The effects of air pollution on vegetation may provide an important control on the carbon cycle that has not yet been widely considered. Prolonged exposure to high levels of ozone, in particular, has been observed to inhibit photosynthesis by direct cellu lar damage within the leaves and through changes in stomatal conductance. We have incorporated empirical equations derived for trees (hardwoods and pines) and crops into the Terrestrial Ecosystem Model version 4.3 (TEM 4.3) to explore the effects of ozon e on net primary production and carbon sequestration across the conterminous United States. Our results show up to a 5% reduction in Net Primary Production (NPP) in response to modeled historical ozone levels during the late 1980s to early 1990s. The lar ge st decreases (over 20% in some locations) occur in the eastern U.S. and Midwest, during months with high ozone levels and high productivity. Carbon sequestration during the 1980s is reduced by 30 to 70 Tg C/yr with the presence of ozone, or 5 to 23% o f recent estimates of the total carbon sequestration for the U.S. Thus the effects of ozone on NPP and carbon sequestration should be factored into future calculations of the U.S. carbon budget. / Abstract in HTML and technical report in PDF available on the Massachusetts Institute of Technology Joint Program on the Science and Policy of Global Change Website. (http://mit.edu/globalchange/www/) / Includes bibliographical references (p. 20-21)

This paper uses bottom-up engineering information as a basis for modeling new technologies within the MIT Emissions Prediction and Policy Analysis (EPPA) model, a computable general equilibrium model of the world economy. Natural gas combined cycle (NGCC) without carbon capture and sequestration (CCS), natural gas combined cycle with CCS, and integrated coal gasification with CCS power generation technologies are introduced into the EPPA model. These compete in the electricity sector with conventional fos sil generation, nuclear, hydro, wind, and biomass power generation. Engineering cost data are used together with EPPA data, including the underlying Social Accounting Matrix (SAM) and supplementary physical energy accounts, to assure that technologies, w h en simulated within the model, meet thermodynamic efficiency limits, and that they reflect regional differences in the cost structure of the electric sector. Alternative capital vintaging approaches are investigated and an explicit treatment of market p enetration of new technologies is developed. Simulations through 2100 show the introduction of the new technologies and their decline as fuel and input prices, and carbon policies, change. A general result is that NGCC plants with or without capture, wh il e currently less costly methods of abating carbon emissions from the electric sector based on engineering data, play only a limited and short-term role in meeting carbon limits. By 2050 the coal CCS plants, currently the most costly of the three techno logies, dominate in the simulated policy scenarios because rising gas prices raise the cost of the gas-based technologies. / Abstract in HTML and technical report in PDF available on the Massachusetts Institute of Technology Joint Program on the Science and Policy of Global Change Website. (http://mit.edu/globalchange/www/) / Includes bibliographical references (p. 22).

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 10^22 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 mixing in the North Atlantic, and the reduction of Gent-McWilliams mixing in the Southern Ocean. / Abstract in HTML and technical report in PDF available on the Massachusetts Institute of Technology Joint Program on the Science and Policy of Global Change Website. (http://mit.edu/globalchange/www/) / Includes bibliographical references (p. 20-23).

Sensitivities of the net heat flux into the deep-ocean (Qnet) and of the deep-ocean heat content (DOC) below 700 m are studied using an ocean general circulation model and its adjoint. Both are found to have very similar sensitivities. The sensitivity to the surface freshwater flux (E-P-R) is positive in the Atlantic, but negative in the Pacific and Southern Ocean. A positive sensitivity to the downward net surface heat flux is found only in the North Atlantic north of 40 degrees N and the Southern Ocean. The diapycnal diffusivity of temperature affects Qnet and DOC positively in a large area of the tropics and subtropics in both the Pacific and Atlantic Ocean. The isopycnal diffusivity contributes to Qnet and DOC mainly in the Southern Ocean. Detailed analysis indicates that the surface freshwater flux affects Qnet and DOC by changing vertical velocity, temperature stratification, and overturning circulation. The downward net surface heat flux appears to increase Qnet and DOC by strengthening vertical advection and isopycnal mixing. The contribution of isopycnal diffusivity to Qnet and DOC is largely associated with the vertical heat flux due to isopycnal mixing. Similarly, the diapycnal diffusivity of temperature modulates Qnet and DOC through the downward heat flux due to diapycnal diffusion. The uncertainties of Qnet and DOC are estimated based on the sensitivities and error bars of observed surface forcing and oceanic diffusivities. For DOC, they are about 0.7 degrees K (1 degree K = 3 x 10^24 J) for the isopycnal diffusiv ity, 0.4 degrees K for the diapycnal diffusivity of temperature, 0.3 degrees K for the surface freshwater flux, and 0.1 degrees K for the net surface heat flux and zonal wind stress. Our results suggest that the heat uptake by ocean GCMs in climate experiments is sensitive to the isopycnal diffusivity as well to the diapycnal thermal diffusivity. / Abstract in HTML and technical report in PDF available on the Massachusetts Institute of Technology Joint Program on the Science and Policy of Global Change Website. (http://mit.edu/globalchange/www/) / Includes bibliographical references (p. 25-30).

As a consequence of the flexibility mechanisms incorporated in the Kyoto Protocol, incentive-based policies such as emissions trading and the clean development mechanism are being widely discussed in the context of greenhouse gas (GHG) abatement. This paper examines various issues related to incentive-based approaches for India. Some of the specific questions it addresses are: does India stand to gain or lose if emissions trading is realized even if it remains outside such an arrangement? Are there any other incentive-based approaches, e.g., carbon taxes that India could adopt? In the ultimate analysis, however, market-based instruments (MBIs) for GHG abatement in India cannot be viewed in isolation from an overall incentive-based orientation towards environmental policy as well as broader economic and legal reform that creates a suitable milieu for MBIs. Therefore, the paper goes on to examine problems of implementing MBIs in general, particularly those related to monitoring of emissions and of enforcement. Several specific solutions are also proposed. / Abstract in HTML and technical report in PDF available on the Massachusetts Institute of Technology Joint Program on the Science and Policy of Global Change Website. (http://mit.edu/globalchange/www/) / Includes bibliographical references (p. 24-26).

We consider the efficiency implications of policies to reduce global carbon emissions in a world with pre-existing tax distortions. We first show that the weak double dividend, the proposition that the welfare improvement from a tax reform where environme ntal taxes are used to lower distorting taxes must be greater than the welfare improvement from a reform where the environmental taxes are returned in a lump sum fashion, need not hold in a world with multiple distortions. A small analytic general equilib rium model is constructed to demonstrate this result. We then present a large-scale computable general equilibrium model of the world economy with distortionary taxation. We use this model to evaluate a number of policies to reduce carbon emissions. We find that the weak double dividend is not obtained in a number of European countries. Results also demonstrate the point that the interplay between carbon policies and pre-existing taxes can differ markedly across countries. Thus one must be cautious in extrapolating the results from a country specific analysis to other countries. / Abstract in HTML and technical report in PDF available on the Massachusetts Institute of Technology Joint Program on the Science and Policy of Global Change Website. (http://mit.edu/globalchange/www/) / Includes bibliographical references (p. 17-18).

The role of black carbon (BC) aerosols in climate change is important because of its strong capability in causing extinction of solar radiation. A three-dimensional interactive aerosol-climate model has been used to study the climatic impact of BC. The interannual variations of BC solar forcing derived from 20-year transient integrations are up to 4 times as large as the means mainly related to changes in cloud cover, snow depth (about +/- 20% over many high- or even mid-latitude regions in Northern Hemisphere) and thus the surface albedo, all caused by BC solar forcing itself. With an absolute amount three times higher than that of the top of the atmosphere (TOA) forcing, the surface forcing of BC is an extremely important factor in analyzing the climate impact of BC. BC aerosols cause a “cloud burning” effect in several polluted regions and a “cloud enhancing” effect in some high-latitude sites. Combined with BC-caused changes in surface albedo, this is defined as a non-Twomey-Albrecht indirect forcing by BC, which alters the radiative budgets by changing cloud cover and some land-surface properties thermodynamically rather than microphysically. The result of this study does not indicate that BC aerosols contribute to a significant increase in land-surface temperature with annual emissions of 14 TgC. The calculated surface temperature change is determined by a subtle balance among changes in surface energy sources and sinks as well as changes in the hydrological cycle, all caused by BC radiative forcing. The result of this study shows that the influence of BC aerosols on climate and environment at the regional scale is more significant than at the global scale. Several important feedbacks between BC radiative effect and climate dynamics revealed in this study suggest the importance of using interactive aerosol-climate models to address the issues related to the climate impacts of aerosols. / Abstract in HTML and technical report in PDF available on the Massachusetts Institute of Technology Joint Program on the Science and Policy of Global Change Website. (http://mit.edu/globalchange/www/) / Includes bibliographical references (p. 18-19). / Supported by the industrial consortium of the MIT Joint Program on the Science and Policy of Global Change and by the DOE DE-FG02-94ER61937 DE-FG02-93ER61713

In discussions of a cap-and-trade system for implementation of Kyoto Protocol-type quantity targets, a "safety valve" was proposed where, by government sales of emissions permits at a fixed price, the marginal cost of the effort could be limited to a predetermined level. The advantages seen for such a hybrid system included the shifting of the Kyoto architecture toward a price-based system, and the blunting of opposition to the Protocol on the basis of anticipated high cost. This paper reviews the theoretical underpinnings of the preference for a price instrument for controlling stock pollutants like greenhouse gases, and summarizes the arguments supporting and opposing the safety valve idea within the policy debate. If, in the face of uncertainty, emissions are to be limited to a fixed quantity target, then some means needs to be provided to avoid complete inflexibility. A safety valve can serve this function, although similar advantages can be achieved by the phasing in of quantity targets, coupled with provision for banking and borrowing. / Abstract in HTML and technical report in PDF available on the Massachusetts Institute of Technology Joint Program on the Science and Policy of Global Change Website. (http://mit.edu/globalchange/www/) / Includes bibliographical references (p. 11).

At meetings in Bonn and Marrakech in 2001, the Conference of the Parties to the Framework Convention on Climate Change broke through an impasse on the detailed provisions needed to allow the Kyoto Protocol to enter into force. Key ingredients in the breakthrough included U.S. withdrawal from the process, an effective relaxation of emissions targets for Japan, Canada, and Russia, and provision of access to unrestricted emissions trading. We analyze the costs of implementation and the environmental effectiveness of the Bonn-Marrakech agreement, and its effect on the relative roles of CO₂ vs. non-CO₂ greenhouse gases. The ability of the major sellers of permits, notably Russia and Ukraine, to restrict access to permits, and the ability to trade across all greenhouse gases controlled under the Protocol, are both found to have a significant effect for both costs and effectiveness. Finally, the implications of the agreement for the future evolution of the climate regime are explored. / Abstract in HTML and technical report in PDF available on the Massachusetts Institute of Technology Joint Program on the Science and Policy of Global Change Website. (http://mit.edu/globalchange/www/) / Includes bibliographical references (p. 16-17).

The transient response of both surface air temperature and deep ocean temperature to an increasing external forcing strongly depends on climate sensitivity and the rate of the heat mixing into the deep ocean, estimates for both of which have large uncertainty. In this paper we describe a method for estimating rates of oceanic heat uptake for coupled atmosphere/ocean general circulation models from results of transient climate change simulations. For models considered in this study, the estimates vary more than threefold. Nevertheless, values for all models fall in the 5-95% interval of the range implied by the climate record for the last century. The MIT 2D climate model, with an appropriate choice of parameters, matches changes in surface air temperature and sea level rise simulated by different models. It also reproduces the overall range of changes in precipitation. / Abstract in HTML and technical report in PDF available on the Massachusetts Institute of Technology Joint Program on the Science and Policy of Global Change Website. (http://mit.edu/globalchange/www/) / Includes bibliographical references (p. 12-14).