|Accelerated restoration in progress at the Malheur National Forest, Oregon [photo: U.S. Forest Service]
Protecting the Earth's climate takes on greater urgency every day. The vast majority of carbon dioxide (CO2) and other climate-wrecking greenhouse gas (GHG) emissions comes from the unmitigated use of fossil fuels. But that doesn't mean that every form of alternative energy is helpful for the planet. Case in point: bioenergy, such as liquid biofuels to replace oil or forest products to replace coal.
Indeed, using biomass for energy at large scales does not belong on the short list of actions to take for climate protection. This is the conclusion of a commentary by Bill Schlesinger and myself just published in the Proceedings of the National Academy of Sciences. Given the real-world limitations of not only technology but also land-use governance, we argue that the priority policymakers have given to promoting bioenergy is profoundly misplaced.
As bioenergy use has grown over the past decade and a half, so too has the evidence that the net effects on GHG emissions are marginal at best and that in many cases it makes matters worse. Extensive bioenergy use also harms biodiversity and worsens other environmental problems. Over a decade ago some astute analysts warned that biofuels might be a cure worse than the disease. We now know that the adverse impacts of bioenergy use are even worse than feared.
The bioenergy blunder is a morality tale of what can go wrong when researchers fail to adequately check their computer models. All of the modeling studies used to justify bioenergy were premised on the belief that it is inherently carbon neutral. This common assumption holds that the CO2 released when burning bioenergy products instead of fossil fuels does not increase the net amount of CO2 in the atmosphere because the emissions are fully offset by the CO2 absorbed when biomass is grown. But this assumption turns out to be simplistic and misleading; it is not a problem that can be patched over with ever more complex computer modeling, which only serves to make the results even more uncertain and difficult to verify.
The scientifically correct way to look at the situation starts with the fact that using bioenergy emits CO2 into the atmosphere at the same rate or faster than the fossil energy it replaces. The burden of proof then becomes whether diverting biomass for energy speeds up the rate at which CO2 is removed from the atmosphere by the biosphere. In other words, one must empirically check the additionality of the carbon accumulation in biomass harvested to replace fossil carbon.
In this context, once one realizes that CO2 mitigation requires increasing the net rate of carbon uptake, it is clear that there are much better ways to do that than bioenergy. First of all, it is crucial to redouble efforts to halt deforestation and the destruction of grasslands, peatlands and other carbon-rich ecosystems. Bioenergy increases the pressure to convert natural lands, which are already under stress due to the rising demand for food, feed and forest products. Moreover, there are many opportunities for natural climate solutions including reforestation, habitat restoration and rebuilding soil carbon.
Legitimate ways to reduce CO2 emissions from fossil fuel use include higher energy efficiency and truly carbon-free energy sources such as photovoltaics, wind and nuclear energy. Replacing fossil fuels with bioenergy does not "decarbonize" the energy system; it is a flawed strategy now and for the reasonably foreseeable future. The programs and policies devoted to bioenergy should be pared back and redirected toward greatly expanded efforts to protect terrestrial carbon stocks and recarbonize the biosphere.
DeCicco, J.M., and W.H. Schlesinger (2018) Reconsidering bioenergy given the urgency of climate protection. Proc Natl Acad Sci 115(39): 9642-45. http://doi.org/10.1073/pnas.1814120115
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Griscom, B.W., et al. (2017) Natural climate solutions. Proc Natl Acad Sci 114(44): 11645-50. https://doi.org/10.1073/pnas.1710465114
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