This paper develops and applies methods to quantify and monetize projected impacts on terrestrial ecosystem carbon storage and areas burned by wildfires in the contiguous United States under scenarios with and without global greenhouse gas mitigation. The MC1 dynamic global vegetation model is used to develop physical impact projections using three climate models that project a range of future conditions. We also investigate the sensitivity of future climates to different initial conditions of the climate model. Our analysis reveals that mitigation, where global radiative forcing is stabilized at 3.7 W/m² in 2100, would consistently reduce areas burned from 2001 to 2100 by tens of millions of hectares. Monetized, these impacts are equivalent to potentially avoiding billions of dollars (discounted) in wildfire response costs. Impacts to terrestrial ecosystem carbon storage are less uniform, but changes are on the order of billions of tons over this time period. The equivalent social value of these changes in carbon storage ranges from hundreds of billions to trillions of dollars (discounted). The magnitude of these results highlights their importance when evaluating climate policy options. However, our results also show national outcomes are driven by a few regions and results are not uniform across regions, time periods, or models. Differences in the results based on the modeling approach and across initializing conditions also raise important questions about how variability in projected climates is accounted for, especially when considering impacts where extreme or threshold conditions are important.

© 2015 the authors

The European Union (EU) recently adopted CO₂ emissions mandates for new passenger cars, requiring steady reductions to 95 gCO₂/km in 2021. We use a multi-sector computable general equilibrium (CGE) model, which includes a private transportation sector with an empirically-based parameterization of the relationship between income growth and demand for vehicle miles traveled. The model also includes representation of fleet turnover, and opportunities for fuel use and emissions abatement, including representation of electric vehicles. We analyze the impact of the mandates on oil demand, CO₂ emissions, and economic welfare, and compare the results to an emission trading scenario that achieves identical emissions reductions. We find that vehicle emission standards reduce CO₂ emissions from transportation by about 50 MtCO₂ and lower the oil expenditures by about €6 billion, but at a net added cost of €12 billion in 2020. Tightening CO₂ standards further after 2021 would cost the EU economy an additional €24–63 billion in 2025, compared with an emission trading system that achieves the same economy-wide CO₂ reduction. We offer a discussion of the design features for incorporating transport into the emission trading system.

I present work on the relationship between inorganic atmospheric aerosol impacts and their precursor emissions from the United States of America. The inorganic aerosol ions nitrate (NO ^̶₃), sulfate (SO^{2 ̶}₄), and ammonium (NH⁺₄) form from emissions of nitrogen oxides (NO_x), sulfur dioxide (SO₂), and ammonia (NH₃). Emissions of NO_x and SO₂ in the US have recently decreased, by 42% and 62% respectively for annual totals between 2005 and 2012, in response to economic, political, and technological developments. Under such large changes, the processes of aerosol formation may behave nonlinearly. The sensitivity of aerosol impacts to future emissions reductions – the change in a metric per unit change in emissions – can be very different from the sensitivity to past reductions. In this thesis, I use a chemical transport model to examine the sensitivities, changes in sensitivities, and the importance of nonlinear interactions for both health and climate impacts of inorganic aerosols.

The first section of this thesis focuses on surface concentrations of inorganic fine particulate matter (PM_2.5), a relevant metric for human health. In winter, PM_2.5 across the central US is primarily composed of ammonium nitrate, whose formation is highly dependent on thermodynamics. The recent NO_x and associated total nitrate (HNO₃+NO ^̶₃) reductions have made aerosol formation in this region limited by total nitrate availability. Future NO_x emissions reductions will thus have a much larger impact than they would have in the past. In summer, SO^{2 ̶}₄ aerosols dominate PM_2.5. The reduced NO_x emissions lead to higher peroxide concentrations and faster aqueous SO₂ oxidation, without increasing sulfate wet deposition to the same degree. With faster oxidation, a larger fraction of the emitted SO₂ forms sulfate and particulate matter, increasing the sensitivity of surface aerosol concentrations to SO₂ emissions even as emissions themselves have decreased. These results suggest that NO_x and SO₂ emissions reductions will continue to improve US air quality.

The second section of this thesis focuses on sensitivities of the direct radiative effect (DRE) of inorganic aerosols to US emissions, a key quantity for studying climate impacts. The DRE and changes in DRE in winter are largest over the ocean. The summertime DRE includes a long tongue of advected aerosols over the Atlantic as well as a broad area of large DRE over the eastern US. As with surface concentrations, sensitivity of DRE to NO_x and SO₂ emissions increased between 2005 and 2012, while sensitivity to NH₃ emissions decreased. A simple scaling estimate of the DRE in the 2012 case from the 2005 DRE and sensitivities overestimates the magnitude of the DRE by 10.3mWm⁻² in January and 21.4mWm⁻² in July. These values are equivalent to underestimating the SO₂ emissions reductions by 13.6% and 10.6%, respectively. These processes cause small errors for climate studies that assume scaling of aerosol radiative effects for current conditions, but greater errors could occur under future emission changes.

International environmental negotiations often involve conflicts between developed and developing countries. However, considering environmental cooperation in a North-South dichotomy obscures important variation within the Global South, particularly as emerging economies become more important politically, economically, and environmentally. This article examines change in the Southern coalition in environmental negotiations, using the recently concluded Minamata Convention on Mercury as its primary case. Focusing on India and China, we argue that three key factors explain divergence in their positions as the negotiations progressed: domestic resources and regulatory politics, development constraints, and domestic scientific and technological capacity. We conclude that the intersection between scientific and technological development and domestic policy is of increasing importance in shaping emerging economies’ engagement in international environmental negotiations. We also discuss how this divergence is affecting international environmental cooperation on other issues, including the ozone and climate negotiations.