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It’s time to delete carbon from the atmosphere. But how?

We need less of this.
Enlarge / We need less of this.

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This week and next, government representatives are gathering in Glasgow for the United Nations Climate Change Conference, or COP26, the latest of an increasingly frantic string of meetings as humanity runs out of time to drastically reduce our greenhouse gas emissions. Everyone agrees that carbon is bad. And everyone agrees it’s hard to get rid of; carbon dioxide lasts up to 1,000 years in the atmosphere. The world even has a common goal: keeping global temperatures from reaching 1.5 degrees Celsius above pre-industrial levels, the boundary set by the Paris Climate Agreement.

But nations don’t agree on how we’ll get there: staving off the worst of climate change will require cutting carbon emissions and developing ways to pull them out of the atmosphere. Here are some of the options delegates will likely be discussing as COP26 continues.

The problem with net zero

You’ve probably heard of a sticky little concept known as net-zero emissions: if you put any carbon into the atmosphere, you have to take the same amount out. On Monday at COP26, India’s prime minister, Narendra Modi, announced that his country would reach that goal by the year 2070. Earlier this year, President Joe Biden said the United States would do the same by 2050, a goal the UK has also pledged to achieve.

It’s a popular idea, although it’s based on achieving the bare minimum. “I think the main reason we’re going to probably see a lot of discussion about it at COP26, and certainly going forward, is that the world continues to pay lip service to the idea of limiting warming to one and a half degrees,” says Zeke Hausfather, a climate scientist and the director of climate and energy at the advocacy group the Breakthrough Institute.

The problem with net zero is that it doesn’t mean that these countries will stop spewing greenhouse gases by those target dates. It just means that by that point, they won’t be adding any to the atmosphere in aggregate. Net-zero can be a cop-out, because it allows nations to keep polluting so long as they’re also capturing that pollution. It’s a bit like trying to drain a bathtub with the tap still running full blast.

It might even encourage nations to keep spewing greenhouse gases, so long as they’re also sequestering them. Or a country might make a big deal about offshoring its carbon-intensive industries like steel production, disavow all those emissions, and then just import those materials anyway. Corporations, too, aren’t incentivized to actually reduce their emissions if they can just buy carbon credits. “It is absolutely a very reasonable concern and something we all have to guard against,” says Angela Anderson, director of industrial innovation and carbon removal at the nonprofit World Resources Institute, “the temptation and certainly the desire by some interests in the fossil fuel industry to not have to reduce emissions to preserve their existing business plans.”

The nebulousness of how these international exchanges will work makes it very difficult to agree on what net zero even means. “The definition of what is net zero, nobody has the faintest idea,” says Janos Pasztor, executive director of the Carnegie Climate Governance Initiative. Broadly speaking, a net-zero nation should add and remove the same amount of carbon to the atmosphere, he continues, “but what that means, and how you measure it, and how you demonstrate it, that remains to be seen.”

And more crucially, these experts say, aiming for zero isn’t aiming low enough. We’ll have to remove some of the carbon that’s already in the atmosphere. “We’re almost certainly going to pass 1.5 in the next few decades,” says Hausfather. “And so the only way to get back down to 1.5° C is to actively suck carbon out of the atmosphere. There’s pretty much no other way to do it.”

“The reality is that we didn’t do what we should have done 30 years ago, which is to reduce our emissions back then enough so that we wouldn’t be in the situation where we are today,” agrees Pasztor. “Now it’s too late simply to reduce emissions.”

Carbon-capturing technologies

The US government seems to have gotten the message: on Tuesday, the White House announced the Carbon Negative Shot (a play on a “moonshot”), an initiative for accelerating the development of carbon-removal technologies. In a new report, the White House acknowledges that certain industries will stubbornly resist decarbonization—think manufacturing and rail transportation. “Because of this,” the report says, “removals of CO2 from the atmosphere will be critical to enable the United States to reach net-zero by 2050 and to achieve net negative emissions thereafter.”

Carbon-capturing technologies come in two main varieties. Carbon capture and storage, or CCS, means grabbing the emissions from fossil fuel power plants and storing them. Carbon dioxide removal, or CDR, involves free-standing machines that suck in air and pass it over membranes that pull out the CO2. (This technology is also called direct air capture.) Basically, capture and storage methods would sequester the emissions a nation is currently producing, while the air removal methods would sequester legacy emissions already in the atmosphere.

But what happens with that CO2 once it’s been captured? One option is to dissolve it in water—sort of like the world’s biggest glass of soda—and pump it underground into highly reactive basalt rock, which absorbs the carbon and locks it away. Injecting captured CO2 underground is a fairly permanent solution. (Unless a supervolcano blows all that material sky-high.)

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