JP

Investigations of Cloud Altering Effects of Atmospheric Aerosols using a New Mixed Eulerian- Lagrangian Aerosol Model

Industry, urban development, and other anthropogenic influences have substantially altered the composition and size-distribution of atmospheric aerosol particles over the last century. This, in turn, has altered cloud albedo, lifetime, and patterns which together are thought to exert a negative radiative forcing on the climate; these are the indirect effects of atmospheric aerosols. The specifics of the process by which aerosol particles seed cloud particles are complex and highly uncertain. The goal of this thesis is to refine understanding of the role of various aerosol types in determining cloud properties. We approach this goal by constructing a new highly detailed aerosol-cloud process model that is designed to simulate condensation upon complex aerosol populations. We use this model to investigate the microphysics of aerosol-cloud interactions, specifically considering the role of cloud dynamics and of the ubiquitous mixed soot / sulfate aerosols.

We describe the Mixed Eulerian-Lagrangian Aerosol Model (MELAM). This new computer model of aerosol microphysics is specifically tailored to simulate condensation and activation as accurately as possible. It specifically calculates aerosol thermodynamics, condensation, coagulation, gas and aqueous phase chemistry, and dissolution. The model is able to consider inorganic aerosols and aerosols with both inorganics and insoluble cores; the specific chemical system to be considered is specified by the user in text input files. Aerosol particles may be represented using "sectional distributions" or using a "representative sample" distribution which tracks individual particles. We also develop a constant updraft speed, adiabatic parcel model and a variable updraft speed, episodically entraining parcel model to provide boundary conditions to MELAM and allow simulations of aerosol activation in cloud updrafts.

Using MELAM and the parcel models, we demonstrate that aerosol activation depends on the composition and size distribution of the sub-cloud aerosol population, on the updraft speed through a parcel's lifting condensation level, on the vertical profile of the updraft speed, and on entrainment. We use a convective parameterization that was developed for use in global or regional models to drive the episodically entraining, variable updraft speed parcel model. Ultimately, reducing the uncertainty of the global impact of the indirect effects of aerosols will depend on successfully linking cloud parameterizations to models of aerosol activation; our work represents a step in that direction.

We also consider the activation of mixed soot / sulfate particles in cloud updrafts. We constrain for the first time a model of condensation onto these mixed particles that incorporates the contact angle of the soot / solution interface and the size of the soot core. We find that as soot ages and its contact angle with water decreases, mixed soot / sulfate aerosols activate more readily than the equivalent sulfate aerosols that do not have soot inclusions. We use data from the Aerosol Characterization Experiments (ACE) 1 and 2, and from the Indian Ocean Experiment (INDOEX) to define representative aerosol distributions for clean, polluted, and very polluted marine environments. Using these distributions, we argue that the trace levels of soot observed in clean marine environments do not substantially impact aerosol activation, while the presence of soot significantly increases the number of aerosol that activate in polluted areas.

Iron conservation by reduction of metalloenzyme inventories in the marine diazotroph Crocosphaera watsonii

The marine nitrogen fixing microorganisms (diazotrophs) are a major source of nitrogen to open ocean ecosystems and are predicted to be limited by iron in most marine environments. Here we use global and targeted proteomic analyses on a key unicellular marine diazotroph Crocosphaera watsonii to reveal large scale diel changes in its proteome, including substantial variations in concentrations of iron metalloproteins involved in nitrogen fixation and photosynthesis, as well as nocturnal flavodoxin production. The daily synthesis and degradation of enzymes in coordination with their utilization results in a lowered cellular metalloenzyme inventory that requires ?40% less iron than if these enzymes were maintained throughout the diel cycle. This strategy is energetically expensive, but appears to serve as an important adaptation for confronting the iron scarcity of the open oceans. A global numerical model of ocean circulation, biogeochemistry and ecosystems suggests that Crocosphaera's ability to reduce its iron-metalloenzyme inventory provides two advantages: It allows Crocosphaera to inhabit regions lower in iron and allows the same iron supply to support higher Crocosphaera biomass and nitrogen fixation than if they did not have this reduced iron requirement.

Iron limits the cell division rate of Prochlorococcus in the eastern equatorial Pacific

Prochlorococcus, a small unicellular cyanobacterium, is an important member of the phytoplankton community in the eastern equatorial Pacific. When these waters were enriched with iron during IronEx II, the chlorophyll per cell and cell size of Prochlorococcus increased, implying that they were iron limited. The extent of this limitation was unclear, however, and the number of Prochlorococcus remained constant. To examine whether cell division rates were stimulated significantly by iron, we used a cell cycle analysis approach to measure them in and out of the Fe-enriched patch and in Fe-enriched bottles. The cell division rate increased from 0.6 to 1.1 d-1 over 6 d of exposure to the elevated iron concentrations in the patch. Cells incubated in bottles with additional iron had rates of 1.4 d-1 or two doublings per day. Prochlorococcus mortality rates, measured independently, nearly doubled after the addition of iron. This matched the increase in the cell division rate and maintained a relatively constant population size. Thus the cell division rates of even the smallest phytoplankton in the equatorial Pacific are significantly iron limited, but biomass is constrained by both iron limitation and microzooplankton grazing. The differential response of individual phytoplankton groups to the addition of iron during IronEx II was at least partially a result of differential mortality rates over the time course of the experiment. How the community would respond to sustained fertilization, however, is not obvious.

© 2000 American Society of Limnology & Oceanography

Irreversibility, uncertainty, and learning: portraits of adaptation to long-term climate change

The usefulness of adaptation strategies to changing climate depends on the characteristics of the system that must adapt. Divergent views on whether climate change will seriously affect society and what society can do about it can be traced, in part, to divergent views on these characteristics of systems. Issues of scale and how impacts are measured are also important. We identify a set of fundamental characteristics of natural systems and social systems that help to make underlying assumptions in climate change adaptation studies explicit. These are: Short-run autonomous flexibility; short-run non-autonomous flexibility; knowledge and capacity to undertake short-run actions; long-run autonomous flexibility; long-run non-autonomous flexibility; and knowledge and capacity to plan for and undertake adaptations that require changes in long- lived assets. Applications to crop agriculture and ecosystems illustrate how these portraits can be used. We find that if empirical research is to resolve questions of adaptability, more careful specification of the exact measure of impact and far richer models of the process of adaptation, able to test implicit assumptions in much of the existing empirical research, are needed.

© 2000 Kluwer Academic Publishers

Is international emissions trading always beneficial?

Economic efficiency is a major argument for international emissions trading under the Kyoto Protocol. We show that permit trading can be welfare decreasing for countries, even though private trading parties benefit. The result is a case of "immiserizing" growth in the sense of Bhagwati where the negative terms of trade and tax interaction effects wipe out the gains from trading. Simulation and welfare decomposition results based on a CGE model of the global economy show that under EU-wide trading countries that are net permit sellers generally lose, due primarily to the existence of distortionary energy taxes.

 

Is International Emissions Trading Always Beneficial?

Economic efficiency is a major argument for the inclusion of an international emission permit trading system under the Kyoto Protocol. Using a partial equilibrium framework, energy system models have shown that implementing tradable permits for greenhouse gases internationally could reduce compliance costs associated with the emission targets. However, we show that international emission trading could be welfare decreasing under a general equilibrium framework. We describe a case of immiserizing growth in the sense of Bhagwati where the negative terms of trade and tax-interaction effects wipeout the primary income gains from emission trading. Immiserizing emission trading occurs only when there are pre-existing distortions in the economy. Simulation results based on a CGE model developed at MIT (the EPPA model) show that under an EU-wide emission trading regime the introduction of a permit trading system cause welfare losses for some of the trading countries.

Japanese nuclear power and the Kyoto agreement

A global computable general equilibrium model is used to evaluate interactions of nuclear power and climate change policy in Japan. We find that to match official Japanese forecasts for nuclear power would require subsidies of 50 to 70 percent. We find that the carbon price is $20 to $40 (US 1995$) per ton higher compared with the unconstrained case if nuclear expansion is limited to plants already commissioned or under construction, a scenario whose likelihood increased as a result of the recent nuclear accident. J. Japan. Int. Econ., September 2000, 14(3), pp. 169–188. Joint Program on the Science and Policy of Global Change, 77 Massachusetts Avenue, Building E40-263, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139-4307.

Copyright 2000 Academic Press
 

Japanese Nuclear Power and the Kyoto Agreement

We find that, on an economic basis, nuclear power could make a substantial contribution for meeting the emissions target Japan agreed to in the Kyoto Protocol. It is unlikely however that the contribution would be as large as projected in official Japanese forecasts. The economic costs of the carbon constraint rise if siting, construction, and approval problems prevent the economically desirable level of expansion of nuclear power. We also evaluate the economic effects of subsidizing nuclear power to achieve the expansion projected in official forecasts. While the subsidy required is substantial, the economic welfare effects are relatively small because of second-best considerations. We use the EPPA model, a global computable general equilibrium model, in the analysis. Our estimates thus include the effects of changing world energy prices and terms of trade as they affect competitiveness of nuclear power and economic welfare.

Joint Implementation: Lessons from Title IV's Voluntary Compliance Programs

The United Nation's Framework Convention on Climate Change (FCCC), signed by more than 150 nations in June 1992, commits signatory countries to limit greenhouse gas (GHG) emissions to 1990 levels by the year 2000. Article 3.3 of the FCCC states that "efforts to address climate change may be carried out cooperatively by interested Parties" and "policies and measures to deal with climate change should be cost-effective so as to ensure global benefits at the lowest possible cost." These statements provide the basis for the concept of Joint Implementation (JI) and the development of an international system in tradeable emissions entitlements. Joint Implementation and tradeable emissions entitlements offer an opportunity to curb GHG emissions at a low-cost through international partnerships and cooperation.
      Title IV of the United States' 1990 Clean Air Act Amendments (CAAA), also known as the Acid Rain Program, is the largest public policy experiment in the use of tradeable permits. It also incorporates two voluntary compliance programs, the substitution and opt-in provisions. These programs are analogous to JI and therefore, provide instructive insight into the potential barriers to broad JI investment.
      The response to the substitution and opt-in programs has been significantly different. Many more units have entered the substitution program than the opt-in program. Based on an analysis of these programs, this paper concludes that high transaction costs, particularly the monitoring costs associated with Title IV compliance, deter potential opt-in participants from entering the Acid Rain Program. The differing response to Title IV's two voluntary programs suggests that transaction costs can be a substantial barrier to JI and that minimizing this cost is necessary for encouraging greater JI participation

Joint Implementation: Lessons from Title IV's Voluntary Compliance Programs

The United Nation's Framework Convention on Climate Change (FCCC), signed by more than 150 nations in June 1992, commits signatory countries to limit greenhouse gas (GHG) emissions to 1990 levels by the year 2000. Article 3.3 of the FCCC states that "efforts to address climate change may be carried out cooperatively by interested Parties" and "policies and measures to deal with climate change should be cost-effective so as to ensure global benefits at the lowest possible cost." These statements provide the basis for the concept of Joint Implementation (JI) and the development of an international system in tradeable emissions entitlements. Joint Implementation and tradeable emissions entitlements offer an opportunity to curb GHG emissions at a low-cost through international partnerships and cooperation.
      Title IV of the United States' 1990 Clean Air Act Amendments (CAAA), also known as the Acid Rain Program, is the largest public policy experiment in the use of tradeable permits. It also incorporates two voluntary compliance programs, the substitution and opt-in provisions. These programs are analogous to JI and therefore, provide instructive insight into the potential barriers to broad JI investment.
      The response to the substitution and opt-in programs has been significantly different. Many more units have entered the substitution program than the opt-in program. Based on an analysis of these programs, this paper concludes that high transaction costs, particularly the monitoring costs associated with Title IV compliance, deter potential opt-in participants from entering the Acid Rain Program. The differing response to Title IV's two voluntary programs suggests that transaction costs can be a substantial barrier to JI and that minimizing this cost is necessary for encouraging greater JI participation.

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