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 a thousand 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.
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 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.”
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.)
Another option is to turn it into fuel for airplanes and cargo ships. Both are hard-to-decarbonize parts of the transportation industry, given the size of the machines. This strategy isn’t actually carbon-negative, but carbon-neutral: The carbon is pulled out of the air, burned again, and returns to the atmosphere. It’s better than digging up more fossil fuels, and it reduces the demand for new fuel sources, but it’s still not an overall reduction.
Removing carbon from the atmosphere is not going to be cheap—far from it. Earlier this year, researchers called for a wartime-style investment in CDR technology, calculating that it’d take between 1 and 2 percent of global gross domestic product to build enough machines to pull 2.3 gigatons of CO2 out of the atmosphere a year. But at the moment, humanity is spewing 40 gigatons a year. We’d need 10,000 of these plants by the end of the century to even sequester 27 gigatons a year.
“We are so far from that, it is just not funny. So it requires acceleration, the kinds of things that governments can do by funding innovation, funding research,” says Pasztor. “Of course, the most important one to help financing would be a carbon price.” That is, to slap a tax on emissions from businesses, especially utilities and oil and gas companies, and use the proceeds to develop systems for sucking that carbon out of the air. But the financial onus of funding carbon-eating devices should not fall on economically-developing countries, says Pasztor, given that ultra-polluting powers like the US got us into this mess in the first place.
Some might wonder if upgrading fossil fuel plants to capture carbon will ultimately suppress investments in renewables, like solar farms. But the cost of those once-pricey green alternatives is now crashing. “Even somewhere like China, if they have to choose between retrofitting coal plants and increasing their cost by 25 percent, versus building new clean energy, I think the latter is going to be cheaper going forward,” says Hausfather. “I think the economics of coal are getting to be bad enough these days.”
There is another way to sequester carbon: The planet is already doing it, and all we have to do is help it along. Forests inhale CO2 and exhale oxygen. The storage of carbon in plant matter, or even landscapes like Arctic peat, is sometimes called “green carbon.” Conservationists are also increasingly turning their attention to “blue carbon,” or coastal vegetation like kelp forests, seagrasses, and mangroves.
Protecting environments like these not only helps more plants sequester carbon, but it can lead to beneficial knock-on effects: More biodiversity, more tourism, and more vegetation that prevents erosion or absorbs the water from storm surges, which will be particularly useful in places affected by sea-level rise. “Sometimes the other advantages of the nature-based approaches—for sustainability and local employment—may be much more than the actual carbon saved,” says Pasztor.
Yet many of these natural carbon sinks are being threatened in ways that may lead them to release the greenhouse gas. “Unfortunately, climate change itself is threatening the permanence of storing carbon in forests, for example with wildfires,” says Anderson. Fires are becoming more massive in the Arctic and the American west, and other human activities, like farming and raising livestock, are also churning up soil in ways that release sequestered carbon.
Climate experts say there is definitely one wrong way to go about sequestering “green” carbon: Planting a single tree species across a landscape and calling it a day. This is a flaw in many carbon offset programs, in which a company or government pays another entity to plant trees to compensate for their emissions. This kind of planting is not an ecosystem—it’s a crop. Single-species communities can be less resilient to disease, and if the trees are not native to the region, they may not be well-adapted to fire. (Not all fires have to be catastrophic for forests; smaller fires clear out dead brush from healthy ecosystems, and plants and animals that have evolved in fire-prone regions have adapted to regular burns.)
The math also doesn’t quite check out; even planting a trillion trees won’t be enough to hit that 1.5 degree goal. And Hausfather suggests that this kind of easy out also disincentivizes companies from making bigger changes. “You have all these companies that are saying they’re carbon-neutral, who have only reduced their emissions like 15, 20 percent, because they’ve covered all the rest with cheap forestry offsets,” he says. “Once you’re carbon-neutral, and you get all the fun PR around that, there’s less of an incentive to actually reduce your emissions.”
Ryan Hanna, an energy systems researcher at UC San Diego, says that this is one of the big advantages of investing in carbon-eating machines over carbon offsets: It’s clear what that money is buying. With offsets, “corporations can go in and do lots of opaque accounting and engage in tricks,” says Hanna, who was lead author on the paper that called for the mass deployment of direct air capture technologies. “They can game the system.”
On the other hand, if you build a facility to capture carbon, he continues, “You have durable, measurable carbon removal, because you inject CO2 into a pipeline and you pump it underground, and you can measure by mass and by volume.”
If we’re going to avoid the worst of climate change, we’ll need technologies like these. But, ironically, if the delegates at COP26 don’t push hard for more drastic change, the existence of carbon capture technologies could become a sort of fig leaf that allows governments and corporations to keep pumping out emissions as usual, while aiming to do no more than reach net zero. And that will put the world between a CO2-infused basalt rock and a hard place.
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