If you ask climate modelers how humanity can avoid severe global warming — say, 2°C or more — most will say we need to do two big things. First, we'll need to reduce global greenhouse gas emissions down to zero by the end of the century. Second, since we've been so tardy in making those cuts, we'll also need to figure out how to pull some carbon dioxide back out of the atmosphere.

And that's ... a problem. We at least have some notion of how to cut emissions. But sucking carbon dioxide back out of the atmosphere? At the massive scale likely needed? No one really has a clue how to do that. It's a huge, embarrassing blind spot in climate policy.

The IPCC has estimated that, to stay below 2°C of warming, we'll need to zero out our emissions and start removing between 2 and 10 gigatons of CO2 from the atmosphere each year by 2050. For perspective, all of the world's forests and soils put together currently remove just 3.3 gigatons of CO2 each year. So imagine doubling or tripling that. Planting more trees could help, but we'll need sweeping new carbon-removal techniques on top of that.

Right now, we have only crude ideas of what that might entail. Perhaps we could harvest trees sustainably, burn them for energy, and bury the resulting emissions underground — a technology known as bioenergy with carbon capture and sequestration (BECCS) that, in theory, is carbon-negative. Or we could try to boost the carbon-absorbing capacity of soil. Or we could deploy giant machines to suck CO2 out of the air (known as "direct air capture"). But we don't yet know if these ideas are feasible. And surprisingly few people are even working on this.

That's where Noah Deich comes in. A former clean tech consultant, he noticed that hardly any industry groups or policymakers seemed to be focused on developing techniques that scientists have deemed crucial for saving the planet. So he recently launched the Center for Carbon Removal, with the aim of bringing together scientists, industry, and policymakers and figuring out whether there's a viable path for removing lots of CO2 from the air.

I called Deich to talk a bit more about carbon removal. He says we're still in the very early stages of figuring out what works and what doesn't. "No one," he notes, "has the answer right now." It's possible nothing will work. But we need to start figuring that out soon — or tackling climate change could prove vastly more difficult than we think.

Brad Plumer: What's the basic case for paying more attention to carbon removal?

Noah Deich: There are two pieces. One is that it looks very critical for avoiding significant global warming. If we are unable to stay within our emission budgets, there’s no way to stay below 2°C without negative emissions.

Second, more broadly, there are lot of negative emission systems out there that seem to be good sustainable opportunities for sustainable developments. There are a number of carbon-removal techniques in agriculture that lead to increased soil fertility and water retention in addition to carbon sequestration. I think we haven’t really thought about all these different opportunities today — so if we expand from just thinking about mitigation and adaptation to also thinking about carbon removal, that starts to unlock a lot of potential.

BP: When you look at the IPCC's big report, its climate models suggest we need staggering amounts of bioenergy with carbon capture and sequestration (BECCS) to avoid 2°C of warming — removing between 2 and 10 gigatons of CO2 a year from the atmosphere by 2050. Is that even remotely realistic? Can it even be done sustainably?

ND: The way I interpret those models, they're saying we'll need some portfolio of net negative emissions. We don’t necessarily know what technology will get us there. It could be BECCS. But we could also have a breakthrough in direct air capture or agricultural techniques that help sequester carbon in soils that can reduce the need for BECCS.

I think the key here is we need to analyze all those different opportunities and start to say which ones work, which ones have potential, and which ones don’t make sense for us to invest in because they won't be sustainable or won't get to scale. Right now we don't even have enough data to figure that out. We don’t have enough field trials or even basic science. Here in the United States, we have a single BECCS plant — ADM's ethanol facility in Decatur, Illinois, part of a Department of Energy consortium to do test geological sequestration.

Models are great, they can help us understand the potential for this technology, but we need to test whether the assumptions that go into those models around cost, performance, and sustainability actually work. Because if they don't, and we’re banking on this technology, then 10 to 20 years down the road, we could be in real trouble.

BP: What's the state of science around carbon removal?

ND: It depends on what you’re looking at. When you look at systems we’ve been analyzing for a long time, like forests, we have a good idea of how much carbon is sequestered in forests. But when it comes to biochar or other soil carbons, or agricultural soil carbon, we still have a long way to go to say what the net carbon balance looks like.

Then you have industrial-scale systems. There's a lot of science around things like geologic sequestration for carbon. Here, the big need is for technological innovation in things like direct air capture of CO2. Right now, there are only three companies working on these technologies, whereas if you look at solar there are hundreds. So we're very early on — there isn’t even enough information for what the cost curve for direct air capture or industrial scale carbon removal would look like, because we haven't built these.

BP: It seems like there's little incentive to build any sort of industrial device to remove CO2 from the atmosphere unless there's an explicit policy in place to subsidize it. Is that necessary for carbon removal to take off?

ND: At a large scale, that’s probably fair. But also remember, today we use about 100 million tons of CO2 in various industrial processes. The vast majority is for enhanced oil recovery [in which carbon dioxide is injected underground to pull up more oil out of wells], so the environmental impact there is questionable.

But there are also sodas, fragrances, fire extinguishers — all these little things that use compressed CO2. A lot of those people are paying $100 per ton for compressed CO2 today, particularly if they're far away from a natural source. So it seems like this could be a viable short-term market, an opportunity to start, though eventually you'd likely need additional policies.

BP: So what might those policies look like?

ND: Lots of different things. You could imagine various regulatory schemes that incentivize industrial agricultural practices that sequester carbon. Right now, the US Department of Agriculture pays farmers to conserve land — we could tweak those programs to incentivize further carbon sequestration through restoration of wetlands or grasslands.

Carbon pricing is one obvious route, if we could ever figure out how to do that. But in the absence of that, there are still a lot of other regulatory techniques. In renewable energy, we've relied on performance standards and non-carbon-pricing policy tools to catalyze development.

BP: What's the most interesting work being done right now on carbon removal?

ND: From a business perspective, the most interesting carbon-removal work today is being done on agricultural side — things like using biochar to increase a soil’s fertility or water-retention ability, or farming in a way that you raise cattle in a way that sequesters carbon in soil.

There's a strong business case for some of these techniques even without carbon pricing, especially as we get greater climate extremes and need things like greater soil resilience. What's critical here is to have better science on how much carbon actually gets sequestered — since don’t want to encourage techniques that don’t have much of benefit or can’t replicate outside of certain ecosystems.

BP: Could we really sequester enough CO2 in the soil through better agricultural techniques to make a difference, climate-wise?

ND: Yeah, the potential is very large, at least. The amount of carbon that remains in soil is significantly larger than the overall carbon that’s in the atmosphere. So there's a huge reservoir. The question is how much we have depleted over time [through agricultural practices] and how much we could potentially add back. Those are both uncertain.

BP: What about some of these industrial scale ideas — direct air capture? Is that really viable?

ND: When you talk about direct air capture, people often say you’re crazy. There's no reason to capture CO2 from ambient air, which is only about 0.04 percent CO2, when you could capture CO2 directly from the smokestack, which is about 10 to 20 percent CO2.

Still, a handful of companies are making exciting progress on technologies that can capture CO2 from the air. The problem is the price points are around $100 per ton to $300 per ton [and some estimates peg it at $1,000 per ton or more], which is an order of magnitude too high. But if they can bring that cost down, there's a lot of exciting opportunities there.

One example: A small startup in Switzerland called Climeworks has partnered with Audi to make fuel directly from ambient air. That's not sequestration, but it's a carbon-neutral fuel production process. If they could scale that up economically, that could lead to techniques for sequestration. So there are some companies flying in the face of conventional wisdom that this doesn't make sense.

BP: So how does your Center for Carbon Removal fit in here? What problems are you trying to solve?

ND: The big gap we’ve identified is that there needs to be a lot more support from industry and the policy world to develop carbon removal solutions. There's great urgency in the scientific community to do these things, but that hasn't translated over to the industry and policy communities that will be responsible for leading deployment.

So we're trying to get the conversation on carbon removal started in these circles, which eventually means changing policies, building industry consortia, figure out how to get carbon removal projects on the ground. So we can understand what this big portfolio of net negative emissions looks like. Because your questions — are these sustainable? what’s the potential? what’s the market? — are really critical. And we don't know.

So we have a threefold strategy. One is to produce research and analysis, aimed at industry and policy audiences. Second is convening events to bring together industry and policy folks. Third is getting people more engaged.

I think there's a lot of potential for negative emissions to expand the climate conversation politically and create new coalitions. You can bring in energy, industry, agriculture, forestry. Bioenergy CCS is a weird technology that combines renewable energy but also carbon capture — two places in which advocates have not seen eye to eye. In theory, they could have common interests, and that's what we want to test out.

But we want to get that discussion started and figure out what the right answer is. We know no one has the right answer right now.

Interview has been lightly edited for length and clarity.

Further reading