Fixing the Global Greenhouse
Getting carbon dioxide out of the sky
THE MOONSHOT Since the Industrial Revolution began in the mid-18th century, the amount of carbon dioxide in the atmosphere has risen more than 35% and the average global temperature has risen by 0.8 degrees Celsius. To avert global warming beyond the 1.5° C target of the 2016 Paris Agreement on climate change, nations must aggressively reduce emissions with a goal toward a net-zero-emission status. Getting there will require collecting, storing, and potentially reusing the extracted carbon as a chemical feedstock. Also central to this effort are still-to-come negative-emission technologies, which by 2050 would, if successful, annually remove as much as 10 billion tons (gigatons) of CO2 from the atmosphere, about a quarter of today’s current yearly emissions. Under consideration are land-intensive negative-emission techniques, such as growing billions of trees and large-scale, plant-based biofuel production, as well as chemical approaches that remove CO2 from the atmosphere and then store the carbon or reuse it to make fuels and other useful products. The goal of removing massive amounts of carbon from the atmosphere is ambitious, but it’s achievable with sufficiently aggressive research, development, and deployment.
THE PHILANTHROPY OPPORTUNITY Philanthropy can accelerate the arrival of carbon dioxide removal technologies as they progress from basic science to engineering to prototype testing to commercial implementation. Valuable interim innovations are already well in development within the context of carbon-neutral energy production. For example, some companies have begun using atmospheric carbon to make fuels. When burned, these fuels recycle the CO2 consumed by their production back into the sky rather than adding more greenhouse gas to the atmosphere. Free from the profit motive, philanthropic initiatives could speed progress from society’s record-high carbon-emitting status to a carbon-neutral state and onward to a negative-emission era. Although climate-related funding totals less than 2% of all philanthropy, targeted investments could create new momentum, institutions, and incentives for more corporate investment in CO2 reduction at the vast scale the world needs.
When Christoph Gebald and Jan Wurzbacher were graduate students a decade ago at ETH Zurich, the Swiss technical university, they made a pact that they would build a company together before they graduated. Little did they know that a decade later their technology would be viewed by world policymakers as a potential savior of the global climate. Their ambitions were far more humble. Like many, they were alarmed about the buildup of carbon dioxide (CO2) and other greenhouse gases in the atmosphere. So when they launched their firm in 2009, their goal, Gebald recalls, was to create technologies that would extract CO2 from the atmosphere and use it as an industrial feedstock. The initial strategy was to create carbon-neutral fuels whose production and use, unlike fossil fuels, would not contribute additional carbon to the atmosphere. Almost as an afterthought in their first business plan, the pair mentioned a more audacious idea: going beyond carbon-neutral technology by actively removing greenhouse gases in ways that would begin to reverse the 250-year atmospheric buildup of CO2, an ability they imagined “wouldn’t be a factor [until] 2050,” says Gebald.
A decade later, what started as an entrepreneurial glimmer in Gebald’s and Wurzbacher’s eyes, has become a company: Climeworks. It has secured a handful of key patents, attracted more than $50 million in private investment and grants, and grown into a company based in Zurich with more than 70 employees. Fuels were just the start. The firm now has partners in agriculture, beverages, and the power industry. What’s more, their technology sucks CO2 right out of the sky, after which the carbon is available for reuse or storage
In the years since the launch of the startup, the concept of Carbon Dioxide Removal (CDR) has gone from a nice-to-have vision to a must-have priority in the multinational environmental community. CDR has been endorsed by the U.S. National Academies and the Intergovernmental Panel on Climate Change (IPCC) as a key to the climate fight. A recent IPCC report stated that all scenarios that allow global warming to remain under the 1.5° C target require massive deployment of CDR.
Climeworks is not alone in the nascent carbon-removal space. Among their competitors is Carbon Engineering, in Squamish, Canada, which is partnering with Chevron and Occidental Petroleum Corporation to build a plant in west Texas that will extract nearly a million tons of CO2 out of the sky each year, storing it in supercritical form (a dense but still fluid physical state) deep underground. “We offer a service to bury CO2 permanently,” says CEO Steve Oldham. Another player, the New York City-based Global Thermostat, is working with ExxonMobil and several U.S. Department of Energy labs to develop its own CDR technologies. As the CDR space expands, others are exploring a wide a diversity of solutions variously based on trees, algae, or concrete.
“We are now well equipped to move past debating ‘why carbon removal’ to ask ‘how can we achieve carbon removal at scale before midcentury?’” according to ClimateWorks, an influential grantmaker. “The market is asking for it much much faster than we thought,” says Gebald.
An Exercise in Gigatons
This new demand for CDR is due to a combination of deep societal concern about global warming and the profit motive. The carbon story has grown more dire as the world economy has expanded: Every year the level of CO2 in the atmosphere increases, setting an-ever rising annual record. This year, that level reached 415 parts per million. That’s up from about 280 parts per million in the mid-18th century, the dawn of the Industrial Revolution, when humankind began using the sky as a dump for its carbon dioxide pollution.
“Our release of fossil-fuel carbon into Earth’s atmosphere in the form of CO2 will be recorded in the rock record as a major planet-wide event, marked by transgressions of shorelines, extinctions of biota, and perturbations of major biogeochemical cycles,” the authors of a 2015 report by the National Academies of Science, Engineering and Medicine wrote.
Healing this planetary disruption will take, for starters, an honest appraisal of the global CO2-budgeting challenge. The numbers just aren’t adding up. Humankind emits roughly 40 billion tons, or gigatons, of CO2 each year. Natural sinks for the carbon — primarily oceans, forests and soils — absorb about half of that amount. The rest of those gigatons are what drives global warming. A modeling study published in Nature Communications in 2015 explored how negative CO2 emissions could help maintain global warming below a 2°C rise above preindustrial values. That’s the Paris Agreement fallback target, lest humanity fails to meet the safer 1.5°C target. The modelers found that depending on future energy and emissions trends between now and 2100, negative emissions of between 0.5 and 11 gigatons of CO2 per year would be required to meet the fallback goal.
Here’s how that would work: Eighty percent of global emissions are created by big, tangible facilities such as industrial plants, refineries, and buildings. It won’t be easy to swap the fossil-fuel diet of these facilities with a renewables diet, or capture carbon from them on large scales, but these actions are doable and already are getting underway. Even so, says Carbon Engineering’s Oldham, “we’re going to run out of flue stacks” that can be filtered of their CO2 pollution. That will leave the remaining and harder-to-get 20% of CO2 emissions to capture from its widely distributed sources: hundreds of millions of tiny carbon-polluting machines like cars, planes, generators, and lawnmowers. (Efforts to electrify vehicles and other small emitters are occurring much too slowly to achieve the Paris goals, an analysis by Shell shows. So for now it is looking like CDR technologies are the hope for making up the shortfall.)
“We are now well equipped to move past debating ‘why carbon removal’ to ask ‘how can we achieve carbon removal at scale before midcentury?’” — Dan Plechaty, Giana Amador, and Jan Mazurek (ClimateWorks report)
For years, the climate policy community avoided talking seriously about carbon dioxide removal. The idea of negative emissions was viewed as a distraction from the most important and practical step: Reducing global emissions of carbon dioxide and other greenhouse gases. But there was another concern, this one anchored in human psychology: Discussing ways to remove carbon from the atmosphere could create a moral hazard, inadvertently reducing societal pressure to decarbonize the global energy system. According to a 2018 article in Science, “some researchers fear [negative emissions technologies] offer policymakers a dangerous excuse to drag their feet on climate action in the hopes that future inventions will clean up the mess.” Others have viewed CDR as a worthy component of an overall portfolio of climate-change solutions, but only to be embraced decades from now after dramatic reduction of carbon pollution presumably will be well on its way.
But now the sense of urgency for CDR has reached a fever point. “Today we are standing on the precipice of the biggest battle that humanity ever faced, precisely for the reason that humanity has not done enough,” former Secretary of State John Kerry said recently at an United Nations event on climate. Many prominent voices in climate policy now say that direct removal of CO2 from the atmosphere is a must and should be executed in conjunction with the rapid reduction of carbon pollution. “Humanity keeps procrastinating on mitigation and so it becomes impossible at some point to meet the safe or declared target of limiting temperature increases to 1.5°C to 2°C without negative emissions,” says Stephen Pacala, an energy expert at Princeton University who led a major study on CDR for the National Academies last year.
A Low-Tech Road: Clearing the Air with Trees
Much of the new carbon-reducing focus is on high-tech companies like Climeworks and Carbon Engineering (see below). But low-tech approaches, such as massive tree-growing projects, will likely have an important role to play as well.
The 2018 National Academies report found that restoring forests that once stood, and managing existing ones better, are two of the safest and cheapest options for removing CO2 from the sky. A study published this past July in Science quantified the power of a concerted global effort to expand existing forests. Growing trees to restore ecosystems, the authors argued, is “the most effective solution at our disposal to mitigate climate change.” And as a global strategy, lead author Jean-Francois Bastin of ETH-Zurich told National Geographic, “reforestation can buy us time to cut our carbon emissions.” Using nearly 80,000 satellite photos, the authors discovered that previous efforts to quantify Earth’s reforestation potential had missed vast swaths of land that had once hosted forests and could be coverted back into forestland. Currently 21 million square miles (5.5 billion hectares) of forest exist; the study revealed an additional 12 million square miles (3.2 billion hectares) where trees once stood. A tree-growing campaign of this magnitude would, in a few decades, remove 750 billion tons of CO2 from the atmosphere. That’s equivalent to nearly 20 years’ worth of total global C02 emission at the current annual rate.
More than half of that additional forestation potential lies in just six countries: Russia, the United States, Canada, Australia, Brazil and China. And as the IPCC showed in a recent report on land use, growing trees at this scale could have additional benefits by countering poverty, desertification, and loss of biodiversity.
“Today we are standing on the precipice of the biggest battle that humanity ever faced, precisely for the reason that humanity has not done enough.” — former Secretary of State John Kerry
But the tree solution faces serious obstacles. Rising temperatures make it harder, physiologically, for trees to grow and that means time to deploy this solution could be running out. “We have a narrow window of time in which to restore global tree cover,” wrote Robin Chazdon and Pedro Brancalion in a commentary on the July Science paper. Global warming also has fueled a rise in wildfires, which emit huge amounts of CO2 into the atmosphere. What’s more, forests can be cut down or deliberately burned; they’re susceptible to poor management by governments. The pro-deforestation policies by Brazilian president Jair Bolsonaro contributed to the more than 60,000 fires that torched the Amazon this past summer. Catalyzed by unusually warm temperatures, the fires blazed from Siberia to Canada to Europe, underscoring the potential challenges and pitfalls of relying on forests to fight global climate change.
Trees seem inherently benevolent, but efforts to promote their planting could have unintended and harmful consequences. Incentivizing forest growth could create competition for land currently used for food production. The 2018 National Academies report said such competition “might have a significant effect on food availability and food prices, with far-reaching effects on national security and biodiversity.” To be sure, humanity should grow billions of new trees. But relying on trees and other plants to absorb all of our carbon pollution poses big risks.
The High-Tech Road: Clearing the air with chemistry
What if we could use new chemical approaches and machines to dramatically lighten the atmosphere’s carbon load? One of the leading CDR techniques is known as direct air capture (DAC). By way of clever chemistry, DAC devices scrub CO2 directly from the atmosphere, building on techniques used for decades to clean the air in submarines and space capsules. Capturing the carbon is the first step. The second is either permanently storing the carbon in underground reservoirs or using it as a feedstock for making fuel or other chemical products. Theoretically, such industrial processes could, if deployed globally, remove all the CO2 human society annually emits. At the moment, however, the technology is way too expensive for deployment beyond niche markets.
Carbon Engineering is a leader in the DAC business. Its business plan is to build large plants that use liquid solvents to sop up atmospheric carbon dioxide. The technology begins by blowing air from the atmosphere into a solution of lye, a strong base also known as potassium hydroxide. In the resulting reaction, the CO2 in the air is converted to crystalline potassium carbonate (K2CO3). Then, at high temperature, the CO2 captured in the reaction is liberated and goes either into storage as supercritical CO2 or into industrial processes that yield fuel or other chemicals. To generate the 900° C required for the process, Carbon Engineering’s current plant design burns natural gas. But the CO2 produced from that combustion is collected and processed too, so the plant produces true net negative carbon emissions.
Other DAC companies eschew big chemical plants using liquids in favor of modular designs that use relatively small fans to draw air. Their systems are theoretically small enough to be mass produced. Climeworks, the Swiss company, uses devices the size of washing machines to capture CO2. The firm uses a solid filter covered in amine chemicals — derived from ammonia — to react with the carbon. When the filter is subsequently heated, the gas desorbs and can be shunted into tanks or pipes for commercial uses like carbonating beverages and enriching greenhouses, or sent into the ground for permanent storage. Global Thermostat, meanwhile, blows air over amine filters that bond with CO2 to form carbamate molecules, a process that occurs below 100°C. As with Climeworks’ process, the second step is to remove the CO2 for storage or reuse and regenerate the filters for another cycle of CO2 extraction. The company has been refining the technology with the help of a 40-foot-high test facility in Menlo Park, California. In July, Global Thermostat signed its agreement with ExxonMobil so that the energy giant can evaluate the scalability of the technology.
Pitched arguments have raged over how much DAC will eventually cost. A paper published by Carbon Engineering founder David Keith last year estimated that the technology could remove millions of tons of CO2 from the atmosphere at a cost of $94 per ton. The 2018 National Academies report cites a higher estimate based on a plant that uses liquid solvents, at $199 to $357 per ton of CO2 captured, depending on assumptions related to energy costs and thermal requirements. But Princeton biologist Stephen Pacala, who chaired the report, is upbeat that future innovations could prove Keith right. He calculates, based on the emissions caused by fuel burning, that the societal cost for a $100/ton DAC technology could be paid for by a gas tax of roughly $1 per gallon. That could make it an affordable technology, says Pacala, for example to offset emissions from airplanes.
CO2 as a 21st Century Feedstock
The carbon removal technology that’s gotten the most attention from climate scientists is Bio-energy with Carbon Capture and Storage (BECCS). BECCS harnesses the carbon-sucking power of plants, but combines it with chemical engineering to produce chemicals or energy, usually in the form of fuels. BECCS is an umbrella term for the entire field of carbon-negative biopower, whether the goal is to turn corn and sugarcane into biofuels, urban organic waste into gasoline, or farm waste into electrical power.
Nature provides the inspiration for BECCS. As plants grow, the process of photosynthesis, which builds biomass, removes carbon from the atmosphere. BECCS facilities burn or process the biomass to create electricity or biofuels. Or they produce biochar, akin to charcoal, which can be added to soils to promote crop growth. Feedstocks for BECCS vary, ranging from crops grown specifically for burning, like switchgrass, to organic wastes to algae.
Bioenergy with Carbon Capture and Storage (BECCS) is an umbrella term for the entire field of carbon-negative biopower, whether the goal is to turn corn and sugarcane into biofuels, urban organic waste into gasoline, or farm waste into electrical power.
Fossil fuels, as their name indicates, originally derive from ancient carbonaceous material, mostly plants. So it’s not surprising that a technology like BECCS — which is premised on the power of photosynthesis but optimized for the modern energy needs of fuel or electricity — is such a potent idea. How carbon atoms are arranged on a molecule of cellulose, the main polymer in plants, and one of the most abundant natural polymers on the planet, explains the potential of BECCS as a concept. Cellulose polymers are built from chemical components featuring six-carbon rings. During bioenergy reactions, two of those carbon atoms generally come off, forming two CO2 molecules. The rest of the carbon atoms can then form ethanol, the most important biofuel, or other chemicals. If the CO2 produced during the production of cellulose can be sequestered indefinitely, say in underground rock formations, the net result would be net-negative CO2 emissions.
The individual pieces of BECCS technology are each technologically mature. Myriad power plants around the world already burn or process biomass to make fuel. And a number or facilities that inject CO2 into old oil wells to obtain more crude have shown that the carbon can be stored at depth indefinitely. So over the last decade, as the need to rapidly reduce the carbon content in the atmosphere has become clear, the IPCC determined from its climate models that deploying the technology has become crucial to reaching key policy goals — like the 1.5°C target of the Paris agreement. A major review of BECCS in 2015 found that the technique could be scaled to annually produce 100 exojoules of energy, about half the energy currently produced by burning fossil fuels. And models developed by the International Energy Agency suggest that BECCS could remove 2 billion tons of CO2 each year by 2050 to keep global temperature rise below 2° C.
But while BECCS is a leader on paper, the challenge is putting each of its elements together in the real world. That’s never been tried at the scale required even for a single major power plant. The biggest question is how much land the approach will require. To annually remove from the atmosphere a single gigaton–a tenth of the negative emissions needed to avert the 2-degree limit — farmers would have to grow BECCS feedstock on 30 to 43 million hectares. Removing all 10 gigatons of CO2 using BECCS would require “almost 40 percent of global cropland,” pointed out the 2018 National Academies report.
Pacala is more blunt. It’s already hard for countries to support a global food system while also providing habitat for rapidly plummeting global biodiversity, he says. As Earth’s population rises, demand for food is forecasted to double. Adding a major new demand — growing crops for carbon-negative energy — could break the system. “There simply isn’t enough arable land,” he says.
That’s not to say that the technology won’t be a player in the negative-emissions industry of the future. Niche markets, says Pacala, could offer a home for BECCS, including in the United States, where in 2006 3.6 million hectares were devoted to growing corn and other crops for ethanol fuel for vehicles. As American automobiles electrify, the demand for liquid fuel could diminish. Pacala sees that as an opportunity to convert croplands growing corn for ethanol into cropland for BECCS feedstocks. Fast-growing plants like miscanthus, switchgrass, or poplar would be good feedstocks to start with.
Biochar, which is charcoal produced by heating biomass, is another element of the CDR portfolio. It can be a byproduct of biofuel production or produced by dedicated plants. The United States produces as much as 77,000 tons of the material annually. On farms it provides phosphorus and other nutrients, retains moisture, and softens soils to make planting easier. While there are concerns that biochar in soils could break down and emit carbon over long time spans, a 2010 study in Nature Communications found that a massive global program to produce biochar could reduce the equivalent of 2 gigatons of CO2 emissions annually.
How about using air as a feedstock to build new and useful materials? Using the sky’s carbon to make valuable products often is referred to as carbon dioxide utilization. It relies either on the concentrated streams of carbon collected from power plants or the diffuse streams removed via CDR from the atmosphere itself.
That’s a key element of the Climeworks strategy. The fuels it will soon produce could theoretically power diesel engines, jets, home furnaces, or cars. These fuels would work with the current fossil fuel infrastructure, including its pipelines, gas stations and cars, though they would probably initially be more expensive than the fossil-derived liquid fuels.
In the context of biological conversion processes like BECCS, it is possible to convert CO2 into biofuels, fertilizers, and other chemicals. Here, algae-based technology could become dominant. These cells already undergird large industrial production of biofuels, proteins, food additives, and specialized chemicals. Algae is incredibly efficient. Compared to an acre of farmland growing soybean, canola or corn, algae grown in the equivalent of an acre of seawater contains 50 times more protein. And algae grown with atmospheric CO2 could be used to make products including oil, fish food and plastic.
Storing CO2 by the Gigaton
CDR technologies grab carbon from the air; but over the long term, where that carbon ends up is the important thing. There’s a lot of gas to manage. In addition to using the captured greenhouse gas as a new industrial feedstock, permanent storage of many-gigaton quantities of the gas — most of it deep below bedrock where vast porous rock formations could trap the gas in perpetuity — will have to be a major part of the solution.
Reducing the atmospheric concentration of CO2 by 50 ppm (about 12% of the current concentration), for example, would require a net removal of 400 billion tons of CO2. An influential 2011 study, based on the experience by fossil fuel and waste management industries operating in deep underground formations concluded that 10 times that amount of storage exists globally and would be “practical” to tap. The figure ballooned to 30 times as much when the authors included in their sequestration map sites that would be effective for carbon storage but harder to use. Last year the U.S. injected 61 million tons, or megatons, of CO2 for permanent underground storage. Relative to the many-gigaton scope of the problem, that’s not a lot, but it does confirm that some of the requisite technical know-how is in hand.
Recent geological research has shown the promise of injecting CO2 into deep basalt formations, where it chemically transforms into carbonate rock. Meanwhile, old oil wells are also getting new attention. For more than 50 years, the oil industry has injected CO2 underground as part of its efforts to eke more crude from poorly performing old fields. Enhanced Oil Recovery (EOR) involves pumping pressurized CO2 deep into an oil formation, creating pressure that forces previously recalcitrant oil up other holes called production wells. But some of the carbon that is injected underground during EOR stays there, more or less permanently. That’s why, on average, EOR leads to petroleum production with a net carbon footprint that is 37% lower than petroleum produced from a fresh well, the International Energy Agency estimates.
Turning CO2 into carbonate rock is the newest part of the storage vision. The most-well understood element of carbon storage is the vast number of underground formations of deep, porous sedimentary rocks, which are often filled with saline. To store CO2 underground, companies first compress the gas until it reaches a supercritical state that combines traits of liquid and gaseous phases. The carbon is then injected into the formations, including sandstone or limestone layers. Usually above those strata is a layer known as a seal layer, composed of an impermeable rock, for example like shale. Leaks to the surface occur only if there’s a fracture. According to the 2019 National Academies report, “Sequestration of supercritical CO2 in the pore spaces of sedimentary rocks is the most mature of the options available today for reliable storage.”
Globally, geologists estimate that there’s enough storage capacity to sequester as much as 25 trillion tons of carbon dioxide. That’s roughly twenty five times more than the trillion tons that the IPCC says must be captured from the atmosphere by 2100 to keep global warming under 1.5°C. Beginning in the summer of 2019, Climeworks began offering carbon sequestration as a paid service: For €7 per month, or about $8, the firm will permanently store 85 kg (187 lbs) of CO2 underground at a facility in Iceland. The company says thousands of customers have contacted it about the service. A tiny start, but a start.
The Philanthropy Connection
There is no guarantee humanity will make the technological, societal, and political leaps necessary to manage our carbon crisis. Certain, however, is it will take many billions of dollars to even begin chipping away at the challenge. Most R&D funding for CDR has come thus far from governments or the private sector. A policy paper by ClimateWorks lays out ways that philanthropists could speed the development of negative emissions. “Constituting less than two percent of all philanthropy, we don’t imagine climate grants alone will get us to scale but we can help create better rules and tools to attract the patient capital and private investment needed to get the job done,” wrote program manager Dan Plechaty and two co-authors. In 2018, for example, ClimateWorks gave five grants totaling $873,000 to advance carbon dioxide removal. That’s a pittance compared to the scale of the problem and the stakes involved. Philanthropies spend roughly $500 million per year on climate change. According to Noah Deich, executive director for Carbon 180, a climate-focused nongovernmental organization in in Oakland, California. “We need to increase the pie and expand the fraction of that pie that goes to carbon removal if you want to move the needle.”
“We can follow the solar energy playbook for technologies like air capture.” — Noah Deich, Executive Director of Carbon180
Driving public policy to encourage the growth of carbon removal could be an important role for philanthropy. The nonprofit sector can also advocate for R&D dollars and create ways to promote the research enterprise. “There’s only about 200 people in the world working on air capture,” says Carbon Enginnering’s Oldham. “There needs to be more.”
Deich draws inspiration from government efforts that began in the 1970’s to drive the development of the solar energy industry. These included research funding, tax credits for deployment of solar panels, and procurement of solar energy for government projects. “We can follow the solar energy playbook for technologies like air capture,” says Deich. Funders have at their disposal major studies on how a carbon-negative research agenda might look. One by the World Resources Institute outlines a proposed annual $325 million research and development budget covering biomass studies, research on air-capture machines, genetically modified plants with enhanced carbon uptake, and monitoring of soils and underground reservoirs to assess their reliability for long-term storage.
Meanwhile, policymakers have created some rules that take the first steps toward encouraging carbon dioxide removal. The nonprofit sector could help maintain and strengthen that nascent policy infrastructure. In 2018, Congress passed a provision dubbed “45Q” that provides a $10 tax credit for every ton of CO2 captured by an industrial facility that would have otherwise emitted the pollution. The credit is set to increase to $35/ton by 2024. Even so, according to the Energy Information Administration, these tax credits “do not appear large enough to encourage substantial market penetration” in the U.S. power sector, suggesting that such policies must be honed or strengthened. New tax credits could specifically target atmospheric carbon removal, for example by stipulating that 1% of cement used in new construction would have to be produced with carbon-sequestering technologies.
The surging development of the renewable energy sector has its roots in policies that took 50 years to deliver. But the time it took for that revolution to gain momentum has put humanity in a serious carbon crunch. Now the need for another renaissance, this one in carbon-negative tech, is much more urgent. “We don’t have that luxury of spending the next half-century figuring out these technologies,” says Deich. Oldham says debating responses to an overwhelming problem like climate change shouldn’t be about pitting traditional ways to mitigate emissions against newer CDR approaches. “We need all of the above,” he says.
Eli Kintisch is a freelance correspondent for Science magazine and video producer in Washington, D.C.
