There is an emerging, unwarranted polarization in the debate about the value of natural climate solutions versus bioenergy – both pathways should be part of potential climate and carbon removal portfolios moving forward. Phil Robertson, Steve Hamilton, Keith Paustian, and I, Pete Smith, provide an evidence-based argument on a balanced approach in our paper “Land-Based Climate Solutions for the United States,” published in Global Change Biology (doi: 10.1111/gcb.16267). Our analysis suggests that such an approach for the U.S. can provide about 50% more mitigation than either approach alone, based on previous analyses.
Meeting global warming targets requires aggressive action on multiple fronts. Recent reports, like that from COP26 on the role of sustainable food systems in achieving climate objectives, highlight that we can’t address mitigation goals without fully engaging the agricultural sector – yet no available assessments combine both nature-based solutions (reforestation, grassland and wetland protection, and agricultural practice change) and cellulosic bioenergy for a single geographic region.
Collectively, these solutions might offer a suite of climate, biodiversity, and other benefits greater than if implemented individually. Nature-based solutions are largely constrained by the duration of carbon accrual in soils and forest biomass. Each of these carbon pools will eventually saturate. Bioenergy solutions can, however, last indefinitely but carry significant environmental risk if carelessly deployed.
Assessing the Mitigation Capacities of Nature-Based and Bioenergy Solutions
In our paper on Land-Based Climate Solutions for the United States, we detail a simplified scenario for the U.S. that illustrates the benefits of combining approaches. Our methodology involved first assigning a portion of non-forested former cropland to bioenergy sufficient to meet projected mid-century transportation needs, with the remainder assigned to nature-based solutions such as reforestation.
Next, bottom-up mitigation potentials for the aggregate contributions of crop, grazing, forest, and bioenergy lands were then assessed by using a Monte Carlo model that included conservative ranges for cost-effective local mitigation capacities, together with ranges for (a) areal extents that avoid double counting and include realistic adoption rates and (b) the projected duration of different carbon sinks.
The projected duration illustrates the net effect of eventually saturating soil carbon pools in the case of most strategies, and additionally saturating biomass carbon pools in the case of reforestation. Results show a conservative end-of-century mitigation capacity of 110 (57 – 178) Gt CO2e for the U.S., about 50% higher than existing estimates that prioritize nature-based or bioenergy solutions separately.
We acknowledge the uncertainties in our simple, bottom-up modelling approach, and we suggest that further research could reduce these uncertainties. However, we believe that there is sufficient confidence in the general magnitude and direction of a combined approach to plan for deployment now.
Looking Ahead: Scaling Both Nature-Based and Bioenergy Solutions
In short, our analysis indicates that the polarized debate about bioenergy versus natural climate solutions is unproductive, as we see the use of both approaches within sustainably managed landscapes as the way forward.
This study shows the contribution that land can make to climate change mitigation in the U.S., and that policy support needs to be strengthened both for advanced bioenergy production with carbon capture and storage, and for natural climate solutions, including: peatland/wetland restoration, reforestation, forest restoration, and reduced emissions for agriculture. Such policy is necessary if these options are to be scaled and the full potential realized. Resources should also be invested in monitoring, reporting and verification (MRV) systems to ensure the integrity of these promising land-based solutions.
As a Science Advisor at Carbon Direct, I bring my research to bear in evolving our approach to holistic carbon management, from evaluating project suppliers to advising clients on creating high-quality and diverse carbon portfolios. Learn more about Carbon Direct Inc.’s advisory services here.