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Laffineur T.,National School of Meteorological Studies | Laffineur T.,Ecole Polytechnique - Palaiseau | Claud C.,Ecole Polytechnique - Palaiseau | Chaboureau J.-P.,CNRS Laboratory for Aerology | And 2 more authors.
Monthly Weather Review | Year: 2014

Polar lows are intense high-latitude mesocyclones that form during the cold season over open sea. Their relatively small-scale and short life span lead to a rather poor representation in model outputs and meteorological reanalyses. In this paper, the ability of the Interim European Centre for Medium-Range Weather Forecasts (ECMWF) Re-Analysis (ERA-Interim) to represent polar lows over the Norwegian and Barents Sea is assessed, and a comparison with the 40-yr ECMWF Re-Analysis (ERA-40) is provided for three cold seasons (1999-2000 until 2001-02). A better representation in ERA-Interim is found, with 13 systems captured out of the 29 observed, against 6 in the case of ERA-40. Reasons for the lack of representation are identified. Unexpectedly, the representation of different polar low sizes does not appear to be linked to the resolution. Rather, it is the representation of synoptic conditions that appears to be essential. In a second part, a downscaling is conducted using the mesoscale model Méso-NH. For each observed polar low, a pair of simulations is performed: one initialized by ERA-Interim and the other one by ERA-40. An improvement is noted with 22 polar lows represented when ERA-Interim is used. Through a model-to-satellite approach, it is shown that even if polar lows are simulated, convective processes remain insufficiently represented. Wind speeds, which were underestimated in reanalyses, are nevertheless more realistic in the Méso-NH simulations. These results are supported by a spectral analysis of reanalyses and Méso-NH fields. © 2014 American Meteorological Society.


Kriegler E.,Potsdam Institute for Climate Impact Research | O'Neill B.C.,U.S. National Center for Atmospheric Research | Hallegatte S.,National School of Meteorological Studies | Kram T.,PBL Netherlands Environmental Assessment Agency | And 3 more authors.
Global Environmental Change | Year: 2012

Socio-economic scenarios constitute an important tool for exploring the long-term consequences of anthropogenic climate change and available response options. A more consistent use of socio-economic scenarios that would allow an integrated perspective on mitigation, adaptation and residual climate impacts remains a major challenge. We assert that the identification of a set of global narratives and socio-economic pathways offering scalability to different regional contexts, a reasonable coverage of key socio-economic dimensions and relevant futures, and a sophisticated approach to separating climate policy from counter-factual " no policy" scenarios would be an important step toward meeting this challenge. To this end, we introduce the concept of " shared socio-economic (reference) pathways" Sufficient coverage of the relevant socio-economic dimensions may be achieved by locating the pathways along the dimensions of challenges to mitigation and to adaptation. The pathways should be specified in an iterative manner and with close collaboration between integrated assessment modelers and impact, adaptation and vulnerability researchers to assure coverage of key dimensions, sufficient scalability and widespread adoption. They can be used not only as inputs to analyses, but also to collect the results of different climate change analyses in a matrix defined by two dimensions: climate exposure as characterized by a radiative forcing or temperature level and socio-economic development as classified by the pathways. For some applications, socio-economic pathways may have to be augmented by " shared climate policy assumptions" capturing global components of climate policies that some studies may require as inputs. We conclude that the development of shared socio-economic (reference) pathways, and integrated socio-economic scenarios more broadly, is a useful focal point for collaborative efforts between integrated assessment and impact, adaptation and vulnerability researchers. © 2012 Elsevier Ltd.


Guivarch C.,Center International de Recherche sur lEnvironnement et le Developpement | Hallegatte S.,Center International de Recherche sur lEnvironnement et le Developpement | Hallegatte S.,National School of Meteorological Studies
Global Environmental Change | Year: 2013

Political attention has increasingly focused on limiting warming to 2 °C. However, there is no consensus on both questions "Is the 2 °C target achievable?" and "What should be done with this target that becomes increasingly difficult to achieve?" This paper aims at disentangling the points of deep uncertainty underlying this absence on consensus. It first gives simple visualizations of the challenge posed by the 2 °C target and shows how key assumptions (on the points of deep uncertainty) influence the answer to the target achievability question. It then proposes an "uncertainties and decisions tree", linking different beliefs on climate change, the achievability of different policies, and current international policy dynamics to various options to move forward on climate change. © 2012 Elsevier Ltd.


Hallegatte S.,Center International de Recherche sur lEnvironnement et le Developpement | Hallegatte S.,National School of Meteorological Studies | Henriet F.,Organisation for Economic Co-operation and Development | Corfee-Morlot J.,Organisation for Economic Co-operation and Development
Climatic Change | Year: 2011

Cities are particularly vulnerable to climate change and climate extremes in part because they concentrate many activities, people and wealth in limited areas. As a result they represent an important scale for assessment and understanding of climate change impacts. This paper provides a conceptual and methodological framework for urban economic impact assessment of climate change. The focus of the paper is on model-based analysis of future scenarios, including a framing of uncertainty for these projections, as one valuable input into the decision-making process. The paper highlights the main assessment difficulties, methods and tools, and selected examples across these areas. A number of challenges are unique to climate change impact assessment and others are unique to the problem of working at local scales. The paper also identifies the need for additional research, including the need for more integrated and systemic approaches to address climate change as a part of the urban development challenge as well as the need to assess the economic impacts of climate change and response policy at local scale. © 2010 Springer Science+Business Media B.V.


Guivarch C.,Center International de Recherche sur lEnvironnement et le Developpement | Hallegatte S.,Center International de Recherche sur lEnvironnement et le Developpement | Hallegatte S.,National School of Meteorological Studies
Climatic Change | Year: 2011

To clarify the link between existing infrastructure legacy and the 2°C target, we extend the work of Davis et al. (Science 329:1330-1333, 2010) by introducing non-CO2 greenhouse gases and the inertia in transportation-needs drivers. We conclude that climate policies able to maintain climate change below 2°C cannot disregard existing infrastructure. © 2011 Springer Science+Business Media B.V.


Viguie V.,CIRAD - Agricultural Research for Development | Hallegatte S.,The World Bank | Hallegatte S.,National School of Meteorological Studies
Nature Climate Change | Year: 2012

Cities are at the forefront of climate policies. However, urban climate policies are not implemented in a vacuum; they interact with other policy goals, such as economic competitiveness or social issues. These interactions can lead to trade-offs and implementation obstacles, or to synergies. Little analysis investigating these interactions exists, in part because it requires a broad interdisciplinary approach. Using a new integrated city model, we provide a first quantification of these trade-offs and synergies, going beyond the qualitative statements that have been published so far. We undertake a multicriteria analysis of three urban policies: a greenbelt policy, a zoning policy to reduce flood risk and a transportation subsidy. Separately, each of these policies seems to be undesirable because each one negatively affects at least one of the different policy goals; however, in a policy mix, the consequences of each policy are not simply additive. This nonlinearity permits building policy combinations that are win-win strategies. In particular, flood zoning and greenbelt policies can only be accepted if combined with transportation policies. Our results show that stand-alone adaptation and mitigation policies are unlikely to be politically acceptable and emphasize the need to mainstream climate policy within urban planning. © 2012 Macmillan Publishers Limited. All rights reserved.


Notaro M.,University of Wisconsin - Madison | Mauss A.,National School of Meteorological Studies | Williams J.W.,University of Wisconsin - Madison
Ecological Applications | Year: 2012

This study focuses on potential impacts of 21st century climate change on vegetation in the Southwest United States, based on debiased and interpolated climate projections from 17 global climate models used in the Fourth Assessment Report of the Intergovernmental Panel on Climate Change. Among these models a warming trend is universal, but projected changes in precipitation vary in sign and magnitude. Two independent methods are applied: a dynamic global vegetation model to assess changes in plant functional types and bioclimatic envelope modeling to assess changes in individual tree and shrub species and biodiversity. The former approach investigates broad responses of plant functional types to climate change, while considering competition, disturbances, and carbon fertilization, while the latter approach focuses on the response of individual plant species, and net biodiversity, to climate change. The dynamic model simulates a region-wide reduction in vegetation cover during the 21st century, with a partial replacement of evergreen trees with grasses in the mountains of Colorado and Utah, except at the highest elevations, where tree cover increases. Across southern Arizona, central New Mexico, and eastern Colorado, grass cover declines, in some cases abruptly. Due to the prevalent warming trend among all 17 climate models, vegetation cover declines in the 21st century, with the greatest vegetation losses associated with models that project a drying trend. The inclusion of the carbon fertilization effect largely ameliorates the projected vegetation loss. Based on bioclimatic envelope modeling for the 21st century, the number of tree and shrub species that are expected to experience robust declines in range likely outweighs the number of species that are expected to expand in range. Dramatic shifts in plant species richness are projected, with declines in the high-elevation evergreen forests, increases in the eastern New Mexico prairies, and a northward shift of the Sonoran Desert biodiversity maximum. © 2012 by the Ecological Society of America.


Pre-monsoon is a very challenging period for regional duty-forecasters and those involved in mitigation of severe weather consequences. Indeed, violent thunderstorms producing high winds, large hail and even tornados are common features from March to May in East India and Bangladesh. Taking advantage of SAARC (South Asian Association for Regional Cooperation) research publications, as well as knowledge and practical methodology developed by NOAA's National Weather Service in the Tornado Alley, a methodology is proposed that might help IMD forecasters make the best use of their new workstation SYNERGIE. The case study of the 13 April 2010 severe storm has been chosen for this purpose. More than 140 reported deaths and nearly 500,000 people were left homeless or otherwise affected by the storm. A good comprehension of both synoptic and mesoscale conceptual models is needed; then, aided by appropriate numerical model fields, drawing proper weather symbols on surface analysis charts is an important step towards the building and sharing of local expertise with regional or local forecasters. A graphical analysis is proposed and discussed.


Corfee-Morlot J.,Organisation for Economic Co-operation and Development | Cochran I.,MINES ParisTech | Hallegatte S.,National School of Meteorological Studies | Teasdale P.-J.,Organisation for Economic Co-operation and Development
Climatic Change | Year: 2011

Despite a flurry of activity in cities on climate change and growing interest in the research community, climate policy at city-scale remains fragmented and basic tools to facilitate good decision-making are lacking. This paper draws on an interdisciplinary literature review to establish a multilevel risk governance conceptual framework. It situates the local adaptation policy challenge and action within this to explore a range of institutional questions associated with strengthening local adaptation and related functions of local government. It highlights the value of institutional design to include analytic-deliberative practice, focusing on one possible key tool to support local decision-making-that of boundary organizations to facilitate local science-policy assessment. After exploring a number of examples of boundary organisations in place today, the authors conclude that a number of institutional models are valid. A common feature across the different approaches is the establishment of a science-policy competence through active deliberation and shared analysis engaging experts and decision-makers in an iterative exchange of information. Important features that vary include the geographic scope of operation and the origin of funding, the level and form of engagement of different actors, and the relationship with "producers" of scientific information. National and sub-national (regional) governments may play a key role to provide financial and technical assistance to support the creation of such boundary organizations with an explicit mandate to operate at local levels; in turn, in a number of instances boundary organizations have been shown to be able to facilitate local partnerships, engagement and decision-making on adaptation. While the agenda for multi-level governance of climate change is inevitably much broader than this, first steps by national governments to work with sub-national governments, urban authorities and other stakeholders to advance capacity in this area could be an important step for local adaptation policy agenda. © 2010 Springer Science+Business Media B.V.


Hallegatte S.,National School of Meteorological Studies
Environmental Research Letters | Year: 2012

This article reviews the channels through which sea level rise can affect economic growth, namely the loss of land, the loss of infrastructure and physical capital, the loss of social capital, the additional cost from extreme events and coastal floods, and the increased expenditure for coastal protection. It discusses how existing studies on the direct impact of sea level rise could be used to investigate the resulting consequences on economic growth, emphasizes research needs on this question, and discusses consequences on migration. © 2012 IOP Publishing Ltd.

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