JP

The Deep-Ocean Heat Uptake in Transient Climate Change

The deep-ocean heat uptake (DOHU) in transient climate changes is studied using an ocean general circulation model (OGCM) and its adjoint. The model configuration consists of idealized Pacific and Atlantic basins. The model is forced with the anomalies of surface heat and freshwater fluxes from a global warming scenario with a coupled model using the same ocean configuration. In the scenario CO2 concentration increases 1% per year. The heat uptake calculated from the coupled model and from the adjoint are virtually identical, showing that the heat uptake by the OGCM is a linear process. After 70 years the ocean heat uptake is almost evenly distributed within the layers above 200 m, between 200 and 700 m, and below 700 m (about 20 x 1022 J in each). The effect of anomalous surface fresh water flux on the DOHU is negligible. Analysis of CMIP-2 data for the same global warming scenario shows that qualitatively similar results apply to coupled atmosphere-ocean GCMs. The penetration of surface heat flux to the deep ocean in our OGCM occurs mainly in the North Atlantic and the Southern Ocean, since both the sensitivity of DOHU to the surface heat flux and the magnitude of anomalous surface heat flux are large in these two regions. The DOHU relies on the reduction of convection and Gent-McWilliams-Redi mixing in the North Atlantic, and the reduction of Gent-McWilliams- Redi mixing in the Southern Ocean.

The deep-ocean heat uptake in transient climate change

The deep-ocean heat uptake (DOHU) in transient climate changes is studied using an ocean general circulation model (OGCM) and its adjoint. The model configuration consists of idealized Pacific and Atlantic basins. The model is forced with the anomalies of surface heat and freshwater fluxes from a global warming scenario with a coupled model using the same ocean configuration. In the scenario CO2 concentration increases 1% per year. The heat uptake calculated from the coupled model and from the adjoint are virtually identical, showing that the heat uptake by the OGCM is a linear process. After 70 years the ocean heat uptake is almost evenly distributed within the layers above 200 m, between 200 and 700 m, and below 700 m (about 20 x 1022 J in each). The effect of anomalous surface fresh water flux on the DOHU is negligible. Analysis of CMIP-2 data for the same global warming scenario shows that qualitatively similar results apply to coupled atmosphere-ocean GCMs. The penetration of surface heat flux to the deep ocean in our OGCM occurs mainly in the North Atlantic and the Southern Ocean, since both the sensitivity of DOHU to the surface heat flux and the magnitude of anomalous surface heat flux are large in these two regions. The DOHU relies on the reduction of convection and Gent-McWilliams-Redi mixing in the North Atlantic, and the reduction of Gent-McWilliams- Redi mixing in the Southern Ocean.

© 2008 American Meteorological Society

The Diurnal Cycle of Air Pollution in the Kathmandu Valley, Nepal: Observations

During the dry season of 2004–2005 we carried out field measurements of air pollution and meteorology in the Kathmandu Valley, Nepal, a bowl?shaped urban basin in the Himalayan foothills of Nepal. We measured the trace gases carbon monoxide (CO) and ozone (O3) and particulates (PM10), as well as meteorological variables. In our field observations we noted a very regular pattern of morning and evening peaks in CO and PM10 occurring daily in the valley bottom, interspersed with low values in the afternoons and at night. This pattern occurred even on days with unusual timing of emissions and was influenced by the timing of ventilation from the valley. Meteorological variables showed great day?to?day similarity, with a strong westerly wind blowing through the valley from late morning until dusk. We found that the air mass on nearby mountaintops was disconnected from pollution within the valley during the night, but received significant pollution during the morning, when up?slope flows began. At a pass on the western edge of the valley we found a diurnal switch in wind direction, with an inflow from late morning until late evening, and an outflow during the rest of the time. We found that part of the morning peak in pollution was caused by recirculation of pollutants emitted the night before, which spend the night in elevated layers over the valley.

The dynamic response of the winter stratosphere to an equable climate surface temperature gradient

This work investigates the dynamic and thermal response of the winter stratosphere to the presence of a weak meridional surface temperature gradient. Previous work suggested that polar stratospheric clouds could have played a decisive role in maintaining high-latitude warmth, especially over continental interiors, during the polar nights of the late Paleocene and early Eocene epochs; both a chemical source of additional water vapor and a dynamical feedback between the surface climate and stratospheric temperatures have been proposed as mechanisms by which such clouds could form. A principal goal of this work is to investigate the latter problem using a general circulation model with stratospheric resolution that is forced with a very weak surface temperature gradient. It is found that temperatures in the lower stratosphere do not deviate significantly from the control run, which results from a robust flux of wave activity into the winter stratosphere. The strength of the stratosphere's residual circulation increases slightly in the presence of the weak gradient, as wavenumber 3 begins to propagate to stratospheric altitudes. Changes in the zonal wind field that allow for the altered propagation are in balance with a weakened temperature gradient through the full depth of the troposphere. These simulations also suggest that the tropospheric thermal stratification could be maintained by moist convection at all latitudes in warm climate states with a weak temperature gradient.

© 2007 American Meteorological Society

The Economic Impacts of Climate Change: Evidence from Agricultural Profits and Random Fluctuations in Weather

This paper measures the economic impact of climate change on US agricultural land by estimating the effect of random year-to-year variation in temperature and precipitation on agricultural profits. The preferred estimates indicate that climate change will increase annual profits by $1.3 billion in 2002 dollars (2002$) or 4 percent. This estimate is robust to numerous specification checks and relatively precise, so large negative or positive effects are unlikely. We also find the hedonic approach—which is the standard in the previous literature—to be unreliable because it produces estimates that are extremely sensitive to seemingly minor choices about control variables, sample, and weighting.

© American Economic Association 2008

The Economic Impacts of Climate Change: Evidence from Agricultural Profits and Random Fluctuations in Weather

This paper measures the economic impact of climate change on agricultural land in the United States by estimating the effect of the presumably random year-to-year variation in temperature and precipitation on agricultural profits. Using long-run climate change predictions from the Hadley 2 Model, the preferred estimates indicate that climate change will lead to a $1.1 billion (2002$) or 3.4% increase in annual profits. The 95% confidence interval ranges from -$1.8 billion to $4.0 billion and the impact is robust to a wide variety of specification checks, so large negative or positive effects are unlikely. There is considerable heterogeneity in the effect across the country with California's predicted impact equal to -$2.4 billion (or nearly 50% of state agricultural profits). Further, the analysis indicates that the predicted increases in temperature and precipitation will have virtually no effect on yields among the most important crops. These crop yield findings suggest that the small effect on profits is not due to short-run price increases. The paper also implements the hedonic approach that is predominant in the previous literature. We conclude that this approach may be unreliable, because it produces estimates of the effect of climate change that are very sensitive to seemingly minor decisions about the appropriate control variables, sample and weighting. Overall, the findings contradict the popular view that climate change will have substantial negative welfare consequences for the US agricultural sector.

The Effects of Changing Consumption Patterns on the Costs of Emission Restrictions

Models with time horizons of 100 years are customarily used to predict anthropogenic greenhouse gas emissions and to inform the different climate-change policy dialogues. Historical evidence indicates that over this time span the current consumption patterns in developing countries are likely to change substantially and to converge to the present patterns in developed countries. The implications of such changes on emissions profiles and on the costs of policies to curtail them in developing countries are crucial aspects of a comprehensive climate-change policy agenda. This study deals with modeling this type of non-homotheticity in consumption functions within the EPPA framework based on econometric estimation and the above assumption of convergence in consumption patterns.
        We find that the composition of consumption and the consequent implications for the sources of emissions would be different in the model with static consumption-function coefficients from that in the model with dynamic coefficients, even though the regional emissions profiles are virtually the same in the two cases. The differences have significant implications for the costs of emissions restrictions in developing countries. Our results suggest that the costs of emissions restrictions in developing countries would be higher if the changes in consumption patterns are taken account of than if they are ignored in the simulation model.

The Effects on Developing Countries of the Kyoto Protocol and CO2 Emissions Trading

This paper examines the effect of the Kyoto Protocol on developing economies using marginal abatement curves generated by MIT's Emissions Prediction and Policy Assessment model (EPPA). In particular, the paper addresses how developing countries are affected by the scope of CO2 emissions trading, by various limitations that Annex I countries might place on emissions trading, by the nature of the Clean Development Mechanism, and by changes in the international trade flows in conventional goods and services. In general, it is found that developing countries benefit from emissions trading, both from the new export opportunities and by the lesser distortion of Annex I economies. This effect is particularly pronounced for energy exporting countries since Annex I countries are able to substitute cheaper reductions of coal emissions in developing countries for more expensive reductions of oil emissions within Annex I. The paper also highlights the implications of the apparent inelastic demand for tradable permits from non-Annex I countries and the conflict between revenue maximization and other goals assigned to the Clean Development Mechanism.

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