Over the last twenty years, the concept of negative emissions, or net removal of carbon from the atmosphere, has moved out of the realm of science fiction and into mainstream discussions about preventing climate change. One solution in particular has swooped onto the scene as a kind of negative emissions super hero: Bioenergy with carbon capture and storage (BECCS).

BECCS means burning biomass for energy, separating CO2 in the process, and then injecting this gas deep underground in a reservoir capped by non-porous rock or mineral. Of the 116 scenarios that the Intergovernmental Panel on Climate Change’s (IPCC) most recent Fifth Assessment Report suggests will stabilize our climate by the end of the century, 101 of them rely on BECCS.

How much BECCS? Across those scenarios, IPCC models suggest we’ll need to remove an average of 616 billion tons of CO2 by the end of the century. To put that amount in some perspective, it’s about two thirds of the world’s current carbon budget (optimistically estimated at over 900 billion tons of CO2), or the amount that we have the luxury of dumping into the air before raising global temperatures by two degrees Celsius, a frightening tipping point for our earth.

As a global society, we’re currently emitting over 40 billion tons of CO2 every year, a rate we can continue for less than twenty years. To keep warming below 1.5 degrees by 2100, as the Paris Agreement states is the goal, we’ll need to stick to a carbon budget that our current emissions rates are likely to blow through in about five years.

Can BECCS save us? A number of critics, climate scientists, and environmental groups have refused to hop on the bioenergy bandwagon. Among other things, the technology has been called a “false solution,” a “moral hazard,” and a “dangerous distraction.” So how has such a contentious solution so thoroughly infiltrated our most internationally trusted climate models? And what’s so risky about a little, or a lot, of bioenergy?


Why Is BECCS So Attractive?

To be fair to the Integrated Assessment Models (IAMs), the interdisciplinary scenario-crunchers that form the backbone of IPCC assessments, assumptions aren’t hidden in the models’ gears. The Fifth Assessment Report spends pages and appendixes detailing assumptions made about international agreements, political will, future energy demand, human behavior, and the costs of different technologies.

Crucially, the models portray BECCS as a cheaper option than making a more full-scale and near-term leap to clean energy. Without carbon capture and storage (CCS) – both the regular and bioenergy kind – the report predicts that the cost of keeping the planet from warming two degrees will more than double, rising by an average of 138 percent.

Why? Because fossils still fuel our economy. Most nationally and internationally respected cost-sensitive forecasts of our energy mix – say forecasts made by the EPA, EIA, and IEA – all suggest that fossil fuels will still supply the bulk of U.S. and world energy in thirty years. As the IEA’s Executive Director, Maria von der Hoeven, has said, “With coal and other fossil fuels remaining dominant in the fuel mix, there is no climate friendly scenario in the long run without CCS.”

CCS solutions allow our current energy infrastructure to remain, in more ways than one. Plain old CCS, which isn’t that old, can prevent a lot of the carbon pollution that results from combusting or processing fossil fuels. The U.S. Environmental Protection Agency (EPA) estimates that CCS technologies can reduce by 80 to 90 percent the carbon footprints of power plants as well as historically polluting industries like cement, steel, paper, and fertilizer production. By dramatically cleansing the emissions of these industries, CCS offers them a lifeline even in a future of high carbon prices.

Adding bioenergy and transforming CCS into a negative emissions technology (NET) makes this solution doubly attractive to predictive models. BECCS promises to both produce energy and suck up the carbon that plants (the green, leafy kind) store during growth. By producing large scale negative emissions BECCS will theoretically increase our carbon budget, buying more time for us to get our political and technological acts together while we transition to cleaner energy sources and infrastructure. As the IPCC suggests, negative emissions become even more attractive under future scenarios that place steep price tags on carbon. In these scenarios, BECCS facilities have the added benefit of getting paid to eat carbon.

Besides its economic allure, BECCS also attracts because the technology’s component parts – the energy production, the capture, and the storage – all work, at least in some demonstrable form. Though a number of pilot projects have failed or collapsed from funding pull-outs, as of this year BECCS fans can nod to the world’s first operational large scale plant. As part of an Arthur Daniels Midland (ADM) ethanol production facility in Decatur, IL, a newly constructed BEECS plant captures CO2 in the process of fermenting corn. The gas is then injected into nearby Mount Simon sandstone. The plant aims to capture and store about 2.26 million metric tons of CO2 over a pilot period of two and a half years.

Despite removing millions of tons of carbon, however, the overall ADM facility remains firmly on the wrong side of carbon neutral. As a recent CarbonBrief piece reports, in 2014 the facility recorded over 5 million metric tons of CO2 equivalent emissions. If we consider those emission numbers a proxy the near future, the facility will still emit about 12.7 million metric tons of CO2 over the time frame of the BECCS project.

The storage side of CCS has been quietly happening for over 40 years. The main demonstrators have been petroleum companies, primarily as part of a process called enhanced oil recovery, which involves injecting CO2 and water into oil reservoirs to flush out residual oil. Since 1972 over 175 million metric tons of CO2 have been injected over 6,000 feet deep into the Canyon Reef limestone that lies beneath Texas’ SACROC oil field. So far, studies of the groundwater above this field haven’t shown any evidence of contamination.

Though a number of organizations, like GreenPeace, question whether stored gas will stay where we put it, a growing weight of modeling suggests that CO2 can be stored safely. In a 2005 Special Report on CCS, the IPCC characterized the storage aspect as one of low risk if – and it’s a heavy if – storage sites are properly managed. The report reads, “The fraction [of CO2] retained in appropriately selected and managed geological reservoirs is very likely to exceed 99 percent over 100 years and likely to exceed 99 percent over 1,000 years.” The same report also suggests that our earth has ample storage reservoirs, enough for about 2,000 billion metric tons of CO2, or more than twice the current carbon budget.

The Department of Energy’s Carbon Storage Atlas, which characterizes the storage potential of geologic formations around the country, is even more bullish in its most recent estimates of storage capacity. The most current edition of the atlas estimates safe capacity (beneath U.S. soils alone) to be at least 2,600 billion metric tons of CO2. As explained in this 2009 Grist interview, however, truly assessing the safety of a particular storage site requires a site-specific geological assessment and not a loose estimate based on general underground characteristics.


Critiques of BECCS

Despite the promise of negative emissions, BECCS can seem like a capitulation to a depressing status quo for anyone, like yours truly, who believes the heart-chilling threat of climate change needs to jolt our economy away from the kinds of destructive fuels and belief systems that got us into our current mess. But if we’re truly going to need to employ NETs, as the IPCC objectively tries to say we will, then we need to seriously consider the implications of the most hopeful one proposed so far.

At the heart of most critiques of BECCS is a fundamental uncertainty about the technology’s ability to work at the advertised scales. Kevin Anderson, Professor of Energy and Climate Change in the School of Mechanical, Aeronautical and Civil Engineering at the University of Manchester, has been one of the most incisive critics. In a 2016 Science paper, “The Trouble with Negative Emissions,” Anderson and co-author Glen Peters state, “Negative Emissions Technologies are not an insurance policy, but rather an unjust and high stakes gamble. There is a real risk that they will be unable to deliver on the scale of their promise.”

For these authors, the chance that BECCS doesn’t work makes the technology too risky to bet on as the “basis of a mitigation agenda.” By banking on a failing technology, they warn, we would fail to cut emissions enough in the short term, locking ourselves into a fatal high-emissions future. They conclude: “The mitigation agenda should proceed on the premise that [BECCS] will not work at scale.”

Climate scientist James Hansen shares a distrust in technologies that bias decision makers away from more immediate carbon reductions. In a paper titled “Young People’s Burden: Requirement of Negative CO2 Emissions,” published in Earth Systems Dynamics, Hansen and co-authors argue for the concept of “intergenerational justice.” They state that governments need to alter energy policies now to avoid sentencing “young people to either a massive, possibly implausible cleanup or growing deleterious climate impacts or both.” This paper makes the case for immediate and drastic emissions reductions combined with investments in proven carbon sinks like reforestation and improving soil fertility.

In addition to questioning scalability, critics also question the physical feasibility of going below net zero emissions. To truly reach negative numbers BECCS facilities will need to show a negative carbon balance over the lifecycle of the whole process and not just in the narrow band of time in which facilities produce power and suck up carbon. A 2016 study by Daniel Sanchez and Daniel Kammen of the University of California suggests that the biggest source of uncertainty in measuring lifecycle emissions of BECCS occurs not because of unknown fuel inputs, but because of the unknown effects of the massive land upheavals required by large scale BECCS.

In short, we don’t know how well all that biomass, and all that soil in which it grows, will actually absorb carbon compared to other possible land uses (say reforestation). It depends on the type of land used for production (are we clearcutting forests or are we restoring fallow farms?) and on how well soils and plants are able to store carbon in a warming world. Will climate change affect plant growth? And how will the changes to land, which will change how that land reflects or absorbs light, impact climate feedback cycles?

Besides emissions and storage questions, using massive amounts of land also creates unavoidable tradeoffs with the most valuable resources we’ve got – namely food, water, and biodiversity. A 2016 study published in Nature Climate Change provides a rough look at the resources required to achieve a median level of BECCS by 2100 according to IPCC models. The study estimates that growing swaths of the most efficient biomass crops like willow or poplar will require a land area of between 380 and 700 million hectares.

Even that low bound estimate is about 50 million hectares larger than the entire country of India, or over five times larger than the area of Texas. And even if we assume (as this report suggests the IPCC does) the use of abandoned farmland and rain-fed crops so as to avoid land or water stresses, estimating the productivity of such land is an exercise fraught with unknowns for the same reasons given above.

In addition to resource stresses from growing crops, the process of capturing and storing carbon also uses a lot of energy and water. The same Nature Climate Change study estimates that by 2100 BECCS will add to our current freshwater needs by about three percent. That’s a lot in an increasingly water-stressed world.

Finally, if the promise of CCS (used in conjunction with BECCS) is used to prop up industries like coal and gas-burning power plants, we will continue to face environmental costs besides those associated with emissions. As many concerned environmental groups have noted, continuing our addiction to fossil fuels means continuing processes of extracting and moving these fuels, processes which may create jobs but which aren’t exactly kind to the habitats and communities in the wake of mines or coal trains.

The above are a few of the most contentious risks attached with BECCS. Many more exist. Those hungry for more detailed critiques and perspectives can gorge on the info presented on Avoid2, a consortium of UK research organizations that does a thorough job scoring the potential costs and benefits of BECCS. Also, Sabine Fuss and her colleagues at the Mercator Research Institute on Global Commons and Climate Change have helped synthesize the uncertainties that surround BECCS and other NETs in order to help guide a meaningful research and policy agenda.

In a 2014 Nature Climate Change commentary, “Betting on Negative Emissions,” Fuss’s team lays out the “biophysical, technical, and social challenges” facing large-scale BECCS. They call for a “consistent narrative” around the technology, for research that better characterizes the prospects for negative emissions while also clarifying looming tradeoffs with land, food security, water, conservation, and biodiversity. In short, the team concludes, we need more research on the technology before betting on it.


Making a Safe Bet

It’s worth noting that the original intent of BECCS, as expressed by the engineers and scientists who first proposed the technology (called by a different name) in a peer-reviewed journal, was as a contingency plan to rigorous near-term emissions reductions. The title of this seminal paper, published in 2001 in Science, was “Managing climate risk.” The authors introduced BECCS as a risk management tool, not as a way to increase the carbon budget and delay climate action. A CarbonBrief piece, which traces the evolution of the concept and application of BECCS over the last two decades, offers this revealing quote from Michael Obersteiner, one of the paper’s lead authors:

“The argument of the 2001 paper was to use BECCS as a backstop technology in case we got bad news from the climate system (e.g. signs of abrupt climate change, unpleasant carbon cycle feedback). Thus, the strategy should be to plan climate mitigation for a still ambitious climate target without BECCS, but still prepare for it in terms of large scale afforestation and regeneration to be prepared for the backstop, if needed. All of the integrated assessment models (IAMs) are deterministic [ie, have a single outcome per model] and do not allow for risk management thinking.”

It’s also worth noting that most critics of BECCS don’t lobby to scrap the technology, or NETs in general. Even staunch skeptics like Kevin Anderson suggest that we continue to research BECCS and other NETs so that we can deploy them more knowingly and with a clear sense of their costs. Considering the urgency of cutting emissions, we cannot afford to take solutions off the table. We need to get the research right, and fast.

Research concerning BECCS and other NETs is exponentially expanding. A 2017 study by The Mercator Research Institute on Global Commons and Climate Change suggests that the number of academic papers on NETs has doubled about every 3.4 years from the turn of the century. Last year alone saw nearly 500 papers.

Tracking and synthesizing the information from such an exploding field and about so many different technologies, this study says, is becoming difficult for any individual to do. The job requires systematic forms of meta-analysis, and this study can serve as one early model. By looking across multiple examples of different types of negative emissions research, the study uncovers patterns and makes a few sensible recommendations about how to best bet on NETs.

First, the study suggests that we shouldn’t write off other technologies besides BECCS. “The integrated scenario literature,” the authors note, “has largely focused on removing carbon dioxide from the atmosphere by means of bioenergy in combination with carbon capture and storage (BECCS). But there are many other routes for extracting CO2 from the atmosphere that have not been comprehensively treated by the IPCC so far.”

Among other NETs the report considers: afforestation and reforestation, biochar and soil sequestration, and direct air capture. A realistic and resilient approach will need to be diverse, or a portfolio of negative emissions technologies. The authors write, “Prudence suggests that a portfolio of carbon dioxide removal options will be needed, with assessment of each NET underpinned by three important questions: 1) how much; 2) at what costs; 3) at what risks.”

In short, staking our future on one unproven technology is not a good plan. Staking it on many is better, but we still need a coherent and clear understanding of costs and risks. Best is to invest in a portfolio of NETs while in the meantime rigorously pursuing policies (binding international agreements and prices on carbon) and massive deployment of technologies (energy efficiency and renewables) that actually promise drastic carbon reductions.

And best, considering the slim timeline we’ve got to expend our carbon budget, is to invest in all of these technologies with the kind of governmental commitment that the current U.S. administration is so devastatingly dumping into the wrong kinds of national defense. The longer we delay making emission cuts, the more we’re relying on unproven NETs to work, and the faster we’re pushing our earth into a gamble that we can’t back out of.




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