Extending and Implementing the Self-adaptive Virtual Processor for Distributed Memory Architectures

Many-core architectures of the future are likely to have distributed memory organizations and need fine grained concurrency management to be used effectively. The Self-adaptive Virtual Processor (SVP) is an abstract concurrent programming model which can provide this, but the model and its current implementations assume a single address space shared memory. We investigate and extend SVP to handle distributed environments, and discuss a prototype SVP implementation which transparently supports execution on heterogeneous distributed memory clusters over TCP/IP connections, while retaining the original SVP programming model

INFINITE UNCERTAINTY, FORGOTTEN FEEDBACKS, AND COST-BENEFIT ANALYSIS OF CLIMATE POLICY

Tol (2003) found evidence that the uncertainty that surrounds estimates of the marginal damage of climate change may be infinite even if total damages are finite and questioned the applicability of expected cost-benefit analysis to global mitigation policy. Yohe (2003) suggested that this problem could be alleviated if international development aid were directed at eliminating the source of the problem – climate induced negative growth rates in a few regions along a handful of troublesome scenarios. The hypothesis about adding a second policy lever to the climate policy calculus is shown to hold, but not as robustly as perhaps expected. Infinite uncertainty and its implications for global mitigation policy can be avoided for a reasonable price in the relatively unlikely event that climate change can cause negative economic growth in a region or two when the portfolio of international policies includes at least two tools.climate policy, development aid, equity weighting, expected cost-benefit analysis

THE WEAKEST LINK HYPOTHESIS FOR ADAPTIVE CAPACITY: AN EMPIRICAL TEST

Yohe and Tol (2001) built an indexing method for vulnerability based on the hypothesis that the adaptive capacity for any system facing a vector of external stresses could be explained by the weakest of eight underlying determinants – the so-called “weakest link” hypothesis. Subsequent work supported the hypothesis by analogy from other contexts, but we now offer perhaps the first attempt to explore its validity through empirical means. We estimate a structural form designed to accommodate the full range of possible interactions across determinants. The perfect complement case of the pure “weakest-link” formulation lies on one extreme, and the perfect substitute case where each determinant can compensate for all others at constant rates is the other limiting case. For vulnerability to natural disasters, infant mortality and drinking water treatment, we find qualified support for a modified weakest link hypothesis: the weakest indicator plays an important role, but is not essential because other factors can compensate (with increasing difficulty). For life expectancy, sanitation and nutrition, we find a relationship that is close to linear – the perfect substitute case where the various determinants of adaptive capacity can compensate for each other. Moreover, we find another source of diversity in the assessment of vulnerability, since the factors from which systems draw to create adaptive capacity are different for different risks.Adaptive capacity, vulnerability, weakest-link hypothesis, substitution

PRECAUTION AND A DISMAL THEOREM: IMPLICATIONS FOR CLIMATE POLICY AND CLIMATE RESEARCH

We discuss the implication of Weitzman's Dismal Theorem for climate policy and climate research.climate change, uncertainty

INFINITE UNCERTAINTY, FORGOTTEN FEEDBACKS, AND COST-BENEFIT ANALYSIS OF CLIMATE POLICY

Tol (2003) found evidence that the uncertainty that surrounds estimates of the marginal damage of climate change may be infinite even if total damages are finite and questioned the applicability of expected cost-benefit analysis to global mitigation policy. Yohe (2003) suggested that this problem could be alleviated if international development aid were directed at eliminating the source of the problem – climate induced negative growth rates in a few regions along a handful of troublesome scenarios. The hypothesis about adding a second policy lever to the climate policy calculus is shown to hold, but not as robustly as perhaps expected. Infinite uncertainty and its implications for global mitigation policy can be avoided for a reasonable price in the relatively unlikely event that climate change can cause negative economic growth in a region or two when the portfolio of international policies includes at least two tools.climate policy, development aid, equity weighting, expected cost-benefit analysis

THE WEAKEST LINK HYPOTHESIS FOR ADAPTIVE CAPACITY: AN EMPIRICAL TEST

Yohe and Tol (2001) built an indexing method for vulnerability based on the hypothesis that the adaptive capacity for any system facing a vector of external stresses could be explained by the weakest of eight underlying determinants – the so-called “weakest link” hypothesis. Subsequent work supported the hypothesis by analogy from other contexts, but we now offer perhaps the first attempt to explore its validity through empirical means. We estimate a structural form designed to accommodate the full range of possible interactions across determinants. The perfect complement case of the pure “weakest-link” formulation lies on one extreme, and the perfect substitute case where each determinant can compensate for all others at constant rates is the other limiting case. For vulnerability to natural disasters, infant mortality and drinking water treatment, we find qualified support for a modified weakest link hypothesis: the weakest indicator plays an important role, but is not essential because other factors can compensate (with increasing difficulty). For life expectancy, sanitation and nutrition, we find a relationship that is close to linear – the perfect substitute case where the various determinants of adaptive capacity can compensate for each other. Moreover, we find another source of diversity in the assessment of vulnerability, since the factors from which systems draw to create adaptive capacity are different for different risks.Adaptive capacity, vulnerability, weakest-link hypothesis, substitution

On Setting Near-term Climate Policy while the Dust Begins to Settle: The Legacy of the Stern Review

We review the explosion of commentary that has followed the release of the Stern Review: The Economics of Climate Change, and agree with most of what has been written. The Review is right when it argues on economic grounds for immediate intervention to reduce emissions of greenhouse gases, but we feel that it is right for the wrong reasons. A persuasive case can be made that climate risks are real and increasingly threatening. If follows that some sort of policy will be required, and the least cost approach necessarily involves starting now. Since policy implemented in 2007 will not “solve” the climate problem, near term interventions can be designed to begin the process by working to avoid locking in high carbon investments and providing adequate incentives for carbon sequestration. We argue that both objectives can be achieved without undue economic harm in the near term by pricing carbon at something on the order of $15 per ton as long as it is understood that the price will increase persistently and predictably at something like the rate of interest; and we express support for a tax alternative to the usual cap-and-trade approach.Stern Review, climate change, climate policy, social discount rate; risk and equity aversion

INFECTIOUS DISEASE, DEVELOPMENT, AND CLIMATE CHANGE: A SCENARIO ANALYSIS

We study the effects of development and climate change on infectious disease in Sub-Saharan Africa. Infant mortality and infectious disease are close related, but there are better data for the former. In an international cross-section, per capita income, literacy, and absolute poverty significantly affect infant mortality. We use scenarios of these three determinants, and of climate change to project the future incidence of malaria, assuming it to change proportionally to infant mortality. Malaria deaths will first increase, because of population growth and climate change, but then fall, because of development. This pattern is robust to the choice of scenario, parameters, and starting conditions; and it holds for diarrhoea, schistosomiasis, and dengue fever as well. However, the time and level of the mortality peak is very sensitive to assumptions. Climate change is important in the medium term, but dominated in the long term by development. As climate can only be changed with a substantial delay, development is the preferred strategy to reduced infectious diseases, even if that is exacerbated by climate change.Development, infectious disease, climate change, Sub-Saharan Africa, malaria

UNDERSTANDING LONG-TERM ENERGY USE AND CARBON DIOXIDE EMISSIONS IN THE USA

We compile a database of energy uses, energy sources, and carbon dioxide emissions for the USA for the period 1850-2002. We use a model to extrapolate the missing observations on energy use by sector. Overall emission intensity rose between 1850 and 1917, and fell between 1917 and 2002. The leading cause for the rise in emission intensity was the switch from wood to coal, but population growth, economic growth, and electrification contributed as well. After 1917, population growth, economic growth and electrification pushed emissions up further, and there was no net shift from fossil to non-fossil energy sources. From 1850 to 2002, emissions were reduced by technological and behavioural change (particularly in transport, manufacturing and households), structural change in the economy, and a shift from coal to oil and gas. These trends are stronger than electrification, explaining the fall in emissions relative to GDP.Carbon dioxide emissions, decomposition, environmental Kuznets curve, USA, history

Theory of evaporative cooling with energy-dependent elastic scattering cross section and application to metastable helium

The kinetic theory of evaporative cooling developed by Luiten et al. [Phys. Rev. A 53, 381 (1996)] is extended to include the dependence of the elastic scattering cross section on collision energy. We introduce a simple approximation by which the transition range between the low-temperature limit and the unitarity limit is described as well. Applying the modified theory to our measurements on evaporative cooling of metastable helium we find a scattering length |a| = 10(5) nm