Are Land-use Emissions Scalable with Increasing Corn Ethanol Mandates in the United States?

In response to the Renewable Fuel Standard, the U.S. transportation sector now consumes a substantial amount (13.3 billion gallons in 2010) of ethanol. A key motivation for these mandates is to expand the consumption of biofuels in road transportation to both reduce foreign oil dependency and to reduce greenhouse gas (GHG) emissions from the consumption of fossil fuels in transportation. In this paper, we present the impacts of several biofuels expansion scenarios for the U.S. in which scaled increases in the U.S. corn ethanol mandates are modeled to explore the scalability of GHG impacts. The impacts show both expected and surprising results. As expected, the area of land used to grow biofuel crops increases with the size of the policy in the U.S., and some land-use changes occur abroad due to trade in agricultural commodities. Because the land-use changes happen largely in the U.S., there is an increase in U.S. land-use emissions when natural lands are converted to agricultural use in the policy scenarios. Further, the emissions impacts in the U.S. and the rest of the world in these scenarios, including land-use emissions, scale in direct proportion to the size of the U.S. corn ethanol mandates. On the other hand, the land-use emissions that occur in the rest of the world are disproportionately larger per hectare of change due to conversions of more carbon-rich forests to cultivate crops and feed livestock.We gratefully acknowledge the financial support for this work from the U.S. Department of Energy, Office of Science under DE-FG02-94ER61937, the U.S. Environmental Protection Agency under XA-83600001-1 and XA-835055101-2, and other government, industry, and foundation sponsors of the Joint Program on the Science and Policy of Global Change

A limiting velocity for quarkonium propagation in a strongly coupled plasma via AdS/CFT

We study the dispersion relations of mesons in a particular hot strongly coupled supersymmetric gauge theory plasma. We find that at large momentum k the dispersion relations become omega = v_0 k + a + b/k + ..., where the limiting velocity v_0 is the same for mesons with any quantum numbers and depends only on the ratio of the temperature to the quark mass T/m_q. We compute a and b in terms of the meson quantum numbers and T/m_q. The limiting meson velocity v_0 becomes much smaller than the speed of light at temperatures below but close to T_diss, the temperature above which no meson bound states at rest in the plasma are found. From our result for v_0, we find that the temperature above which no meson bound states with velocity v exist is T_diss(v) \simeq (1-v^2)^(1/4) T_diss, up to few percent corrections.We thus confirm by direct calculation of meson dispersion relations a result inferred indirectly in previous work via analysis of the screening length between a static quark and antiquark in a moving plasma. Although we do not do our calculations in QCD, we argue that the qualitative features of the dispersion relation we compute, including in particular the relation between dissociation temperature and meson velocity, may apply to bottomonium and charmonium mesons propagating in the strongly coupled plasma of QCD. We discuss how our results can contribute to understanding quarkonium physics in heavy ion collisions.Comment: 57 pages, 12 figures; references adde

The Future of U.S. Natural Gas Production, Use, and Trade

Two computable general equilibrium models, one global and the other providing U.S. regional detail, are applied to analysis of the future of U.S. natural gas as an input to an MIT interdisciplinary study The Future of Natural Gas. The focus is on uncertainties including the scale and cost of gas resources, the costs of competing technologies, the pattern of greenhouse gas mitigation, and the evolution of global natural gas markets. Results show that the outlook for gas over the next several decades is very favorable. In electric generation, given the unproven and relatively high cost of other low-carbon generation alternatives, gas is likely the preferred alternative to coal. A broad GHG pricing policy would increase gas use in generation but reduce use in other sectors, on balance increasing its role from present levels. The shale gas resource is a major contributor to this optimistic view of the future of gas. Gas can be an effective bridge to a lower emissions future, but investment in the development of still lower CO2 technologies remains an important priority. Also, international gas resources may well prove to be less costly than those in the U.S., except for the lowest-cost domestic shale resources, and the emergence of an integrated global gas market could result in significant U.S. gas imports

The Future of U.S. Natural Gas Production, Use, and Trade

Two computable general equilibrium models, one global and the other providing U.S. regional detail, are applied to analysis of the future of U.S. natural gas as an input to an MIT interdisciplinary study The Future of Natural Gas. The focus is on uncertainties including the scale and cost of gas resources, the costs of competing technologies, the pattern of greenhouse gas mitigation, and the evolution of global natural gas markets. Results show that the outlook for gas over the next several decades is very favorable. In electric generation, given the unproven and relatively high cost of other low-carbon generation alternatives, gas is likely the preferred alternative to coal. A broad GHG pricing policy would increase gas use in generation but reduce use in other sectors, on balance increasing its role from present levels. The shale gas resource is a major contributor to this optimistic view of the future of gas. Gas can be an effective bridge to a lower emissions future, but investment in the development of still lower CO2 technologies remains an important priority. Also, international gas resources may well prove to be less costly than those in the U.S., except for the lowest-cost domestic shale resources, and the emergence of an integrated global gas market could result in significant U.S. gas imports

Toward a consistent modeling framework to assess multi-sectoral climate impacts

Efforts to estimate the physical and economic impacts of future climate change face substantial challenges. To enrich the currently popular approaches to impact analysis - which involve evaluation of a damage function or multi-model comparisons based on a limited number of standardized scenarios - we propose integrating a geospatially resolved physical representation of impacts into a coupled human-Earth system modeling framework. Large internationally coordinated exercises cannot easily respond to new policy targets and the implementation of standard scenarios across models, institutions and research communities can yield inconsistent estimates. Here, we argue for a shift toward the use of a self-consistent integrated modeling framework to assess climate impacts, and discuss ways the integrated assessment modeling community can move in this direction. We then demonstrate the capabilities of such a modeling framework by conducting a multi-sectoral assessment of climate impacts under a range of consistent and integrated economic and climate scenarios that are responsive to new policies and business expectations