Zero-carbon technologies won't be enough to avert climate change, former Energy Secretary Ernest Moniz said last week. We're going to need negative-carbon technologies, too. But those appear to be a long-way off.
"I think it's going to be a long time before we get to that place of scrubbing the atmosphere," he said Thursday in an address to the American Academy for the Advancement of Science.
Meanwhile, much of the scrubbing is left to plants. Mangrove forests, for example, are capable of storing much more carbon than rainforests do, scientists have found, if only humans would stop de-foresting mangroves and start re-foresting them. Even then, there are plants that some humans think could sequester carbon even more efficiently than they do naturally.
"I don’t mean just trees, but genetic modification of plants to fix more carbon and the like," Moniz said. "There’s a whole palette here to be explored, and right now certainly the federal R&D budget in this area is very, very minimal."
For example, grasses could be engineered to grow deeper roots. The carbon they draw from the atmosphere would be stored in those roots deep underground and would be less likely to return to the atmosphere when the grasses decompose or the soil is disturbed.
Biological carbon sequestration has some advantages over inorganic methods:
"Today, there’s a lot of argument, but certainly it’s not crazy to say that capturing CO2 out of the atmosphere—which is very very low density, we said 410 parts per million—is very, very expensive, like $1,000 a ton," Moniz said. "We’ve got to get that cost way down through innovation. But secondly we also haven’t quite figured out what we do if we captured hundreds of gigatons. We’ve got to do something with it."
Ideally, captured CO2 could serve as a building block for a low-carbon or no-carbon fuel. It could be made into products, such as building materials, cements, chemicals, plastics, grid batteries, media for enhanced oil recovery, solar fuels. But the massive amount of CO2 that people have to capture—one gigaton, or one billion metric tons, each year—means much of it may have to be stored underground.
"I think it’s unclear to what extent it's socially acceptable to be putting these huge amounts of CO2 underground, and that itself will have different political ramifications in different parts of the country."
Plants already circulate 44o times that much atmospheric carbon, but they sequester only 2 to 3 percent of what they circulate. The rest returns to the atmosphere.
One of Moniz's last acts as energy secretary was to receive a final report from his Secretary of Energy Advisory Board that extolls the virtues of biological carbon sequestration. It poses the following questions:
"Could this natural biological carbon cycle be harnessed to absorb more carbon from the atmosphere, store more carbon on land, or use a combination of both to produce negative emissions? Could this be achieved as a positive co-benefit of increasing productivity of crops for food, bioenergy, feed and fiber that the world will need, and thereby be of commercial value?"
The report calls for federal support for research to:
a) Increase the photosynthetic efficiency and optimize crops for food, bioenergy, feed, and fiber, as well as trees used for bioenergy, reforestation and afforestation, with no marginal increase in resource inputs, such as fresh water, fertilizers, and pesticides, and preferably with reductions in each of these.
b) Rigorously evaluate the benefits and limitations of marine macro algae as ab ioenergy feedstock for both land-based energy… as well as for liquid transportation fuels.
c) Identify approaches to reduce decomposition of soil organic carbonand N2O emission impact by taking into account the biology and chemistry of soil carbon decay. Examples include creating roots that go deeper in the rhizosphere with higher lignin content.
d) Optimize crops and management technology that stabilize organic carbon over longer time frames including accelerating the transition to no-till agriculture, sustaining no-till land after the transition is made and extending the period in which forests are net CO2 sinks.
e) Because of the complexity of the biosphere, intensify research in understanding the ecological impact of harnessing the natural biological carbon cycle, including using systems modeling to understand the net global carbon impact.
"We're very very supportive of that," said Moniz, who now heads the Energy Futures Initiative, an organization that seeks to provide governments with "analytically-based, unbiased policy options." EFI, Moniz said, sees "huge opportunities in the biological sphere."
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