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Cafaro M.,University of Salento | Cafaro M.,Euro Mediterranean Center for Climate Change | Tempesta P.,Complutense University of Madrid
Concurrency Computation Practice and Experience | Year: 2011

We present a deterministic parallel algorithm for the k-majority problem, that can be used to find in parallel frequent items, i.e. those whose multiplicity is greater than a given threshold, and is therefore useful to process iceberg queries and in many other different contexts of applied mathematics and information theory. The algorithm can be used both in the online (stream) context and in the offline setting, the difference being that in the former case we are restricted to a single scan of the input elements, so that verifying the frequent items that have been determined is not allowed (e.g. network traffic streams passing through internet routers), while in the latter a parallel scan of the input can be used to determine the actual k-majority elements. To the best of our knowledge, this is the first parallel algorithm solving the proposed problem. Copyright © 2011 John Wiley & Sons, Ltd.

Jakob M.,Potsdam Institute for Climate Impact Research | Luderer G.,Potsdam Institute for Climate Impact Research | Steckel J.,Potsdam Institute for Climate Impact Research | Tavoni M.,Euro Mediterranean Center for Climate Change | Monjon S.,Center International Of Recherche Sur Lenvironnement Et Le Developpement
Climatic Change | Year: 2012

This paper compares the results of the three state of the art climate-energy-economy models IMACLIM-R, ReMIND-R, and WITCH to assess the costs of climate change mitigation in scenarios in which the implementation of a global climate agreement is delayed or major emitters decide to participate in the agreement at a later stage only. We find that for stabilizing atmospheric GHG concentrations at 450 ppm CO 2-only, postponing a global agreement to 2020 raises global mitigation costs by at least about half and a delay to 2030 renders ambitious climate targets infeasible to achieve. In the standard policy scenario-in which allocation of emission permits is aimed at equal per-capita levels in the year 2050-regions with above average emissions (such as the EU and the US alongside the rest of Annex-I countries) incur lower mitigation costs by taking early action, even if mitigation efforts in the rest of the world experience a delay. However, regions with low per-capita emissions which are net exporters of emission permits (such as India) can possibly benefit from higher future carbon prices resulting from a delay. We illustrate the economic mechanism behind these observations and analyze how (1) lock-in of carbon intensive infrastructure, (2) differences in global carbon prices, and (3) changes in reduction commitments resulting from delayed action influence mitigation costs. © 2011 Springer Science+Business Media B.V.

Luderer G.,Potsdam Institute for Climate Impact Research | DeCian E.,Euro Mediterranean Center for Climate Change | Hourcade J.-C.,Center International Of Recherche Sur Lenvironment Et Le Development | Leimbach M.,Potsdam Institute for Climate Impact Research | And 2 more authors.
Climatic Change | Year: 2012

This paper analyzes the regional distribution of climate change mitigation costs in a global cap-and-trade regime. Four stylized burden-sharing rules are considered, ranging from GDP-based permit allocations to schemes that foresee a long-term convergence of per-capita emission permits. The comparison of results from three structurally different hybrid, integrated energy-economy models allows us to derive robust insights as well as identify sources of uncertainty with respect to the regional distribution of the costs of climate change mitigation. We find that regional costs of climate change mitigation may deviate substantially from the global mean. For all models, the mitigation cost average of the four scenarios is higher for China than for the other macro-regions considered. Furthermore, China suffers above-world-average mitigation costs for most burden-sharing rules in the long-term. A decomposition of mitigation costs into (a) primary (domestic) abatement costs and (b) permit trade effects, reveals that the large uncertainty about the future development of carbon prices results in substantial uncertainties about the financial transfers associated with carbon trade for a given allocation scheme. This variation also implies large uncertainty about the regional distribution of climate policy costs. © 2012 Springer Science+Business Media B.V.

Storto A.,Norwegian Meteorological Institute | Storto A.,Euro Mediterranean Center for Climate Change | Randriamampianina R.,Norwegian Meteorological Institute
Journal of Geophysical Research: Atmospheres | Year: 2010

Statistical objective analysis requires the explicit specification of the observation and background error covariances. This paper deals with the estimation of the latter within a high-latitude regional model. Four different approaches have been adopted to simulate the error evolution in the analysis and forecast steps of the model: i) the largely-adopted NMC method, applied to both a winter and a summer season data set, ii) global ensemble analyses projected forward to the 6-hour forecast range by the limited-area model itself, iii) limited-area ensemble variational assimilation with unperturbed lateral boundary conditions (LBCs) and iv) limited-area ensemble variational assimilation with perturbed lateral boundary conditions. The structure of the four background error covariance matrices was extensively compared. It turned out that the NMC-derived standard deviations had stronger amplitude at the large scales, especially in the lower troposphere, compared to those derived using the ensemble technique, and much broader horizontal and large-scale vertical correlations. The contribution of lateral boundary perturbations is shown to be significant. Moreover, neglecting these LBCs perturbations contributes to unrealistic features, such as artificial small variances near the boundaries, which tend to spuriously propagate towards the inner area. Furthermore, humidity variances and associated cross-covariances tend to be weaker in the ensemble assimilation experiments, in particular when lateral boundary conditions are not perturbed. A one-month assimilation period allowed us to evaluate the impact of the different background error statistics on the forecasts: wind, geopotential and partly temperature are clearly benefiting from the use of ensemble-based background error covariances; humidity skill scores are noticeably improved when background error covariances from limited-area ensemble assimilation were used. The seasonality of the background error structures was also investigated, and it was found non-negligible for the performance of the data assimilation and forecast systems. © 2010 by the American Geophysical Union.

Tavoni M.,Euro Mediterranean Center for Climate Change | Tavoni M.,Fondazione Eni Enrico Mattei | de Cian E.,Euro Mediterranean Center for Climate Change | de Cian E.,Fondazione Eni Enrico Mattei | And 3 more authors.
Climatic Change | Year: 2012

This paper assesses the economic value associated with the development of various low-carbon technologies in the context of climate stabilization. We analyze the impact of restrictions on the development of specific mitigation technologies, comparing three integrated assessment models used in the RECIPE comparison exercise. Our results indicate that the diversification of the carbon mitigation portfolio is an important determinant of the feasibility of climate policy. Foregoing specific low carbon technologies raises the cost of achieving the climate policy, though at different rates. CCS and renewables are shown to have the highest value, given their flexibility and wide coverage. The costs associated with technology failure are shown to be related to the role that each technology plays in the stabilization scenario, but also to the expectations about their technological progress. In particular, the costs of restriction of mature technologies can be partly compensated by more innovation and technological advancement. © 2011 Springer Science+Business Media B.V.

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