The Kathmandu Valley, Nepal, is a broad bowl-shaped basin in the Himalayan foothills, with a population of more than two million people. Its growing air pollution problem is strongly affected by wind systems generated by the heating and cooling of the surrounding topography. We carried out a field measurement campaign of air pollutants and meteorology in the Kathmandu Valley during the dry season 2004-2005, followed by MM5 simulations nested down to 1 km resolution. The model results have allowed us to interpret the observed distinct diurnal cycle and determine the major processes responsible for the observations. We found that, at night, the Kathmandu Valley behaves like a large basin, with down-slope flows on surrounding mountains contributing to an accumulating cold air pool that grows to the altitude of surrounding mountain passes. The arriving cold air pushes underneath the air mass polluted in the evening, lifting up layers of polluted air, while providing relatively clean conditions to the surface during pre-dawn hours. After sunrise the elevated layers re-circulate to the surface, leading to a sharp rise in pollution. During the morning a mixed layer begins to grow over the valley, but it peaks at mid-day. Further growth is stunted by the arrival through mountain passes of cooler air that originated over lower regions outside of the Kathmandu Valley. This creates a renewed stratification as cooler air spreads across valley bottom; such behavior has been observed elsewhere on a number of elevated plateaus. During the afternoon most of the valley's ventilation takes place at low elevations, with strong winds bringing background air through the western passes, while transporting polluted air out the eastern passes. Our study sheds light onto some of the complex patterns of air pollution transport that take places in polluted mountain areas, while helping guide future research, including a proposed study of the ventilation of Ganges Valley air through the Himalaya.

Using a global coupled model of intermediate complexity (2D atmosphere, 3D ocean), the behavior of the thermohaline circulation is explored for various increased CO2 scenarios. A novel feature of the model is our ability to adjust the model’s sensitivity to CO2 increases by changing the strength of the cloud feedback. By varying the rate and duration of increases in atmospheric CO2, the model’s sensitivity, and the river runoff scheme for perturbations in freshwater forcing, we are able to obtain and analyze a spectrum of behaviors, ranging from little change in the thermohaline circulation to a full shutdown of sinking in the North Atlantic. We find that the thermohaline circulation is particularly sensitive to changes in river runoff into the Arctic Ocean. The strength of the meridional overturning circulation in the Atlantic is compared to changes in the steric height difference between the North Atlantic and the South Atlantic.We find a strong correlation between changes in overturning strength and the strength of the steric height gradient; moreover, we find a reversal in the sign of the gradient when the circulation undergoes a collapse.

As nations engage in the long-term process of negotiating a protocol on controlling greenhouse gas emissions, the danger of costly mistakes looms large, both from doing too little or too much. Researchers try to provide insight and guidance on this difficult problem, many relying on the tools of mathematical simulation models, but two important shortcomings remain in much of the current analysis. One is the treatment of the uncertainty inherent in projections of economic activity over the next century or more; and the other is the way economic activity is modeled to impact the poorly understood physical and biological systems of the earth.
    This paper presents several simple illustrations of the performance of current policy proposals in the face of a long-term climate-based goal when uncertainties in economic growth and technology development are made explicit. Several conclusions emerge. Analyses that rely on deterministic emissions paths through time obscure the underlying uncertainties, and explicitly incorporating these uncertainties can produce qualitatively different conclusions. Moreover, apparent differences in the climate impacts of proposals now being debated within the Framework Convention on Climate Change may be negligible when viewed in the light of likely uncertainties. Seeking a less stringent protocol with a higher probability of compliance may thus produce preferable outcomes. Most importantly, the analyses presented are meant to highlight the need for flexibility in any response to climate change, because uncertainty is an unavoidable aspect of the problem.

We examine the effect of biofuels mandates and climate policy on the European vehicle fleet, in particular the prospects for diesel and gasoline vehicles. Our analysis is based on a dynamic computable general equilibrium model of the world economy which explicitly incorporates current generation biofuels, accounts for stock turnover of the vehicle fleets, disaggregates gasoline and diesel cars, and represents an advanced E85 vehicle. We find that the European vehicle fleet is robust to proposed biofuels mandates owing to an existing fuel tax and tariffs structure that favours diesel vehicles. Harmonising excise duties on diesel and gasoline or lowering tariffs on biofuel imports, however, is shown to reverse the trend toward more diesel vehicles and significantly alters the efficiency costs and environmental effectiveness of renewable fuel policies.

© 2012 Journal of Transport Economics and Policy