Bruce A. McCarl

Greenhouse gas mitigation in agriculture

Agricultural lands occupy 37% of the earths land surface. Agriculture accounts for 52 and 84% of global anthropogenic methane and nitrous oxide emissions. Agricultural soils may also act as a sink or source for CO2, but the net flux is small. Many agricultural practices can potentially mitigate greenhouse gas (GHG) emissions, the most prominent of which are improved cropland and grazing land management and restoration of degraded lands and cultivated organic soils. Lower, but still significant mitigation potential is provided by water and rice management, set-aside, land use change and agroforestry, livestock management and manure management. The global technical mitigation potential from agriculture (excluding fossil fuel offsets from biomass) by 2030, considering all gases, is estimated to be approximately 5500–6000 Mt CO2-eq. yr−1, with economic potentials of approximately 1500–1600, 2500–2700 and 4000–4300 Mt CO2-eq. yr−1 at carbon prices of up to 20, up to 50 and up to 100 US

Trading Water for Carbon with Biological Carbon Sequestration

t CO2-eq.−1, respectively. In addition, GHG emissions could be reduced by substitution of fossil fuels for energy production by agricultural feedstocks (e.g. crop residues, dung and dedicated energy crops). The economic mitigation potential of biomass energy from agriculture is estimated to be 640, 2240 and 16 000 Mt CO2-eq. yr−1 at 0–20, 0–50 and 0–100 US

U.S. agriculture and climate change: New results

t CO2-eq.−1, respectively.

Economic Potential of Biomass Based Fuels for Greenhouse Gas Emission Mitigation

Carbon sequestration strategies highlight tree plantations without considering their full environmental consequences. We combined field research, synthesis of more than 600 observations, and climate and economic modeling to document substantial losses in stream flow, and increased soil salinization and acidification, with afforestation. Plantations decreased stream flow by 227 millimeters per year globally (52%), with 13% of streams drying completely for at least 1 year. Regional modeling of U.S. plantation scenarios suggests that climate feedbacks are unlikely to offset such water losses and could exacerbate them. Plantations can help control groundwater recharge and upwelling but reduce stream flow and salinize and acidify some soils.

Estimating Leakage from Forest Carbon Sequestration Programs

We examined the impacts on U.S. agriculture of transient climate change assimulated by 2 global general circulation models focusing on the decades ofthe 2030s and 2090s. We examined historical shifts in the location of cropsand trends in the variability of U.S. average crop yields, finding thatnon-climatic forces have likely dominated the north and westward movement ofcrops and the trends in yield variability. For the simulated future climateswe considered impacts on crops, grazing and pasture, livestock, pesticide use,irrigation water supply and demand, and the sensitivity to international tradeassumptions, finding that the aggregate of these effects were positive for theU.S. consumer but negative, due to declining crop prices, for producers. Weexamined the effects of potential changes in El Niño/SouthernOscillation (ENSO) and impacts on yield variability of changes in mean climateconditions. Increased losses occurred with ENSO intensity and frequencyincreases that could not be completely offset even if the events could beperfectly forecasted. Effects on yield variability of changes in meantemperatures were mixed. We also considered case study interactions ofclimate, agriculture, and the environment focusing on climate effects onnutrient loading to the Chesapeake Bay and groundwater depletion of theEdwards Aquifer that provides water for municipalities and agriculture to theSan Antonio, Texas area. While only case studies, these results suggestenvironmental targets such as pumping limits and changes in farm practices tolimit nutrient run-off would need to be tightened if current environmentalgoals were to be achieved under the climate scenarios we examined

Implications of a carbon-based energy tax for U.S. agriculture.

Use of biofuels diminishes fossil fuelcombustion thereby also reducing net greenhousegas emissions. However, subsidies are neededto make agricultural biofuel productioneconomically feasible. To explore the economicpotential of biofuels in a greenhouse gasmitigation market, we incorporate data onproduction and biofuel processing for thedesignated energy crops switchgrass, hybridpoplar, and willow in an U.S. AgriculturalSector Model along with data on traditionalcrop-livestock production and processing, andafforestation of cropland. Net emissioncoefficients on all included agriculturalpractices are estimated through crop growthsimulation models or taken from the literature. Potential emission mitigation policies ormarkets are simulated via hypothetical carbonprices. At each carbon price level, theAgricultural Sector Model computes the newmarket equilibrium, revealing agriculturalcommodity prices, regionally specificproduction, input use, and welfare levels,environmental impacts, and adoption ofalternative management practices such asbiofuel production. Results indicate no rolefor biofuels below carbon prices of

A reassessment of the economic effects of global climate change on U.S. agriculture

40 perton of carbon equivalent. At these incentivelevels, emission reductions via reduced soiltillage and afforestation are more costefficient. For carbon prices above

Cropping Activities in Agricultural Sector Models: A Methodological Proposal

70,biofuels dominate all other agriculturalmitigation strategies.

Enhancement of Carbon Sequestration in US Soils

Leakage from forest carbon sequestration—the amount of a program’s direct carbon benefits undermined by carbon releases else-where—depends critically on demanders’ ability to substitute non-reserved timber for timber targeted by the program. A nalytic, econometric, and sector-level optimization models are combined to estimate leakage from different forest carbon sequestration activities. Empirical estimates for the United States show leakage ranges from minimal (< 10%) to enormous (> 90%), depending on the activity and region. These results suggest that leakage effects should not be ignored in accounting for the net level of greenhouse gas offsets from land use and forestry mitigation activities. (JEL Q25, Q32)

Assessing effects of mitigation strategies for global climate change with an intertemporal model of the U.S. forest and agriculture sectors

Policies to mitigate greenhouse gas emissions are likely to increase energy prices. Higher energy prices raise farmer costs for diesel and other fuels, irrigation water, farm chemicals, and grain drying. Simultaneously, renewable energy options become more attractive to agricultural producers. We consider both of these impacts, estimating the economic and environmental consequences of higher energy prices on U.S. agriculture. To do this we employ a price-endogenous agricultural sector model and solve that model for a range of carbon-tax-based energy price changes. Our results show mostly positive impacts on net farm income in the intermediate run. Through market price adjustments, fossil fuel costs are largely passed on to consumers. Additional farm revenue arises from the production of biofuels when carbon taxes reach