Credit: National Academies of Sciences, Engineering and Medicine
To achieve goals for avoiding dangerous climatic change while preserving economic growth, “negative emissions technologies” that remove and sequester carbon dioxide from the air will need to play a significant role in mitigating climate change, according to a new report from the National Academies of Sciences, Engineering, and Medicine.
The report, which urges a substantial research initiative to advance such technologies posthaste, is co-authored by Colorado State University’s Keith Paustian, University Distinguished Professor in the Department of Soil and Crop Sciences and Senior Research Scientist in the Natural Resource Ecology Laboratory. Paustian was tapped to serve on a 17-member national committee whose goal was to develop a research agenda and recommended actions for effective carbon dioxide removal and reliable sequestration methods.
Over the last 18 months, Paustian served as a lead author of the committee report’s section on terrestrial carbon removal – its state of the art, future implications, and recommended research priorities.
Although climate mitigation remains the motivation for global investments in negative emissions technologies, the committee determined that advances in such technologies also could have economic rewards. These could take the form of intellectual property rights and economic benefits that will likely accrue to the nations that develop the best solutions.
“Negative emissions technologies are essential to offset carbon dioxide emissions that would be difficult to eliminate and should be viewed as a component of the climate change mitigation portfolio,” said committee chair Stephen Pacala, the Frederick D. Petrie Professor in Ecology and Evolutionary Biology at Princeton University. “Most climate mitigation efforts are intended to decrease the rate at which people add carbon from fossil fuel reservoirs to the atmosphere. We focused on the reverse – technologies that take carbon out of the air and put it back into ecosystems and into geologic storage.”
Unlike carbon capture and storage technologies that remove carbon dioxide emissions directly from large point sources such as coal power plants, negative emissions technologies remove carbon dioxide (the most important greenhouse gas that causes climate change) directly from the atmosphere, or enhance natural carbon sinks.
The committee concluded that technologies available today can be safely scaled up to capture and store a significant fraction of the total emissions both in the U.S. and globally, but not enough to keep total global warming below two degrees Celsius, the target of the Paris Agreement. Therefore, a concerted research effort is needed to address the constraints that limit deployment of such technologies, such as high costs, land and environmental constraints, and energy requirements.
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In the report, Paustian described the state of the art and challenges of terrestrial carbon sequestration, or removing carbon dioxide from the atmosphere by accelerating carbon storage in soil, plants and wood biomass.
The chapter describes land use and management practices within forests and agricultural lands that increase the total inventory of carbon in the terrestrial biosphere, acting as a “carbon sink” for atmospheric warming. These include:
- Management methods on croplands or pastures, such as reduced tillage or the planting cover crops that increase the total amount of organic carbon contained in agricultural soils
- Planting forest on lands that used to be forest, but were converted to another use (reforestation), or planting forest on lands that were originally grasslands or shrublands (afforestation)
- Forest management practices that increase the amount of carbon per unit land area on existing forest, such as accelerating regeneration after disturbance or lengthening harvest rotations
“The important thing to understand about the terrestrial system is that it’s probably where we can do the most effective early actions that are not so expensive,” Paustian said. “Particularly with respect to the soil, we could also have a lot of other side or co-benefits. These include improved soil health and soil fertility.”
Paustian is an expert in modeling, field measurement and development of assessment tools for soil carbon sequestration and greenhouse gas emissions. In 2006, he served as coordinating lead author for the Intergovernmental Panel on Climate Change’s National Greenhouse Gas Inventory Methods, and also co-authored a previous National Academies report on land use and greenhouse gases.
Technologies ready for scale-up
According to the Oct. 24 report, reforestation, changes in forest management, and changes in agricultural practices that enhance soil carbon storage offer the most immediate promise for climate mitigation, and thus could be ready for large-scale deployment within the next decade, with appropriate policy incentives, governance structures and monitoring systems.
Another technology ripe for scale-up is “bioenergy with carbon capture and sequestration” or BECCS – in which plants or plant-based materials are used to produce electricity, liquid fuels, and/or heat, and any carbon dioxide that is produced is captured and sequestered. However, BECCS and afforestation/reforestation cannot yet provide enough carbon removal at reasonable cost without substantial unintended harm, the report says. Repurposing a significant amount of current agricultural land for growing new forests or feedstocks for bioenergy with carbon capture and sequestration could have significant effects on food availability.
“All the different technologies we covered in the report have tradeoffs, whether those are economic tradeoffs, land availability tradeoffs, or other environmental tradeoffs.”
Two other negative emissions technologies could be revolutionary, the committee said, because they have high potential capacity to remove carbon. One, direct air capture, employs chemical processes to capture carbon dioxide from the air, concentrate it, and inject it into a geologic storage reservoir. However, it is currently limited by high cost. There is no commercial driving force for developing direct air capture technologies; therefore, developing a low-cost option will require sustained government investment.
The committee also examined coastal ‘blue’ carbon, which involves changing land use and management practices to increase carbon stored in living plants or sediments in coastal ecosystems such as tidal marshlands. Although it has a relatively low potential capacity for removing carbon, the committee concluded that coastal blue carbon warrants continued exploration and support.
The committee concluded that negative emissions technologies have not yet received adequate public investment despite expectations that they might provide approximately 30 percent of the net emissions reductions this century.
The study was sponsored by the U.S. Department of Energy, National Oceanic and Atmospheric Administration, Environmental Protection Agency, United States Geological Survey, V. Kann Rasmussen Foundation, Linden Trust for Conservation, and Incite Labs, with support from the National Academy of Sciences’ Arthur L. Day Fund. The National Academies of Sciences, Engineering, and Medicine are private, nonprofit institutions that provide independent, objective analysis and advice to the nation to solve complex problems and inform public policy decisions related to science, technology, and medicine. The National Academies operate under an 1863 congressional charter to the National Academy of Sciences, signed by President Lincoln. For more information, visit http://national-academies.org.