Meeting future world energy needs while addressing climate change requires large-scale deployment of low or zero greenhouse gas (GHG) emission technologies such as wind energy. The widespread availability of wind power has fueled legitimate interest in this renewable energy source as one of the needed technologies. For very large-scale utilization of this resource, there are however potential environmental impacts, and also problems arising from its inherent intermittency, in addition to the present need to lower unit costs. To explore some of these issues, we use a three-dimensional climate model to simulate the potential climate effects associated with installation of wind-powered generators over vast areas of land or coastal ocean. Using windmills to meet 10% or more of global energy demand in 2100, could cause surface warming exceeding 1oC over land installations. In contrast, surface cooling exceeding 1°C is computed over ocean installations, but the validity of simulating the impacts of windmills by simply increasing the ocean surface drag needs further study. Significant warming or cooling remote from both the land and ocean installations, and alterations of the global distributions of rainfall and clouds also occur. These results are influenced by the competing effects of increases in roughness and decreases in wind speed on near-surface turbulent heat fluxes, the differing nature of land and ocean surface friction, and the dimensions of the installations parallel and perpendicular to the prevailing winds. These results are also dependent on the accuracy of the model used, and the realism of the methods applied to simulate windmills. Additional theory and new field observations will be required for their ultimate validation. Intermittency of wind power on daily, monthly and longer time scales as computed in these simulations and inferred from meteorological observations, poses a demand for one or more options to ensure reliability, including backup generation capacity, very long distance power transmission lines, and onsite energy storage, each with specific economic and/or technological challenges.

In this paper we investigate the potential production and implications of a global biofuels industry. We develop alternative approaches to the introduction of land as an economic factor input, in value and physical terms, into a computable general equilibrium framework. Both approach allows us to parameterize biomass production in a manner consistent with agro-engineering information on yields and a "second generation" cellulosic biomass conversion technology. We explicitly model land conversion from natural areas to agricultural use in two different ways: in one approach we introduce a land supply elasticity based on observed land supply responses and in the other we consider only the direct cost of conversion. We estimate biofuels production at the end of the century will reach 220 to 270 exajoules in a reference scenario and 320 to 370 exajoules under a global effort to mitigate greenhouse gas emissions. The version with the land supply elasticity allows much less conversion of land from natural areas, forcing intensification of production, especially on pasture and grazing land, whereas the pure conversion cost model leads to significant deforestation. The observed land conversion response we estimate may be a short-term response that does not fully reflect the effect of long-run pressure to convert land if rent differentials are sustained over 100 years. These different approaches emphasize the importance of reflecting the non-market value of land more fully in the modeling of the conversion decision.

The plug-in hybrid electric vehicle (PHEV) may offer a potential near term, low carbon alternative to today's gasoline- and diesel-powered vehicles. A representative vehicle technology that runs on electricity in addition to conventional fuels was introduced into the MIT Emissions Prediction and Policy Analysis (EPPA) model as a perfect substitute for internal combustion engine (ICE-only) vehicles in two likely early-adopting markets, the United States and Japan. We investigate the effect of relative vehicle cost and all-electric range on the timing of PHEV market entry in the presence and absence of an advanced cellulosic biofuels technology and a strong (450ppm) economy-wide carbon constraint. Vehicle cost could be a significant barrier to PHEV entry unless fairly aggressive goals for reducing battery costs are met. If a low cost vehicle is available we find that the PHEV has the potential to reduce CO2 emissions, refined oil demand, and under a carbon policy the required CO2 price in both the United States and Japan. The emissions reduction potential of PHEV adoption depends on the carbon intensity of electric power generation and the size of the vehicle fleet. Thus, the technology is much more effective in reducing CO2 emissions if adoption occurs under an economy-wide cap and trade system that also encourages low-carbon electricity generation.

The plug-in hybrid electric vehicle (PHEV) could significantly contribute to reductions in carbon dioxide emissions from personal vehicle transportation in the United States over the next century, depending on the cost-competitiveness of the vehicle, the relative cost of refined fuels and electricity, and the existence of an economy-wide carbon emissions constraint. Using a computable general equilibrium model, I evaluated the potential for the PHEV to enter the U.S. personal vehicle market before 2100 and alter electricity output, refined oil consumption, carbon dioxide emissions, and the economic welfare losses associated with the imposition of a strict climate policy. The PHEV is defined by its ability to run on battery-stored electricity supplied from the grid as well as on refined fuel in an internal combustion engine. Sectors that produce PHEV transportation as well as other electric-drive vehicle technologies were added to the MIT Emissions Prediction and Policy Analysis (EPPA) Model as a perfect substitute for internal combustion engine (ICE)-only vehicles. Engineering cost estimates for the PHEV, as well as information about the pre-existing fleet, were used to specify PHEV sector input shares and substitution elasticities in the model.

Based on the model results, several conclusions emerged from this work. First, lower vehicle cost markups may hasten PHEV market entry, especially in the absence of a climate policy. Second, in the short term, the lower cost of electricity compared with refined fuels on a per mile basis is likely to favor adoption of vehicles with longer all-electric ranges. However, realizing the electricity advantage will depend on whether or not current battery cost and performance limitations can be overcome. Third, the availability of biofuels as a carbon neutral fuel substitute could delay PHEV market entry, especially when a climate policy is imposed. Fourth, large-scale adoption of the PHEV will increase electricity demand, reduce refined oil consumption, and could offset the economic welfare cost of pursuing a climate policy, especially if biofuels are not available. Fifth, realizing the maximum carbon emissions reduction potential of grid-charged electric-drive vehicles such as the PHEV will depend on concurrent reductions in power sector emissions.