We investigate effects of 2000–2050 emissions and climate changes on the atmospheric transport of three polycyclic aromatic hydrocarbons (PAHs): phenanthrene (PHE), pyrene (PYR), and benzo[a]pyrene (BaP). We use the GEOS-Chem model coupled to meteorology from a general circulation model and focus on impacts to northern hemisphere midlatitudes and the Arctic. We project declines in anthropogenic emissions (up to 20%) and concentrations (up to 37%), with particle-bound PAHs declining more, and greater declines in midlatitudes versus the Arctic. Climate change causes relatively minor increases in midlatitude concentrations for the more volatile PHE and PYR (up to 4%) and decreases (3%) for particle-bound BaP. In the Arctic, all PAHs decline slightly under future climate (up to 2%). Overall, we observe a small 2050 “climate penalty” for volatile PAHs and “climate benefit” for particle-bound PAHs. The degree of penalty or benefit depends on competition between deposition and surface-to-air fluxes of previously deposited PAHs. Particles and temperature have greater impacts on future transport than oxidants, with particle changes alone accounting for 15% of BaP decline under 2050 emissions. Higher temperatures drive increasing surface-to-air fluxes that cause PHE and PYR climate penalties. Simulations suggest ratios of more-to-less volatile species can be used to diagnose signals of climate versus emissions and that these signals are best observed in the Arctic.

© 2013 American Chemical Society

In this study, we analyze changes in extreme temperature and precipitation over the US in a 60-member ensemble simulation of the 21st century with the Massachusetts Institute of Technology (MIT) Integrated Global System Model–Community Atmosphere Model (IGSM-CAM). Four values of climate sensitivity, three emissions scenarios and five initial conditions are considered. The results show a general intensification and an increase in the frequency of extreme hot temperatures and extreme precipitation events over most of the US. Extreme cold temperatures are projected to decrease in intensity and frequency, especially over the northern parts of the US. This study displays a wide range of future changes in extreme events in the US, even simulated by a single climate model. Results clearly show that the choice of policy is the largest source of uncertainty in the magnitude of the changes. The impact of the climate sensitivity is largest for the unconstrained emissions scenario and the implementation of a stabilization scenario drastically reduces the changes in extremes, even for the highest climate sensitivity considered. Finally, simulations with different initial conditions show conspicuously different patterns and magnitudes of changes in extreme events, underlining the role of natural variability in projections of changes in extreme events.

© 2014 the authors

Electronic supplementary material

The online version of this journal article (doi:10.1007/s10584-013-1048-1) contains supplementary material, which is available to authorized users.

This article is part of a Special Issue on “A Multi-Model Framework to Achieve Consistent Evaluation of Climate Change Impacts in the United States” edited by Jeremy Martinich, John Reilly, Stephanie Waldhoff, Marcus Sarofim, and James McFarland.

Due to their reliance on rain-fed agriculture, both as a source of income and consumption, many low-income countries are considered to be the most vulnerable to climate change. Here, we estimate the impact of climate change on food security in Tanzania. Representative climate projections are used in calibrated crop models to predict crop yield changes for 110 districts in Tanzania. These results are in turn imposed on a highly disaggregated, recursive dynamic economy-wide model of Tanzania. We find that, relative to a no-climate-change baseline and considering domestic agricultural production as the channel of impact, food security in Tanzania appears likely to deteriorate as a consequence of climate change. The analysis points to a high degree of diversity of outcomes (including some favorable outcomes) across climate scenarios, sectors, and regions. Noteworthy differences in impacts across households are also present both by region and by income category.

© 2012 Blackwell Publishing Ltd.

Air pollution has been recognized as a significant problem in China. In its Twelfth Five Year Plan (FYP), China proposes to reduce SO2 and NOx emissions significantly, and here we investigate the cost of achieving those reductions and the implications of doing so for CO2 emissions. We extend the analysis through 2050, and either hold emissions policy targets at the level specified in the Twelfth FYP, or continue to reduce them gradually. We apply a computable general equilibrium model of the Chinese economy that includes a representation of pollution abatement derived from detailed assessment of abatement technology and costs. We find that China’s SO2 and NOx emissions control targets would have substantial effects on CO2 emissions leading to emissions savings far beyond those we estimate would be needed to meet its CO2 intensity targets. However, the cost of achieving and maintaining the pollution targets can be quite high given the growing economy. In fact, we find that the Twelfth FYP pollution targets can be met while still expanding the use of coal, but if they are, then there is a lock-in effect that makes it more costly to maintain or further reduce emissions. That is, if firms were to look ahead to tighter targets, they would make different technology choices in the near term, largely turning away from increased use of coal immediately.