To achieve goals for climate and economic growth, negative-emissions technologies (NETs) that remove and sequester carbon dioxide from the air will need to play a significant role in mitigating climate change, says a new report from the National Academies of Sciences, Engineering, and Medicine. The report calls for the launch of a substantial research initiative to advance these technologies as soon as possible. Although climate mitigation remains the motivation for global investments in NETs, the committee that carried out the study and wrote the report determined that advances in NETs also could have economic rewards, as intellectual property rights and economic benefits likely will accrue to the nations that develop the best technology.
“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 Stephen Pacala, the Frederick D. Petrie Professor in Ecology and Evolutionary Biology at Princeton University and chairman of the committee. “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 the land. We determined that a substantial research initiative should be launched to advance these promising technologies as soon as possible.”
Unlike carbon capture and storage technologies that remove carbon dioxide emissions directly from large point sources such as coal power plants, NETs remove carbon dioxide (the most important greenhouse gas that causes climate change) directly from the atmosphere or enhance natural carbon sinks. Storing the carbon dioxide from NETs has the same impact on the atmosphere and climate as simultaneously preventing an equal amount of carbon dioxide from being emitted. For example, combustion of a gallon of gasoline releases approximately 10 kg of carbon dioxide in the atmosphere. Capturing 10 kg of carbon dioxide from the atmosphere and permanently sequestering it using a NET has the same effect on atmospheric carbon dioxide as any mitigation method that simultaneously prevents a gallon of gasoline combustion.
The committee concluded that the NETs available today could be safely scaled up to capture and store a significant fraction of the total emissions both in the US and globally but not enough to keep total global warming below 2°C, the target of the Paris agreement. Therefore, a concerted research effort is needed to address the constraints that currently limit deployment of NETs, such as high costs, land and environmental constraints, and energy requirements.
Four land-based negative emissions technologies are ready for large-scale deployment at costs competitive with emissions mitigation strategies, the report says. These technologies include reforestation, changes in forest management, and changes in agricultural practices that enhance soil carbon storage. The fourth NET ready for scale up is bioenergy with carbon capture and sequestration—in which plants or plant-based materials are used to produce electricity, liquid fuels, or heat and any carbon dioxide that is produced is captured and sequestered.
However, these four NETs 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. Repurposing tropical forest would harm biodiversity. Research could identify ways to soften the land constraint, for instance, by developing crop plants that take up and sequester carbon more efficiently in soils or by reducing food waste or demand for meat.
Two other negative emissions technologies could be revolutionary, the committee said, because they have high potential capacity to remove carbon. Direct air capture uses chemical processes to capture carbon dioxide from the air, concentrate it, and inject it into a 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. Carbon mineralization—which essentially accelerates weathering so carbon dioxide from the atmosphere forms a chemical bond with reactive minerals—is currently limited by lack of fundamental understanding.
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