Behind the paper: a biophysical and public need perspective on carbon dioxide removal

In this post, we speak to the authors of the recent PLOS Climate article “Carbon dioxide removal–What’s worth doing? A biophysical and public need perspective“– June Sekera, Dominique Cagalanan, Amy Swan, Richard Birdsey, Neva Goodwin and Andreas Lichtenberger- about the story behind the research.

What led you to decide on your research question?

So-called “carbon capture” has become a focal point in many policy conversations, in the U.S. and elsewhere, about governments’ options for slowing climate change. The academic literature on “carbon capture and storage” (CCS) and “carbon dioxide removal” (CDR) is growing exponentially faster than the literature on climate change itself. And many of the academic papers are focused on how government can open up market opportunities for carbon capture businesses.

But the question that governments need to address is: what methods are worth doing from the perspective of public need, rather than market dynamics? The question that follows is: how can policymakers evaluate the options?  Few policymakers are able to read and absorb the vast academic literature on carbon capture. To make matters worse, the crucial information on biophysical dynamics, constraints and impacts is generally cloaked in arcane language and obscure metrics. Our study was aimed at addressing these problems.

How did you go about designing your study?

Our chief concern was making the vast amount of information and data on mechanical carbon capture and biological carbon sequestration accessible to policymakers. So we needed to present the information in a way that is meaningful to public policy decision-making. The first, and obvious, question is: which methods “work”? Determining effectiveness immediately puts one into the realm of biophysics – the basic laws of nature. 

Secondly, if a method is biophysically effective at removing CO2 from the atmosphere, what will it “cost” nations in terms of resource usage – energy, land, water?  In order to have relevance to policymaking, this question must be addressed by looking at operations at a climate-significant scale. Resource consumption at the small-scale testing level of operation of mechanical carbon capture happening now is not meaningful for policymaking.

Thirdly, policymakers need to know: what will be the co-impacts of each method on people and places?  Mechanical methods like CCS and “direct air capture” are industrial processes that use large amounts of hazardous chemicals, would require thousands of miles of pipelines and drilling of injection wells, and the underground storage of a hazardous material in a pressurized state. In contrast, biological sequestration methods have generally positive co-benefits, including improving climate resilience.  We needed to look at the question of co-impacts so that policymakers could factor those into their decision-making.

Did you encounter any challenges in collecting or interpreting your data?

Two challenges. One was figuring out how to compile the data in a way that could yield meaningful “apples-to-apples” comparisons between the two general approaches to carbon dioxide removal: mechanical capture and biological sequestration. This is particularly relevant when trying to compare resource usage at scale.  So, unlike most other studies, we standardized for outcome in order to compare input requirements. That is, we framed the question as: what quantity of resources – energy and land – would be required for removal of 1 Gt (gigaton; one billion tons) of CO2 a year?

Second, we needed not only to compile, but also to present, the data on biological sequestration in a way that is policymaker-relevant. This is particularly true for land usage, since it is often alleged that biological methods will crowd out land usage for growing food. So, we constructed a “building block” approach. The data are displayed in a spreadsheet that shows how much carbon is sequestered per acre. That is a very different approach than other studies take. With our approach, policymakers can see the ”sequestration capability” of each biological system – forests, farms, grasslands or wetlands. The data are for the U.S., but other nations, or even provinces, could enter the data for their own geographic area and determine the amount of land that would yield a particular amount of sequestration.

What struck you most about your results? What are the key messages and who do you hope might benefit from these new insights?

What is most striking about the results is how clear they are in showing that biological methods of carbon removal (like forest preservation, reforestation, accelerating urban tree cover and restoring grasslands and wetlands) are more resource-efficient and more effective in removing CO2 from the atmosphere at a climate-relevant scale and within the necessary time-frame. The results show that mechanical methods are mostly ineffective, significantly resource-inefficient and unable to make a difference within the urgent decades of the 2020s-2030s. The one mechanical method that could be effective at removal (“direct air capture” when one hundred percent renewables-powered) would require a vast amount of land — far more than is generally disclosed or recognized. Biological methods have positive co-impacts whereas mechanical methods are associated with harmful – and serious – co-impacts on people and places, which typically hit rural communities, poor people and people of color first and worst. Biological methods are also far less expensive. These are key messages that urgently need to be taken in by policy-makers who are in a position to direct financial resources to realistically address the climate crisis.

What further research would you like to see in this area?

More work is needed on resource consumption by carbon removal methods at climate-significant scale. We only looked at energy and land. We didn’t have the time or capacity to address water consumption by mechanical capture and storage as compared to biological sequestration. This comparison is sorely needed so that policymakers can take into consideration water requirements, as availability of this resource becomes so much more precarious and uneven.

What made you choose PLOS Climate as a venue for your article?

We selected PLOS Climate as a venue for our article primarily because of: 1. the strong topical fit with the aims and scope of the journal; 2. the timely review and publication process; and 3. the ability to publish Open Access.