Researchers released a peer-reviewed analysis in the academic journal Climate Policy today arguing that the urgent work of removing excess carbon from the atmosphere — known as carbon dioxide removal (CDR) — can't just rely on complex, untested techniques to capture carbon dioxide (CO2) and inject it deep underground or pump it into the ocean. Rather, they show that nature-based solutions, which include restoring forests and other ecosystems that capture atmospheric CO2 using the ancient biochemical process of photosynthesis and store organic carbon in plants and soil, are also necessary for achieving global climate goals.
"We must rapidly reduce the production of new greenhouse gas emissions worldwide. At the same time, we must also remove and store excess carbon already polluting the atmosphere. In recent years, innovative high-tech CDR companies have introduced promising solutions for capturing carbon. However, these solutions are still in research and development stages, and they are not yet proven at the scale needed," said Charlotte Streck, a professor at the University of Potsdam, the founder of Climate Focus and the lead author of the Climate Policy journal analysis, "Considering durability in carbon dioxide removal strategies for climate change mitigation."
"At the same time, it's well established that forests and other ecosystems are effective at storing carbon — while also providing clean air and water, safeguarding biodiversity and keeping the planet cool. We must embrace both high-tech and natural methods of CDR to succeed," she said.
Countries and companies have embraced CDR, which was written into the Paris climate agreement, as a key strategy for fulfilling their climate goals and net zero commitments. It's estimated that companies will invest some $250 billion in CDR by 2050, most of which will go to high-tech concepts that aren't yet operational.
Nature and tech CDR are often pitted against either. In those comparisons, nature CDR is referred to as "temporary" and tech CDR as "permanent." Such binary classification implies the necessity of giving priority to tech over nature. However, creating such false choice does not help as available CDR strategies are all contributing to climate change mitigation, but differ in their risk profile, short- and long-term benefits. While tech CDR is more durable, nature CDR is tested, can be deployed now and can yield benefits for nature and people.
"Nature-based and engineered CDR can be deployed synergistically, including through investment portfolios that balance the conditions of feasibility, durability, and sustainability," said Matthew Brander, professor of carbon accounting at the University of Edinburgh Business School. "Engineered novel CDR methods offer higher durability and lower reversal risks. However, conventional nature-based CDR methods that rely on storing carbon in vegetation and soil are the most immediately deployable methods at scale, and costs are comparatively low. It's clear that high-tech and natural CDR methods can complement—not compete with—one another."
The authors demonstrate that a balanced, comprehensive approach to investments in all forms of CDR offers the best prospect of meeting the long-term temperature goal of the Paris Agreement in the context of sustainable development.
What is CDR?
The authors of the authoritative Intergovernmental Panel on Climate Change (IPCC) define CDR as human "activities removing carbon dioxide (CO2) from the atmosphere and durably storing it in geological, terrestrial or ocean reservoirs, or in products."
CDR is classified according to how it captures carbon (for example, through photosynthesis or inorganic chemistry); where the carbon is stored (for example, land or sea); and the way in which it is stored, which can include plants and trees, soil, deep underground rock formations, minerals and the ocean floor.
The most successful CDR methods demonstrate readiness, feasibility, and the ability to remove a large amount of carbon without delay; sustainability, including the delivery of social and environmental benefits; and the durability of storage over the long term. Currently, no single CDR technique optimizes all three of these conditions and can sustain them over long periods of time.
"Engineered CDR is extremely expensive and will require huge amounts of cheap renewable energy, along with years of investment in research and development, before it's ready to scale." said Peter Ellis, the global director of natural climate solutions science at The Nature Conservancy. "In contrast, nature-based CDR is cheap and powered by photosynthesis, which has been in research and development in efficient self-replicating prototypes called plants for 3 billion years."
The risk that stored carbon is released back into the atmosphere (e.g., through hazards, fire, pests or logging) is a key consideration in the CDR debate. Plans to store carbon in rocks, for example, are risky early on, before the carbon successfully hardens into minerals (mineralization). Over time, however, the risk of this CDR approach failing is significantly reduced. At the same time, natural approaches to CDR face different types and levels of risk over time. Not all newly planted ecosystems, for example, survive, and, even after these ecosystems are successfully established, they are vulnerable to unexpected human activities or the impacts of climate change, including fire, which releases carbon stored in wood back into the atmosphere.
"Policymakers and investors should encourage a balanced, comprehensive approach to investments in both nature- and tech-based CDR," said Streck. "A balanced portfolio mitigates against risks of any one strategy and is most likely to make meaningful contributions toward achieving Paris Agreement goals."
