But the odd little box Lackner has come up here to check could take things a big step further. If it works on a bigger scale, this box could make the university a negative emitter — actually reducing the amount of carbon in the air by pulling some of it out again.

Lackner’s box is part of a new wave of technology aimed at turbocharging efforts to head off climate change. Such devices had been a pipe-dream until recently, but more and more, they are being seen as indispensable. That’s because the goals set at last year’s Paris accord on climate change, of keeping the planet’s warming “well below” 2 degrees Celsius, may not be achievable unless such technology comes to fruition.

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Solar power and electric cars won’t be enough, say scientists. Humans may have to somehow clean carbon out of the air, the way that trees do naturally but at a gigantic scale.

“If you want to balance the books at this point, I don’t think you have a choice but to pull CO2 back that has already made it out,” Lackner said. “Or is about to make it out, because we are not overnight shutting down all the coal plants.”

But that turns out to be very hard to do. There are a wide variety of ideas for getting carbon out of the air — from little boxes like Lackner’s to specialized power plants that burn renewable biomass and stow the carbon away. But they all have costs and downsides — and they’re all part of a race to see whether any such technology can really be big enough, and cheap enough, to make a difference.

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From the air, or from a smokestack?

The device that Lackner’s using to capture carbon dioxide doesn’t look like much: A transparent box with what resembles two stacks of lasagna noodles that can be lowered into it. The “pasta” actually contains what Lackner calls a sorbent – an absorptive material. It’s made up of a hard plastic resin – a synthetic analogue of natural substances like amber — that has been crushed into tiny pieces and then embedded in strips of softer plastic. And Lackner has shown that in the open air, it binds to that invisible gas that has caused the world so much trouble — carbon dioxide — and so acts as a kind of sponge to pull it out of the atmosphere.

The need for “negative emissions” technologies like the one at Arizona State — one of the first universities to establish a center for research in this area — comes down to a simple matter of math.

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With the planet already about 1 degree C warmer than in pre-industrial times, scientists have roughly calculated the remaining carbon “budget” for how much we can emit while still keeping below a 2-degree increase. And it’s extremely tight – well under 1,000 additional gigatons (or billion tons) of carbon dioxide. The world emits about 32 gigatons annually from energy use alone.

Staying under 1.5 degrees, an even more ambitious Paris target, is even harder – some might say impossible unless massive amounts of carbon can be removed from the air.

There is no shortage of ideas for how to do that, but “all of them face significant challenges today,” said Noah Deich, executive director of the Center for Carbon Removal at the University of California-Berkeley, another university exploring the area. “There’s no silver bullet, there’s no clear winner.”

Those trying to suck carbon dioxide directly out of the air include not only Lackner but also a number of startups. One firm, Carbon Engineering, has created a plant in Squamish, British Columbia, that is currently capturing a ton of carbon dioxide from the air per day using a liquid rather than solid sorbent, according to Geoff Holmes, the company’s business development manager. (One funder — Bill Gates.)

Direct air capture has its advantages – your sorbent can passively sit there, pulling in carbon dioxide, all the time. You can locate it virtually anywhere. And you aren’t just pulling in emissions from one source, like coal — you could just as well be pulling back emissions from cars or airplanes.

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But the approach also has downsides. Critics have repeatedly claimed, for instance, that it will have prohibitive costs.

“I’m skeptical there is a technology that will cheaply capture CO2 at 400 parts per million when it’s expensive to do at 400,000 parts per million in a smokestack,” says Rob Jackson, a professor of Earth sciences at Stanford University who has researched negative emissions. “It’s tougher thermodynamically. Carbon dioxide in air is a thousand times less abundant.”

Jackson and other researchers have studied what is perhaps the leading current idea for how negative carbon emissions are supposed to happen, and it’s very different. It’s called bioenergy with carbon capture and sequestration, or “BECCS.”

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The idea here is that you would pair two existing technologies: Growing corn, trees or other forms of biomass to burn in power plants, and then storing the burned-off carbon in the ground instead of letting it escape into the air. When the plants regrow , they would pull carbon dioxide out of the air again, and the net result would be a removal of carbon dioxide from the atmosphere.

One form of BECCS is quite far along. A project involving the Department of Energy, agricultural giant Archer Daniels Midland and University of Illinois researchers has already been able to remove about a million tons of carbon dioxide from the process of making corn-based ethanol and sequester it in Illinois sandstone layers 7,000 feet below the ground, according to Sallie Greenberg, a scientist with the Illinois State Geological Survey who works on the project.

But Lackner and other researchers think that BECCS may have an Achilles heel. Namely, the amount of land required to grow enough trees or corn to remove carbon at a planetary scale would be enormous.

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One recent study, for instance, found that in order to offset about a third of current global carbon emissions, you would need to cover the entire lower 48 states in BECCS projects.

Yet another negative emissions idea, simply planting huge amounts of trees where they currently do not exist, faces a similar hurdle. There’s no doubt more trees means less carbon dioxide in the atmosphere. Yet once again, vast areas could be required — and in the future, people will need even more land to grow food than at present.

Some researchers advocate a completely different approach, called “enhanced weathering.”

Scientists have long known that over vast time periods, carbon is removed from the atmosphere by becoming embedded in rocks. Here’s how it works: Rainwater contains some carbon from the atmosphere in the form of carbonic acid. As it falls on certain types of rocks, they break down or “weather,” and the interaction eventually leads to the formation of a carbonate — such as limestone — with the carbon locked inside.

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However, the process is very slow. “You can wait about 100,000 years and then nature mops up all of our CO2,” Lackner said.

The idea is to speed up this process by crushing silicate rocks like olivine, and spreading them over landscape surfaces to get rained upon. Sounds simple, but it takes a lot of money and energy to mine and then crush rocks, and the fine dusts that result could also prove a major health hazard if people breathe them in.

It’s also expensive. A recent study estimated a price of between $60 trillion and $600 trillion to remove 50 parts per million of carbon dioxide from the planet’s atmosphere in this manner.

Out of the greenhouse and into the greenhouse

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Lackner and his colleagues are grappling with similar issues. Their box works well as a demonstration, but how do you pull carbon dioxide from the air affordably at a much larger scale — and then, what do you do with all that gas to keep it from ever getting back into the atmosphere again?

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A key property of Lackner’s device is that it gives back CO2 easily if you simply get it wet. When you lower the plastic strips down into the box and spray them with water, computer readings show carbon dioxide levels in the container spiking.

“That’s more than a cup of coffee of pure CO2 in there,” Lackner says, after the machine has been doing its work for more than an hour.

Downstairs in Lackner’s laboratory, meanwhile, the plastic sorbent has been formed into objects of many shapes —including a rough doormat, with lots of bristles extending from it. When this carbon-gobbling doormat is relatively full of CO2, the researchers insert it into a research chamber that contains a large indoor plant called Devil’s Ivy, a fan, and plenty of humidity.

The sorbent will, effectively, feed the plant carbon dioxide and help it grow.

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Lackner says the experiment is about “finding a temporary use” for some of the carbon dioxide that has been pulled from the air.

But in the long term, that carbon dioxide will have to be buried underground or, perhaps, stored in rocks. “My personal view is the true long term storage is mineral carbonates, which is some form of accelerated weathering,” Lackner says. But he thinks we’ll also need to just store carbon in the ground sometimes, too.

Such storage has already been explored, notably at the $6.6 billion Kemper Plant, a 582- megawatt power plant in Mississippi expected to start sequestering carbon later this year.

The plant will strip 65 percent of the carbon dioxide out of coal through a gasification process, and then pipe it 61 miles to oil fields where it can be injected into the ground in a process known as “enhanced oil recovery” (EOR). There, the CO2 helps push more oil out of ground – and ultimately, will be sequestered there when wells are sealed.

But even if the storage solution can be worked out, the problem with Lackner’s air capture approach has been that many studies have suggested that it would be extremely expensive.

The ultimate issue — cost

With all these technologies and ideas, then, the question becomes how to lower the cost and when the world will truly start investing. A boon to all of them, of course, would be setting a global (or for the U.S., national) price on carbon, thus making its removal more valuable.

Lackner, for his part, thinks that with a $ 10 million R&D investment, he can scale up to a device that will remove a ton of carbon dioxide from the air per day. These devices will then get much cheaper once they’re mass produced, he says.

A ton per day may not sound like much, but as Lackner points out, it’s way more than the average person emits in a year in carbon dioxide though behaviors like driving. That total is 17 tons per year in the U.S., according to the World Bank — so the device would, in effect, offset the emissions of around 21 people.

With the clock ticking on the goals of the Paris climate accord, and with scientists disturbed by accelerating climate change around the globe, it may be that no single approach is going to be the answer. The important thing, Lackner said, is simply to act.

“We already delayed, and we waited,” he said. “And now is the time to clean up.”

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