Fourty percent of all crops grown in the world today are grown using irrigation, and shifting precipitation patterns due to climate change are viewed as a major threat to food security. This thesis examines, in the framework of the MIT Integrated Global System Model, the potential impacts of climate change on crop water stress and the risk implications for policy makers due to underlying uncertainty in climate models. This thesis presents the Community Land Model - Agriculture module (CLM-AG) that models crop growth and water stress. It is a global generic crop model built in the framework of the Community Land Model and was evaluated for maize, cotton and spring wheat. A full climate model, the IGSM-CAM, was first used to force CLM-AG and show the regional disparity of the response to climate change. Some areas like the Midwest or Equatorial Africa benefit from the higher precipitations associated to climate change while others like Europe or Southern Africa see the irrigation need for crops increase. The effect of a mitigation policy appeared contrasted, as water-stress for some areas (including Europe and Africa) is increased if greenhouse gases emissions are limited while for other areas (Central Asia, United States) it is reduced. A second analysis was carried in Central Zambia using uncertainty ensembles. The ensembles demonstrate the notable extent of the uncertainty stemming from different climate sensitivities and different regional patterns in climate models. Crops are impacted differently but a consistent result is that climate mitigation policies reduce uncertainty in crop water stress, making it easier to plan for any anticipated future climate change.

Nitrous oxide is an important greenhouse gas and ozone-depleting-substance. Its sources are diffuse and poorly characterized, complicating efforts to understand anthropogenic impacts and develop mitigation policies. Online, spectroscopic analysis of N2O isotopic composition can provide continuous measurements at high time resolution, giving new insight into N2O sources, sinks, and chemistry. We present a new preconcentration unit, “Stheno II”, coupled to a tunable infrared laser direct absorption spectroscopy (TILDAS) instrument, to measure ambient-level variations in 18O and sitespecific 15N N2O isotopic composition at remote sites with a temporal resolution of <1 h. Trapping of N2O is quantitative up to a sample size of ∼4 L, with an optimal sample size of 1200− 1800 mL at a sampling frequency of 28 min. Line shape variations with the partial pressure of the major matrix gases N2/O2 and CO2 are measured, and show that characterization of both pressure broadening and Dicke narrowing is necessary for an optimal spectral fit. Partial pressure variations of CO2 and bath gas result in a linear isotopic measurement offset of 2.6−6.0 ‰ mbar−1. Comparison of IR MS and TILDAS measurements shows that the TILDAS technique is accurate and precise, and less susceptible to interferences than IR MS measurements. Two weeks of measurements of N2O isotopic composition from Cambridge, MA, in May 2013 are presented. The measurements show significant short-term variability in N2O isotopic composition larger than the measurement precision, in response to meteorological parameters such as atmospheric pressure and temperature.

© 2013 American Chemical Society

Following the failure in 2010 to pass a comprehensive cap-and-trade bill in the United States, analysts and policymakers have called for new or more stringent policies to curb GHG emissions in the electric power sector. In his 2011 State of the Union address, President Obama announced the goal of producing 80 percent of electricity from “clean” energy sources by 2035. The idea of a federal clean energy standard (CES) has been garnering bi-partisan support in Washington, D.C., and at latest count, thirty-six states (plus the District of Columbia) already employ renewable energy standards (RES) or CES programs, most of them mandating that 15 to 25 percent of total electricity production by 2020 has to come from renewable or “clean” sources (DSIRE, 2011). Energy standards in existing and proposed regulation differ with regard to the list of fuel sources included. Unlike a RES program, most CES proposals would credit not only renewable sources, like wind, solar, bio-power, hydropower and geothermal, but would also credit non-emitting non-renewable sources like nuclear energy, and would give partial crediting to certain other technologies, such as gas and coal technologies with carbon capture and storage (CCS), and natural gas combined cycle plants.

This paper examines the efficiency and distributional implications of RES and CES regulation in the U.S. electric power sector employing a numerical general equilibrium model that is uniquely well suited to assessing both economy-wide and electric sector impacts. We investigate the impacts of introducing a federal energy standard, formulated with and without a particular emphasis on incentivizing renewable energy, on economy-wide costs and emissions reductions, relating these impacts to changes in electricity capacity and generation (shifts to low carbon fuels and renewable sources), and changes in general equilibrium products and factor prices.

The papers in this special issue represent some of the most comprehensive analyses of the implications of climate change for developing countries undertaken to date. The papers employ a bottoms-up systems approach whereby the implications of climate change are evaluated using structural models of agriculture and infrastructure systems. The authors of the paper hail from multiple disciplines. This comprehensive, multi-disciplinary, structural approach is designed to allow for more robust insight into the potential implications of climate change. The approach also allows for experimentation with alternative policy options for achieving development objectives in the context of climate change.

© 2012 Blackwell Publishing Ltd.