The study, published Wednesday in the journal Nature, found that global carbon storage capacity was 10 times less than previous estimates after ruling out geological formations where the gas could leak, trigger earthquakes or contaminate groundwater, or had other limitations. That means carbon capture and storage would only have the potential to reduce human-caused warming by 0.7 degrees Celsius (1.26 Fahrenheit) — far less than previous estimates of around 5-6 degrees Celsius (9-10.8 degrees Fahrenheit), researchers said.

“Carbon storage is often portrayed as a way out of the climate crisis. Our findings make clear that it is a limited tool” and reaffirms “the extreme importance of reducing emissions as fast and as soon as possible,” said lead author Matthew Gidden, a research professor at the University Maryland’s Center for Global Sustainability. The study was led by the International Institute for Applied Systems Analysis, where Gidden also is a senior researcher in the energy, climate and environment program.

The study is the latest knock on a technology, for years promoted by oil and gas industry, that has often been touted as a climate solution. Today, carbon capture is far from being deployed at scale, despite billions of dollars in investments around the world, and the amount of carbon currently captured is just a tiny fraction of the billions of tons of carbon dioxide emitted every year.

Challenging assumptions

The 2015 Paris Agreement called for limiting average global temperature increase to 2 degrees Celsius (3.6 degrees Fahrenheit), but ideally below 1.5C (2.7F), compared to the early 1800s.

Many scenarios for achieving that have relied on carbon removal and storage, assuming the potential was “very large” because previous estimates didn’t account for vulnerable areas that might not be suitable, said study co-author Alexandre Koberle, a researcher at the University of Lisbon.

“That was never systematically challenged and tested,” said Koberle, adding that the study was the first to examine which areas should be avoided, leading to what they call a “prudent potential” that minimizes risks to people and the environment.

That’s not to say that carbon capture and storage isn’t important to keep global temperatures in check — but countries must prioritize how they use the limited storage and do so in conjunction with fast and deep emissions reductions, researchers said.

The technology ideally should be used for sectors that are difficult to decarbonize, such as cement production, aviation and agriculture, rather than to extend the life of polluting power plants or to prolong the use of oil and gas, Koberle said.

Industry officials defended carbon capture and storage as having an inherently low risk and say emerging technologies, such as storing carbon dioxide in basalt formations where it becomes mineralized, could dramatically increase total storage volumes.

What’s more, its use is “not optional if we hope to address global warming,” said Jessie Stolark, executive director of the Carbon Capture Coalition, adding that it must be combined with other ways to reduce emissions and balanced with the need for reliable and affordable energy.

Rob Jackson, head of the Global Carbon Project, a group of scientists who monitor greenhouse gas emissions, praised the study for its cautionary perspective. And though he’s optimistic that carbon capture technology itself will work, he believes very little will ever be stored “because I don’t think we’re willing to pay for it.”

“If we aren’t willing to cut emissions today, why do we expect that people in the future will just automatically pay to remove our pollution?” Jackson said. “We’re just continuing to pollute and not addressing the root of the problem.”

How it works

Carbon dioxide, a gas produced by burning fossil fuels, traps heat close to the ground when released to the atmosphere, where it persists for hundreds of years and raises global temperatures.

Industries and power plants can install equipment to separate carbon dioxide from other gases before it leaves the smokestack, or it can be captured directly from the atmosphere using giant vacuums.

Captured carbon is compressed and shipped to a location where it can be injected deep underground for long-term storage in deep saline or basalt formations and unmineable coal seams — though about three-fourths is pumped back into oil fields to build pressure to help extract more oil.

In the U.S., such projects have faced criticism from some conservatives, who say it is expensive and unnecessary, and from environmentalists, who say it has consistently failed to capture as much pollution as promised and is simply a way for producers of fossil fuels like oil, gas and coal to continue their use.

The most commonly used technology allows facilities to capture and store around 60% of their carbon dioxide emissions during the production process. Anything above that rate is much more difficult and expensive, according to the International Energy Agency.

Gidden, the lead author, said it’s clear that scaling up carbon storage will be important to achieving net-zero emissions and to eventually reduce them, and said the use of basalt formations is promising. But the world cannot wait for that to happen before acting decisively to slash fossil fuel emissions.

“If we prolong our dependence on fossil fuels for too long with the expectation that we will offset that by simply storing carbon underground, we’re likely saddling future generations with a nearly impossible task of dealing with not only our mess, but limited ways of cleaning it up,” he said.

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