce catastrophic wildfires, reconnecting tidal marshes cut off from the ocean, and restoring seagrasses. Cover crops would need to be added between plantings on every acre of corn, soil, wheat, rice, and cotton in the U.S.

It's ambitious—and essential to at least try, says Joe Fargione, science director for The Nature Conservancy and lead author of the recent study.

"The track that we're on with climate change is so dangerous that it requires an all-hands-on-deck approach," Fargione says. "This could buy us 10 years."

Many—but not all—of the actions envisioned by his team would require a price on carbon to motivate landowners to change behavior. And there are potential pitfalls.

Probably the most important one is that managing land for carbon reduction could conflict with managing it for food production. With global food demand set to increase substantially over the next few decades, restoring the wrong farm land back to native forest or grasslands could limit food availability and send price shocks through the system.

Then there is the obvious challenge of realizing the theoretical potential of natural carbon reduction, not just in the U.S. but on a globe covered by a tremendous diversity of landscapes and governed by a mosaic of rules and owners and political situations. In Brazil, for example, the new president-elect threatens to increase deforestation, not tree-planting. The situation in the U.S. is not necessarily easier.

"There are 11 million forest landowners just in the U.S," Birdsey says. "Getting 11 million families or entities to do anything—that's a big challenge. Most programs that try to get even 10 percent of potential landowners to participate fail."

That's why the National Academies study is far more conservative[RK11] than the research published by Fargione’s team in Science Advances. It assumes that forests and farms worldwide could realistically pull only 2.5 gigatons of CO2 from the atmosphere a year.

A massive buildout of a technique called bioenergy with carbon capture and sequestration—in which crops, wood, or waste biomass are burned for electricity or fuel, and the resulting CO2 is captured and stored—would double the amount of CO2 removed, the National Academies study says

Still, that would be a real achievement. Five gigatons of CO2 amounts to about half of fossil fuel emissions in the United States, the world's second-largest polluter.

Back on the farm

At McCarty Family Farms the move toward a carbon-friendlier operation was a slow evolution that highlights landowners' competing motivations.

The family relocated from eastern Pennsylvania to the Midwest almost 20 years ago. As its farms grew to 8,500 cows, the family began moving toward sustainability, but not for any single reason.

New research confirms that cover crops soften soils and make them richer, increasing yields. That also fights wind erosion, and much of the McCartys' land abuts highways, where dust blowing from fields can cause accidents. Plus, cover crops had been standard in Pennsylvania, because they kept rains from washing nutrients from fertilized fields into Chesapeake Bay.

"In western Kansas, cover crops are not common," McCarty says. "Water is scarce and a declining resource, and people historically viewed cover crops as a drain on water. Research shows it can help you capture more water, but it's hard to break old ideas."

Then, about six years ago, the McCartys contracted to supply milk to Danone North America—makers of Dannon yogurt—which, as part of a broader sustainability effort, has pledged to become carbon-neutral by 2050. The McCartys also committed to produce non-genetically modified goods. That meant staying connected to their cows' food. They began planting cover crops in earnest.

Danone didn't require the McCartys to adopt particular practices. "But they encourage, through a variety of means, the adoption, sharing and utilization of best practices in all aspects of our farm management," McCarty says.

The arrangement gives the dairy price stability. When times are tough—especially on dairies, 90 percent of which are family-owned—that makes a world of difference.

"The farm economy has been challenging for a number of years," McCarty says. "When you're fighting for sheer survival, it's difficult to think about 'value added' products."

Most American farmers, he adds, are much older than he is. At 36, he’s the youngest of four McCarty boys.

"The average age of the American farmer is up there, and often-times the belief in climate change and the willingness to try new practices is more common in younger generations," McCarty says.

"All we have to do is start"

Extending a carbon tax credit like the one Congress passed this year to farms and timber owners might make a difference

"That would be incredibly helpful," McCarty says.

The value of incentives to drive innovation is no secret. That's how renewable power went from a niche product to an energy staple in little more than eight years.

"Why is wind and solar so cheap? Because subsidies created a marketplace where capitalism could do its magic," Pacala says. Creating a similar marketplace for negative emissions while decarbonizing the economy could bring rapid change.

"Everyone in the U.S. needs to know: We largely have the technology to solve the problem," Pacala says. "All we have to do is start."