John M. DeCicco

Fuel Cell Vehicles

Fuel cells operating on hydrogen are among the propulsion technologies seeing research, development and demonstration as an option for meeting transportation needs in a world that faces severe limits on net anthropogenic CO 2 emissions. This article describes fuel cell vehicles, their principles of operation and major components while discussing the progress made in advancing the technology, the challenges it faces and its prospects for the future. Although various fuel cells can use different fuels, polymer electrolyte membrane (PEM) cells that use pure hydrogen are viewed as the best choice for motor vehicles. Fully capable automobiles using PEM fuel cells have been demonstrated and significant cost reductions are in sight for the vehicles themselves. Technical and economic hurdles remain for on-board hydrogen storage, refueling systems and hydrogen supply infrastructure. Fuel cell vehicles will also face competition from ongoing improvements in gasoline vehicles, including hybrid-electric designs, and in small car segments from battery electric vehicles. The economics of all such options will be evaluated in a context that includes increasing vehicle connectivity and automation as well as progress in the control of energy sector CO 2 emissions and programs for offsetting CO 2 emissions, particularly from liquid fuel use. Nevertheless, because of the promise they hold for meeting energy and climate challenges, fuel cell vehicles have captured the interest of governments and transportation industries around the world, and may become a viable choice for mobility systems of the future.

Biofuels and carbon management

Public policy supports biofuels for their benefits to agricultural economies, energy security and the environment. The environmental rationale is premised on greenhouse gas (GHG, “carbon”) emissions reduction, which is a matter of contention. This issue is challenging to resolve because of critical but difficult-to-verify assumptions in lifecycle analysis (LCA), limits of available data and disputes about system boundaries. Although LCA has been the presumptive basis of climate policy for fuels, careful consideration indicates that it is inappropriate for defining regulations. This paper proposes a method using annual basis carbon (ABC) accounting to track the stocks and flows of carbon and other relevant GHGs throughout fuel supply chains. Such an approach makes fuel and feedstock production facilities the focus of accounting while treating the CO2 emissions from fuel end-use at face value regardless of the origin of the fuel carbon (bio- or fossil). Integrated into cap-and-trade policy and including provisions for mitigating indirect land-use change impacts, also evaluated on an annual basis, an ABC approach would provide a sound carbon management framework for the transportation fuels sector.

Biofuel’s carbon balance: doubts, certainties and implications

Liquid fuels will remain valued energy carriers well into any upcoming period when CO2 reductions are sought. Biofuels are the presumed replacement for the petroleum-based transportation fuels that dominate liquid fuel use. Lifecycle analysis embeds a closed-loop model of biofuel-related carbon flows, making net CO2 uptake an assumption to be refuted. However, evaluating net CO2 uptake through dynamic industrial and agriforestry supply chains at real-world commercial scales is extremely difficult. All such estimates carry a great deal of doubt and cannot be verified empirically. A different perspective follows by anchoring analysis in the certainty that end-use CO2 emissions from biofuels are essentially the same as those of the petroleum fuels they replace. A first-order model of the globally coupled bio- and fossil-fuel system reveals conditions for biofuel use to provide an atmospheric benefit. No benefit occurs in the energy sectors where biofuels are used, but rather must be found elsewhere in locations of carbon absorption or retention. The implication is that climate mitigation efforts should focus on such locations and include any mechanisms through which net uptake (an enhanced sink or verifiable offset) can be achieved by biological, chemical, geological or other means. Although biofuels can play a mitigation role when certain conditions are met, deemphasizing biofuel production in favor of terrestrial carbon management may offer more immediate and effective ways to counterbalance the CO2 emitted when using carbon-based liquid fuels of any origin. Climate policies for transportation fuels should be reconsidered accordingly.

Annual Basis Carbon (ABC) Analysis of Biofuel Production at the Facility Level

Liquid biofuels such as ethanol and biodiesel are considered important renewable replacements for petroleum fuels such as gasoline and diesel. Biomass-based energy carriers are traditionally treated as inherently carbon neutral, so that only the fossil-based carbon dioxide (CO2) and other non-CO2 greenhouse gas (GHG) emissions associated with their production are counted when assessing their global warming impact. This accounting convention is embedded by construction in lifecycle assessment (LCA) models, which on a direct basis (i.e., excluding economically induced effects) often find that biofuels from efficient industrial agricultural production systems reduce GHG emissions relative to their fossil fuel counterparts. LCA modeling can be subjected to an independent empirical test that bounds a biofuels potential GHG reduction within the dynamics of the terrestrial carbon cycle. Such a test can be performed using annual basis carbon (ABC) accounting, which entails spatially and temporally explicit analysis of the direct GHG exchanges between the atmosphere and a physical vehicle-fuel system. An ABC case study of a corn ethanol biorefinery and the farmland that supplies it shows that using the ethanol it produced instead of gasoline provided no significant reduction in GHG emissions, in contrast to an LCA result that found a 40% GHG reduction for the same facility. ABC accounting reveals that the renewable ethanol so produced was not carbon neutral when substituting for gasoline, and sensitivity analysis indicates that its net GHG emissions impacts are likely to higher than those of petroleum gasoline in practice.

Author’s response to commentary on “Carbon balance effects of U.S. biofuel production and use”

The impact of substituting biofuels for fossil fuels on carbon dioxide (CO2) emissions has been debated for many years. A reason for the lack of resolution is that the method widely used to address the question, lifecycle analysis (LCA), is subjective. Its results irreducibly depend on untestable assumptions, notably those pertaining to system boundaries but also those for representing market effects. The best one can do is empirically constrain estimates of net CO2 impact using data that characterize important aspects of the overall system. Our 2016 paper, “Carbon balance effects of U.S. biofuel production and use,” took such an approach, using field data to estimate the direct CO2 exchanges for a circumscribed vehicle-fuel system over the 2005–2013 period of expanding US biofuel use. De Kleine and colleagues criticize our work because it does not follow LCA conventions, arguing in particular for the primacy of the assumption that biofuels are inherently carbon neutral. This response refutes their critique; it reminds readers why the lifecycle paradigm fails for a dynamic system involving the terrestrial carbon cycle, stresses the need to bound an analysis of key carbon exchanges, and explains why the circular logic of LCA can be so beguiling.

Opinion: Reconsidering bioenergy given the urgency of climate protection

The use of bioenergy has grown rapidly in recent years, driven by policies partly premised on the belief that bioenergy can contribute to carbon dioxide (CO2) emissions mitigation. However, the experience with bioenergy production and the pressure it places on land, water, biodiversity, and other natural resources has raised questions about its merits. Recent studies offer a lesson: Bioenergy must be evaluated by addressing both the stocks and flows of the carbon cycle. Doing so clarifies that increasing the rate of carbon uptake in the biosphere is a necessary condition for atmospheric benefit, even before considering production-related lifecycle emissions and leakage effects due to land-use change. To maximize the role of the biosphere in mitigation, we must focus on and start with measurably raising rates of net carbon uptake on land—rather than seeking to use biomass for energy. The most ecologically sound, economical, and scalable ways to accomplish that task are by protecting and enhancing natural climate sinks. Rather than prioritizing bioenergy production, researchers and policymakers should pursue carbon management initiatives such as the reforestation project pictured here. Such efforts are much more likely to significantly reduce atmospheric CO2 concentrations in the near and medium term. Image courtesy of Lisa M. Dellwo (photographer). Hence, a major reprioritization of climate-related research, policy, and investment is urgently required, a move away from bioenergy and toward terrestrial carbon management (TCM). Researchers and policymakers must pursue actionable mitigation approaches that have the best chance of significantly reducing atmospheric CO2 concentrations in the near and medium term. When the biosphere is engaged, the emphasis should shift toward large-scale natural climate solutions, including the protection, restoration, and enhancement of forests and other terrestrial carbon sinks. As energy researchers and policy analysts have confronted the global warming problem over the past several decades, industrial-scale … [↵][1]1To whom correspondence should be addressed. Email: DeCicco{at}umich.edu. [1]: #xref-corresp-1-1

Spatial and Temporal Analysis of Carbon Sequestrations in the Conterminous United States

This study develops geospatial analysis of terrestrial carbon exchange for the conterminous United State and estimates large-scale NEP (net ecosystem production) dynamic from 2008 to 2013. We apply land-use and land-cover data in order to coherently include cropland, forest, wetland and other ecologically active landscapes in the mapping. Our results show a distribution of high harvest carbon release in the Corn Belt states, in addition to hot spots around the US in areas like Southern California and Arizona. Harvest carbon is low in areas in the southern United States, and central/southern Appalachian Mountains. We identify NEP changes for coupled agricultural, forest and other high-carbon-uptake ecosystems systems, conversions to and from crop, and land in frequent conversion among forest, wetland, pasture and rangeland. Findings from this study will provide important information to support and promote the co-production of science and decision-making.