Global Scenarios for Carbon Dioxide Emissions

The paper describes global scenarios for carbon dioxide emissions. They are based on the global scenarios formulated with the Global 2100 model and described in the book "Buying Greenhouse Insurance" by Manne and Richels. The input data used by Manne and Richels were modified to reflect scenario results of individual countries that contributed to the CHALLENGE network. Within CHALLENGE, researchers explore globally efficient measures to reduce the risk of adverse climate change. The approach used by the participants in these activities is to formulate reference scenarios for future carbon emissions. Any carbon mitigation is then measured relative to the reference case. With Global 2100, it is possible to quantify the effects of a hypothetical carbon tax on energy demand and supply. In the formulation of the model, this is equivalent to introducing all mitigation measures of which the specific costs are less than the tax. The main conclusion of the paper is that with costs of up to US$ 200 per ton of carbon, global energy related carbon dioxide emissions could be stabilized between 1990 and 2020

Learn-by-doing and Carbon Dioxide Abatement [Revised March 2002]

There are inherent difficulties in solving LBD(learn-by-doing) models. Basic to such models is the idea that the accumulation of experience leads to a lowering of costs. This paper is intended to explore some of the algorithmic issues in LBD modeling for carbon dioxide abatement. When using a standard algorithm for nonlinear programming, there is no guarantee that a local LBD optimum will also be a global optimum. Fortunately, despite the absence of guarantees, there is a good chance that one of the standard algorithms will produce a global optimum for models of this type. Moreover, there is a new procedure named BARON. In the case of small models, a global optimum can be recognized and guaranteed through BARON. Eventually, it should be possible for BARON or a similar approach to be extended top large-scale LBD models for climate change. Meanwhile, in order to check for local optima, the most practical course is to apply several different nonlinear programming algorithms - and several different starting solutions with each of them

Birds and people in Europe

At a regional scale, species richness and human population size are frequently positively correlated across space. Such patterns may arise because both species richness and human density increase with energy availability. If the species-energy relationship is generated through the 'more individuals' hypothesis, then the prediction is that areas with high human densities will also support greater numbers of individuals from other taxa. We use the unique data available for the breeding birds in Europe to test this prediction. Overall regional densities of bird species are higher in areas with more people; species of conservation concern exhibit the same pattern. Avian density also increases faster with human density than does avian biomass, indicating that areas with a higher human density have a higher proportion of small-bodied individuals. The analyses also underline the low numbers of breeding birds in Europe relative to humans, with a median of just three individual birds per person, and 4 g of bird for every kilogram of human

Moving Beyond Concentrations: The Challenge of Limiting Temperature Change

The UN Framework Convention on Climate Change shifted the attention of the policy community from stabilizing greenhouse gas emissions to stabilizing atmospheric greenhouse gas concentrations. While this represents a step forward, it does not go far enough. We find that, given the uncertainty in the climate system, focusing on atmospheric concentrations is likely to convey a false sense of precision. The causal chain between human activity and impacts is laden with uncertainty. From a benefit-cost perspective, it would be desirable to minimize the sum of mitigation costs and damages. Unfortunately, our ability to quantify and value impacts is limited. For the time being, we must rely on a surrogate. Focusing on temperature rather than on concentrations provides much more information on what constitutes an ample margin of safety. Concentrations mask too many uncertainties that are crucial for policy making.

Fast Structuring of Radio Networks for Multi-Message Communications

We introduce collision free layerings as a powerful way to structure radio networks. These layerings can replace hard-to-compute BFS-trees in many contexts while having an efficient randomized distributed construction. We demonstrate their versatility by using them to provide near optimal distributed algorithms for several multi-message communication primitives. Designing efficient communication primitives for radio networks has a rich history that began 25 years ago when Bar-Yehuda et al. introduced fast randomized algorithms for broadcasting and for constructing BFS-trees. Their BFS-tree construction time was $O(D \log^2 n)$ rounds, where $D$ is the network diameter and $n$ is the number of nodes. Since then, the complexity of a broadcast has been resolved to be $T_{BC} = \Theta(D \log \frac{n}{D} + \log^2 n)$ rounds. On the other hand, BFS-trees have been used as a crucial building block for many communication primitives and their construction time remained a bottleneck for these primitives. We introduce collision free layerings that can be used in place of BFS-trees and we give a randomized construction of these layerings that runs in nearly broadcast time, that is, w.h.p. in $T_{Lay} = O(D \log \frac{n}{D} + \log^{2+\epsilon} n)$ rounds for any constant $\epsilon>0$. We then use these layerings to obtain: (1) A randomized algorithm for gathering $k$ messages running w.h.p. in $O(T_{Lay} + k)$ rounds. (2) A randomized $k$-message broadcast algorithm running w.h.p. in $O(T_{Lay} + k \log n)$ rounds. These algorithms are optimal up to the small difference in the additive poly-logarithmic term between $T_{BC}$ and $T_{Lay}$. Moreover, they imply the first optimal $O(n \log n)$ round randomized gossip algorithm

Application of habitat thresholds in conservation: Considerations, limitations, and future directions

AbstractHabitat thresholds are often interpreted as the minimum required area of habitat, and subsequently promoted as conservation targets in natural resource policies and planning. Unfortunately, several recent reviews and messages of caution on the application of habitat thresholds in conservation have largely fallen on deaf ears, leading to a dangerous oversimplification and generalization of the concept. We highlight the prevalence of oversimplification/over-generalization of results from habitat threshold studies in policy documentation, the consequences of such over-generalization, and directions for habitat threshold studies that have conservation applications without risking overgeneralization. We argue that in order to steer away from misapplication of habitat thresholds in conservation, we should not focus on generalized nominal habitat values (i.e., amounts or percentages of habitat), but on the use of habitat threshold modeling for comparative exercises of area-sensitivity or the identification of environmental dangers. In addition, we should remain focused on understanding the processes and mechanisms underlying species responses to habitat change. Finally, studies could that focus on deriving nominal value threshold amounts should do so only if the thresholds are detailed, species-specific, and translated to conservation targets particular to the study area only

International Energy Workshop

Part I: Overview of Poll Responses Part II: Frequency Distributions Part III: Individual Poll Responses, "Busines-as-Usual" Cases Part IV: Individual Poll Resposnses, Carbon Emission Reduction Case

International Energy Workshop: A Progress Report

The International Energy Workshop (IEW) is a network of analysts concerned with international energy issues. It aims to compare long-term energy projections and to understand the reasons for diverging views. The IEW conducts iterative polling on key energy issues and publishes the results of these polls semiannually. The poll results are discussed at annual meetings, alternative between Europe and North America. Participation in the IEW is informal and is open to anyone supporting the goals of the Workshop. This report describes the status and progress of the IEW in mid-1987. It also summarizes the discussions from the meeting held at IIASA in June 1987