More Info
Back to CalendarStratosphere-Troposphere Exchange: Inferences from the Isotopic Composition of Water
David KeithAir can cross the tropical tropopause either by large-scale ascent or in localized episodes associated with deep convection. Recent observations demonstrate that lower stratospheric water-vapor mixing ratios are well predicted by the mean tropical tropopause temperature. Special mechanisms such as dehydration in overshooting cumuli or localized stratosphere-troposphere exchange are thus no longer required to explain the water-vapor content of the stratosphere. However, these mechanisms are not ruled out. Current observations of water vapor and other tracers do not allow us to determine the relative importance of these processes.
Moyer et al. noted that HDO content of stratospheric water is incompatible with a simple model based on Rayleigh fractionation during ascent from sea surface to tropopause in a deep convective event. They suggested that the super-saturation or ice lofting could explain the discrepancy. Recent data on stratospheric H2018 suggests that super-saturation cannot be responsible. We consider the isotopic consequences of ice lofting by two mechanisms: (1) direct lofting of ice into the stratosphere associated with deep convection, or (2) lofting of ice to the upper troposphere, evaporation, and subsequent large-scale ascent into the stratosphere. A simple model indicates that either mechanism would be compatible with current observations of stratospheric water, but that observation of the isotopic composition of upper-tropospheric humidity could distinguish between these mechanisms.
Uncertainty, Short Term Hedging and The Tolerable Window Approach
Gary Yohe
Hedging strategies that minimize the expected discounted cost of restricting both temperature change and the rate of temperature change within ~tolerable windows~ defined by German researchers are explored. Targeting the smaller window prescribed by the German Advisory Board on Climate Change through the year 2020 emerges as the least cost strategy as this break-even likelihood, expected costs, even discounted according to the Ramsey optimal growth rule, amount to something on the order of $21 trillion (1990$). Since it is the rate of change constraint that binds more immediately, this estimate can be interpreted as the opportunity cost of limiting temperature change to no more than 0.2 degrees C per decade through the year 2020.
Studying the Human Dimensions of Forest Ecosystems in the Western Hemisphere: the CIPEC Research Strategy
Emilio Moran, Indiana University
The Center for the Study of Institutions, Population and Environmental Change focuses on the study of deforestation and afforestation processes as mediated by institutions, demographic processes and household dynamics in the Western Hemisphere. CIPEC seeks to contribute to an understanding of the human dimensions of global change by focusing on a set of interactions within a diverse but related set of environmental, institutional, demographic and socioeconomic settings in the Americas. CIPEC addresses these issues at multiple scales (from household to communities to regions) and across a variety of forest ecosystems (temperate deciduous, temperate rain, tropical dry, tropical moist and tropical rain forests) and institutional arrangements (communal tenure, private tenure, conservation for use, conservation for diversity). The research strategy integrates remotely sensed data with demographic census data, community and household surveys, and forest and soil mensuration.
To date work has begun at sites in Indiana, Mexico, Guatemala, Ecuador, Bolivia and Brazil. Additional sites in Honduras, Mexico, Brazil, Chile and other locations are foreseen.
When We Don't Know the Costs or the Benefits: Adaptive Strategies for Abating Climate Change
Michael Schlesinger
Most quantitative studies of climate-change policy attempt to predict the greenhouse-gas reduction plan that will have the optimum balance of long-term costs and benefits. We find that the large uncertainties associated with the climate-change problem can make the policy prescriptions of this traditional approach unreliable. In this study, we construct a large uncertainty space that includes the possibility of large and/or abrupt climate changes and/or of technology breakthroughs that radically reduce projected abatement costs. We use computational experiments on a linked system of climate and economic models to compare the performance of a simple adaptive strategy -- one that can make midcourse corrections based on observations of the climate and economic systems -- and two commonly advocated 'best-estimate' policies based on different expectations about the long-term consequences of climate change. We find that the 'Do-a-Little' and 'Emissions-Stabilization' best-estimate policies perform well in the respective regions of the uncertainty space where their estimates are valid, but can fail severely in those regions where their estimates are wrong. In contrast, the adaptive strategy can make midcourse corrections and avoid significant errors. While its success is no surprise, the adaptive-strategy approach provides an analytic framework to examine important policy and research issues that will likely arise as society adapts to climate change, and which cannot be easily addressed in studies using best-estimate approaches.
Climate Impacts and the Timing of Actions
Joel D. Scheraga,
The ultimate objective of the Framework Convention on Climate Change (FCCC) is "to achieve stabilization of greenhouse gas concentrations in the atmosphere at a level that would prevent dangerous anthropogenic interference with the climate system" (Article 2). Although the definition of "dangerous" is unresolved and an appropriate concentration target has yet to be identified, the intent of the FCCC is to protect human health and the environment, while preserving sustainable economic development.
One important consideration in meeting the objectives of the FCCC is how mitigation costs are likely to vary with the timing of emissions reductions and alternative pathways to different concentration targets. Earlier studies have tended to show that emissions time paths that initially involve modest reductions followed by sharper reductions later on are less expensive than those involving substantial reductions in the short-term (i.e., "acting later" is preferred to "acting sooner"). However, these studies have generally not examined the environmental consequences of selecting one emissions trajectory over another.
This study considers both costs and benefits of alternative emissions trajectories. Insights are gained about the timing of emissions reductions intended to achieve a given concentration target by considering a wide range of illustrative scenarios of environmental consequences. It is demonstrated that when the magnitude and timing of impacts are considered in addition to cost-effectiveness, it is preferable (based on a net benefit criterion) to increase initial emissions reductions relative to later reductions (i.e., "acting sooner" is preferred to "acting later"). This result is robust over a wide range of scenarios.
What can Political Scientists Contribute to an Understanding of Environmental Policy?
Robert O. Keohane, Duke UniversityThe basic contribution of political science to the understanding of environmental policy is to provide a positive view of the outcomes we observe in the real world, taking into account the strategies that individuals, organizations and states are likely to follow in pursuit of their own objectives. Political science complements natural science and economics in two major ways: first, it uses scientific assessments of physical effects and economic costs and benefits as a basis for a further analysis of incentives for human action, in view of power relations, interests, and prevailing ideas and institutions. Second, it helps us understand the scientific assessments themselves, in view of the social and political context in which they are embedded.
In this talk, Dr. Keohane will pay special attention to the question of how to understand the impact of scientific assessments of international environmental problems, and his illustrative focus will be the issue of climate change. For these purposes, an "assessment" will be defined as a document that presents itself as using scientific or technical knowledge in ways that have implications for policy or other behavior. The various Intergovernmental Panel on Climate Change (IPCC) reports constitute prominent examples of assessments.
Climate Change and Vector-Borne Diseases: Integration at Global and Microscopic Levels
Jonathan Patz
The United Nation's Intergovernmental Panel on Climate Change (IPCC) estimates an unprecedented global rise of 2.0#C by the year 2100. Of major concern is that these changes can affect the spread of many serious infectious diseases, including malaria and dengue fever.
Climate change would directly affect disease transmission by shifting the mosquito's geographic range, increasing reproductive and biting rates, and shortening pathogen incubation period. Human migration and damage to health infrastructures from the projected increase in climate variability and sea level rise could indirectly contribute to disease transmission.
We have used global scale mathematical modeling to study the impact of climate change on potential dengue transmission and have applied site-specific empirical analysis to improve predictions of malaria's response to climate influence. Results indicate that temperate regions become more suitable to dengue transmission, given viral introduction. The malaria study, showed significant differences in the mosquito interspecies responses to climate regarding biting rates. Also, higher mosquito infective potential was observed at warmer temperatures. Combined, these studies emphasize the importance of integrating new information from empirical studies into iterative mathematical models of climate change impacts.
Land Use /Cover Change: Issues for Integrated Assessment and the Social Sciences
Billie Lee Turner I
Land-use/cover change has been elevated to a major research position within the global environmental change and environment and development communities. It is fundamental to a large number of natural science issues, ranging from ecosystem fragmentation to biogeochemical cycling and potential climate warming. Regardless of the global issues, land-use/cover change is also fundamental to sustainability or sustainable development, with important implications for production and consumption. Finally, land-use/land cover change has become the center piece of international research explicitly attempting to link the social and natural sciences; neither cover or use can be understood adequately from either science perspective alone.The integrative qualities of land-use/cover change research have galvanized the "tweener" community those historically situated between the natural and social sciences. The social sciences at large, however, have been reluctant to embrace the integration, in part because (i) so much of the funding and donor community interests seem focused on those elements of the issue most relevant to the natural and remote sensing sciences and (ii) the social sciences at large have not embraced spatially explicit analysis of the kind, especially in integrative assessments and models. These two claims are explored, especially attempts to "socialize the pixel."
Global Land-Use Information: Integrating Traditional and Non-Traditional Sources
Elaine Matthews, NASACharacteristics of land-use systems, and their evolution over time, influence numerous aspects of exchanges of energy, water, nutrients, and greenhouse gases between the atmosphere and biosphere. However, understanding and modeling anthropogenic impacts on these spheres is hampered by the lack of current and historical information on global land-use systems and the mechanisms that drive them. Although profuse amounts of statistical land-use data are available from many sources, they have never been integrated globally to characterize the environments in which perturbations occur (spatial distribution) or to reconstruct the temporal sequences of disturbance in ways that are relevant to modeling impacts on climate or biogeochemical cycles.
This talk presents a project that takes advantage of the complementary strengths of several data sources by integrating thematically rich information with areally and historically precise inventories of land-cover change. These sources include historical LANDSAT studies of land-cover status in the humid tropics; disturbance indices developed from traditional maps; historical agricultural, forestry and census statistics; and existing global data on environment (vegetation, soils, climate) and human impact (human and livestock populations, irrigated rice cultivation, and nitrogenous fertilizer consumption).