Can carbon dioxide removal save the planet?

Imagine 10 million car-sized contraptions dotted along shorelines and scattered throughout open spaces, sucking carbon dioxide from the air, powered by vast amounts of electricity and water. Or immense complexes for pulverizing and dumping limestone into the oceans at rates near the current use of coal. Or arable land devoted to growing biofuel rather than food on a planet with 9 billion people to feed.

The failure to reduce greenhouse-gas emissions will likely require countries to organize such massive efforts — called carbon-dioxide removal (CDR) techniques — or face temperatures rising more than the 3.6 degrees Fahrenheit above pre-industrial levels, which scientists and the majority of nations have agreed is the threshold for avoiding crippling heat waves and droughts, severe storms and floods, and increases in sea level.

A United Nations Intergovernmental Panel on Climate Change (IPCC) executive summary report suggests that if the world overshoots the acceptable temperature increase, getting back on track will require deploying “CDR technologies to an extent that net global carbon dioxide emissions become negative” before 2100, according to Reuters, which reported on a leaked draft of the summary in January.

The idea of “negative emissions” implies removing more greenhouse gases from the atmosphere than are emitted into it in order to lower the overall concentration of CO2. Last year concentration levels reached 400 parts per million of CO2 for the first time in millions of years, while some climate scientists have argued it was unsafe to surpass even 350 ppm. Nonetheless the world has been unable to stem the rise in its greenhouse-gas emissions, let alone develop a way to remove or eliminate more than 100 percent of them. The global mean temperature has already increased by 1.4 degrees Fahrenheit since the Industrial Revolution.

The official IPCC report is due out in mid-April and will be the third and final part of its fifth assessment of the planet’s climate problem. The last assessment came out in 2007.

CDR is a blanket term for umpteen potential approaches to extracting CO2 from the atmosphere. They range from planting forests and creating biochar to spurring more algae growth in the ocean and chemically pulling CO2 from the air. Many of the strategies have been discussed for years, but almost none have been used on a large, organized scale, leaving their potential theoretical. There are no U.S. government agencies or national laboratories with research programs devoted to furthering CDR, and only a handful of universities are looking into it. By all accounts, the strategies that the IPCC suggests are essential to preventing dangerous levels of climate change are poorly understood and undeveloped.

“There’s really no reason to believe they [CDR technologies] can be applied on that [a global] scale,” says Tim Kruger, founder and program manager for the University of Oxford’s Geoengineering Programme.

The challenges to developing and adopting CDR appear to be monumental.  Any CDR effort that could meaningfully lower the concentration of CO2 in the atmosphere by the end of the century would have to be deployed on a massive scale.  Such a large endeavor would have byproducts (including indefinitely storing CO2, in some instances) and drawbacks to contend with.  And the cost of a massive undertaking, while highly speculative, would require substantial funds from many nations sustained over decades. Just drumming up the research money to study the technical feasibility of each technique, let alone its governance, biodiversity and agricultural implications has proved challenging.

“We need to understand what the costs and the side effects of these techniques are to understand if they’re deployable and to what level they’d be deployable,” says Kruger. “If you can use them, that influences policy. If you can’t use them, we should recognize that the scenarios that include them are not valid.” 

Holistically assessing the impact of CDR is one challenge, but research and economic questions also remain about many of the ideas. When it comes to biologically based techniques, such as growing biofuels and storing CO2 associated with its production underground, there are concerns about the amount of land that would be needed. Approaches that decrease the ocean’s acidity by adding limestone or other minerals to it so that it absorbs more CO2 would require infrastructure rivaling that employed by the coal industry. Pulling CO2 directly from the air entails a huge amount of energy.

“There are reasons to go on researching in all these areas,” says Duncan McLaren, a U.K.-based environmental consultant specializing in geoengineering, “but on balance it would seem the most sustainable option would be to look for direct air capture that could be powered through renewables.”

Many agree with him, and the notion of using chemical processes to pull CO2 from ambient air — also known as direct air capture (DAC) — has received significant attention in the past decade. The CO2 collection units could be located anywhere in the world, and manufacturing enough of the units to impact climate change is conceivable.

Within the last decade four small, private companies, most with academic scientists behind them, have attempted to commercialize DAC by trying to sell the CO2 they extract from the air, which would then be used for enhanced oil recovery, in carbonated beverages and to support growth in greenhouses, among other ideas.

While these applications don’t address climate change, they presumably allow researchers to make a profit selling CO2, which will finance further research into DAC. But so far none of the companies have moved beyond the pilot-project stage.

“Essentially, putting it in a horrible way, they’re in the valley of death,” says McLaren, referring to Silicon Valley’s term for new ideas without proven profitability. Demonstrating that a novel technology can make money typically requires funders who are willing to risk their investment — a hard breed to come by.

Technologies that remove CO2 from the air are already used in submarines and spaceflight, but commercially replicating the idea for a larger market, let alone on a scale that would impact climate change and be affordable, has yet to be accomplished.

“I deep down see this as an economics problem,” says Klaus Lackner, director of the Lenfest Center for Sustainable Energy at Columbia University’s Earth Institute.

Lackner first proposed CO2 removal as a response to climate change in 1999, suggesting that a particular plastic resin he and his colleagues discovered could pull CO2 from the air 1,000 times faster than a tree. Ambient air would pass through a line of collector units, each the size of a standard shipping container. Once the resin had absorbed the CO2, it would be released from the resin with water as a pure stream of CO2. It would then need to be stored underground indefinitely or turned into a salt for disposal.

“If you could make it into a salt, that would be the dream, I think, of everybody,” says Paul Falkowski, a Rutgers University biological oceanographer and member of the National Academy of Sciences group examining geoengineering. But so far aspects of changing CO2 into a carbonate — calcium carbonate, magnesium carbonate or sodium bicarbonate (baking powder) — at a large scale have proved too difficult to overcome. 

Disposal of the CO2 aside, each of the dozen or so ideas for extracting the gas from the air must take into account concerns over excessive energy or water use, and all struggle with the cost.

A 2011 American Physical Society (APS) report assessing the current state of DAC technology, headed by Robert Socolow, who co-leads Princeton’s Carbon Mitigation Initiative, damningly concluded that to remove a metric ton of CO2 from the atmosphere using DAC would cost more than $600.  Given that a single large coal plant emits roughly 6 million metric tons of CO2 annually, a $600 price tag is unthinkable.

Those devoted to developing DAC were swift to rebut the report’s conclusions. Harvard Professor David Keith, a proponent of solar-radiation management and founder of the DAC company Carbon Engineering, has said the cost will be lower than $250 per metric ton.

Lackner has proposed that over time the price could go as low as $30 a ton. “Any new process is very expensive,” he says of the APS report, adding that it analyzed a single approach to DAC. “Their statement is a little bit like studying aerodynamics in a penguin and proving that it cannot fly. I agree with that, and I can’t stand here and say that you are wrong, because you are right. I think the mistake is in the generalization.”

In fact Roger Aines a senior scientist at Lawrence Livermore Laboratory and contributor to the 2011 DAC report concurs in part.

“[The] report had a very chilling effect on this field. It wasn’t our intent, but it was the way the answer came out,” says Aines. “I hate to say that we really squashed any further funding in the area, but we probably did.”

Aines is quick to agree that the cost of DAC can be driven down, but says, “It comes back to the gigaton problem. If you wanted to remove a gigaton of CO2 from the atmosphere right now and you had David [Keith’s] process at $250 ton or putting carbon capture on coal-fired power plants at let’s say $100 a ton, the choice is clear.” 

The country’s national laboratories are not focused on researching DAC, says Aines, but rather on capturing CO2 produced at power plants. While most agree that line of research is essential, it doesn’t remove existing CO2 from the atmosphere; it only prevents us from adding more. Advancing those power plant technologies ultimately adds to the understanding of DAC, says Aines. “It’s not the time to apply [DAC] on a large scale; it’s time to do the research.”

But therein lies the rub: Research requires funding, and according to Lackner, scientists need the money now. He concluded a recent paper on DAC with the comment “Given the enormity of the global climate challenge, we think this R&D needs to be scaled up urgently.”

For Aines’ part, he’s optimistic about the possible impact of the new IPCC report: “It’s going to encourage that long-term research in a very productive way.”