Página 1 dos resultados de 106 itens digitais encontrados em 0.015 segundos

Early warning signals of Atlantic Meridional Overturning Circulation collapse in a fully coupled climate model

Boulton, Chris A.; Allison, Lesley C.; Lenton, Timothy M.
Fonte: Nature Pub. Group Publicador: Nature Pub. Group
Tipo: Artigo de Revista Científica
Publicado em 08/12/2014 EN
Relevância na Pesquisa
55.89%
The Atlantic Meridional Overturning Circulation (AMOC) exhibits two stable states in models of varying complexity. Shifts between alternative AMOC states are thought to have played a role in past abrupt climate changes, but the proximity of the climate system to a threshold for future AMOC collapse is unknown. Generic early warning signals of critical slowing down before AMOC collapse have been found in climate models of low and intermediate complexity. Here we show that early warning signals of AMOC collapse are present in a fully coupled atmosphere-ocean general circulation model, subject to a freshwater hosing experiment. The statistical significance of signals of increasing lag-1 autocorrelation and variance vary with latitude. They give up to 250 years warning before AMOC collapse, after ~550 years of monitoring. Future work is needed to clarify suggested dynamical mechanisms driving critical slowing down as the AMOC collapse is approached.

Nonnormal Thermohaline Circulation Dynamics in a Coupled Ocean–Atmosphere GCM

Tziperman, Eli; Zanna, Laure; Penland, Cecile
Fonte: American Meteorological Society Publicador: American Meteorological Society
Tipo: Artigo de Revista Científica
EN_US
Relevância na Pesquisa
56.19%
Using the GFDL coupled atmosphere–ocean general circulation model CM2.1, the transient amplification of thermohaline circulation (THC) anomalies due to its nonnormal dynamics is studied. A reduced space based on empirical orthogonal functions (EOFs) of temperature and salinity anomaly fields in the North Atlantic is constructed. Under the assumption that the dynamics of this reduced space is linear, the propagator of the system is then evaluated and the transient growth of THC anomalies analyzed. Although the linear dynamics are stable, such that any initial perturbation eventually decays, nonnormal effects are found to result in a significant transient growth of temperature, salinity, and THC anomalies. The growth time scale for these anomalies is between 5 and 10 yr, providing an estimate of the predictability time of the North Atlantic THC in this model. There are indications that these results are merely a lower bound on the nonnormality of THC dynamics in the present coupled GCM. This seems to suggest that such nonnormal effects should be seriously considered if the predictability of the THC is to be quantitatively evaluated from models or observations. The methodology presented here may be used to produce initial perturbations to the ocean state that may result in a stricter estimate of ocean and THC predictability than the common procedure of initializing with an identical ocean state and a perturbed atmosphere.; Earth and Planetary Sciences

The Effect of Milankovitch Variations in Insolation on Equatorial Seasonality

Ashkenazy, Yosef; Eisenman, Ian; Gildor, Hezi; Tziperman, Eli
Fonte: American Meteorological Society Publicador: American Meteorological Society
Tipo: Artigo de Revista Científica
EN_US
Relevância na Pesquisa
65.89%
Although the sun crosses the equator 2 times per year at the equinoxes, at times in the past the equatorial insolation has had only one maximum and one minimum throughout the seasonal cycle because of Milankovitch orbital variations. Here a state-of-the-art coupled atmosphere–ocean general circulation model is used to study the effect of such insolation forcing on equatorial surface properties, including air and sea temperature, salinity, winds, and currents. It is shown that the equatorial seasonality is altered according to the insolation with, for example, either maximum sea surface temperature (SST) close to the vernal equinox and minimum SST close to the autumnal equinox or vice versa. The results may have important implications for understanding tropical climate as well as for the interpretation of proxy data collected from equatorial regions.; Earth and Planetary Sciences

12.800 Fluid Dynamics of the Atmosphere and Ocean, Fall 2003; Fluid Dynamics of the Atmosphere and Ocean

Hansen, James A.
Fonte: MIT - Massachusetts Institute of Technology Publicador: MIT - Massachusetts Institute of Technology
EN-US
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56.19%
This class introduces fluid dynamics to first year graduate students. The aim is to help students acquire an understanding of some of the basic concepts of fluid dynamics that will be needed as a foundation for advanced courses in atmospheric science, physical oceanography, ocean engineering, etc. The emphasis will be on fluid fundamentals, but with an atmosphere/ocean twist.

Assessment of the Impacts of Climate Change on Mountain Hydrology : Development of a Methodology through a Case Study in the Andes of Peru

Vergara, Walter; Deeb, Alejandro; Leino, Irene; Kitoh, Akio; Escobar, Marisa
Fonte: World Bank Publicador: World Bank
Relevância na Pesquisa
46.14%
The objective of study of the impacts of climate change on mountain hydrology is to develop a methodology to assess the net impacts of climate change on the hydrological response in mountainous regions. This is done through a case study in the Peruvian Andes. There are few examples of predictions of the impact of climate change on resource availability and even fewer examples of the applications of such predictions to planning for sustainable economic development. This report presents a summary of the efforts of a Bank energy and climate change team to develop methodological tools for the assessment of climate impacts on surface hydrology in the Peruvian Andes. The importance of analyzing the potential climate impacts on hydrology in Peru arises in part from concerns about the retreat of tropical glaciers, the drying of unique Andean wetland ecosystems, as well as increased weather variability and weather extremes, all of which will affect water regulation. The study, together with a recently published report by the World Bank...

Social Impacts of Climate Change in Peru : A District Level Analysis of the Effects of Recent and Future Climate Change on Human Development and Inequality

Andersen, Lykke E.; Suxo, Addy; Verner, Dorte
Fonte: Banco Mundial Publicador: Banco Mundial
Relevância na Pesquisa
56.02%
This paper uses district level data to estimate the general relationship between climate, income and life expectancy in Peru. The analysis finds that both incomes and life expectancy show hump-shaped relationships, with optimal average annual temperatures around 18-20ºC. These estimated relationships were used to simulate the likely effects of both past (1958-2008) and future (2008-2058) climate change. At the aggregate level, future climate change in Peru is estimated to cause a small reduction in average life expectancy of about 0.2 years. This average, however, hides much larger losses in the already hot areas as well as substantial gains in currently cold areas. Similarly, the average impact on incomes is a modest reduction of 2.3 percent, but with some districts experiencing losses of up to 20 percent and others gains of up to 13 percent. Future climate change is estimated to cause an increase in poverty (all other things equal), but to have no significant effect on the distribution of incomes.

Ethiopia - A Country Study on the Economic Impacts of Climate Change

World Bank
Fonte: Washington, DC Publicador: Washington, DC
Relevância na Pesquisa
56%
It is now widely recognized that low-income countries in tropical and sub-tropical regions will be disproportionally affected by the adverse impacts of climate change. The combination of already fragile environments, dominance of climate-sensitive sectors in economic activity, and low autonomous adaptive capacity in these regions implies a high vulnerability to the harmful effects of global warming on agricultural production and food security, water resources, human health, physical infrastructure and ecosystems. Recent authoritative scientific assessments emphasize that, even under the most optimistic assumptions about the success of future global mitigation action, an acceleration of adaptation efforts in developing countries over the next decades is essential to build resilience and reduce damage costs. The effects of climate change vary across countries, and adaptation and coping capabilities are influenced by geographical, economic, cultural and political factors. Successful adaptation programs must therefore take into account country-specific circumstances. This pilot study aims to develop a methodology that provides an economy-wide framework for analyzing economic impacts from climate change and potential adaptation policies that developing countries might undertake in the near and long term. To accomplish this objective...

Municipal Vulnerability to Climate Change and Climate-Related Events in Mexico

Borja-Vega, Christian; de la Fuente, Alejandro
Fonte: World Bank, Washington, DC Publicador: World Bank, Washington, DC
EN_US
Relevância na Pesquisa
46.16%
A climate change vulnerability index in agriculture is presented at the municipal level in Mexico. Because the index is built with a multidimensional approach to vulnerability (exposure, sensitivity and adaptive capacity), it represents a tool for policy makers, academics and government alike to inform decisions about climate change resilience and regional variations within the country. The index entails baseline (2005) and prediction (2045) levels based on historic climate data and future-climate modeling. The results of the analysis suggest a wide variation in municipal vulnerability across the country at baseline and prediction points. The vulnerability index shows that highly vulnerable municipalities demonstrate higher climate extremes, which increases uncertainty for harvest periods, and for agricultural yields and outputs. The index shows at baseline that coastal areas host some of the most vulnerable municipalities to climate change in Mexico. However, it also shows that the Northwest and Central regions will likely experience the largest shifts in vulnerability between 2005 and 2045. Finally...

Social Impacts of Climate Change in Chile : A Municipal Level Analysis of the Effects of Recent and Future Climate Change on Human Development and Inequality

Andersen, Lykke E.; Verner, Dorte
Fonte: World Bank, Washington, DC Publicador: World Bank, Washington, DC
EN_US
Relevância na Pesquisa
55.89%
This paper uses municipality level data to estimate the general relationship between climate, income, and life expectancy in Chile. The analysis finds that incomes are negatively related to temperature, while life expectancy is not significantly related to average temperatures. Both incomes and life expectancy are greater in areas with either very little rain or a lot of rain. The authors use the estimated relationships to simulate the effects of both past (1958-08) and future (2008-58) climate change. The findings indicate that past climate change has been favorable for the central, and most populous, part of Chile, and it has contributed to reduced poverty and reduced inequality of health outcomes. Whereas temperatures in the past have shown a downward trend for most of the Chilean population, climate models suggest that they will increase in the future, and that there will be a reduction in precipitation in the central part of Chile. The analysis simulates the likely effects of these projected climate changes over the next 50 years. The findings suggest that expected future climate will tend to reduce incomes across the whole country...

Multi-model climate projections for biodiversity risk assessments

Fordham, D.; Wigley, T.; Brook, B.
Fonte: Ecological Soc Amer Publicador: Ecological Soc Amer
Tipo: Artigo de Revista Científica
Publicado em //2011 EN
Relevância na Pesquisa
86.12%
Species distribution models, linked to climate projections, are widely used in extinction-risk assessment and conservation planning. However, the degree of confidence that we can place on future climate-change projections depends on global climate-model performance and involves uncertainties that need to be assessed rigorously via climate-model evaluation. Performance assessments are important because the choice of climate model influences projections of species’ range movement and extinction risk. A consensus view from the climate modeling community is that no single climate model is superior in its ability to forecast key climatic features. Despite this, the advantages of using multi-model ensemble averaged climate forecasts to account for climate-model uncertainties have not been recognized by ecologists. Here we propose a method to use a range of skill and convergence metrics to rank commonly used atmosphere–ocean general circulation models (AOGCMs) according to their skill in reproducing 20-year observed patterns of regional and global climates of interest, and to assess their consistency with other AOGCMs. By eliminating poorly performing models and averaging the remainder with equal weights, we show how downscaled annual multi-climate-model ensemble-averaged forecasts...

Emulating coupled atmosphere-ocean and carbon cycle models with a simpler model, MAGICC6 - Part 1: Model description and calibration

Meinshausen, M.; Raper, S.; Wigley, T.
Fonte: European Geophysical Society Publicador: European Geophysical Society
Tipo: Artigo de Revista Científica
Publicado em //2011 EN
Relevância na Pesquisa
66.01%
Current scientific knowledge on the future response of the climate system to human-induced perturbations is comprehensively captured by various model intercomparison efforts. In the preparation of the Fourth Assessment Report (AR4) of the Intergovernmental Panel on Climate Change (IPCC), intercomparisons were organized for atmosphere-ocean general circulation models (AOGCMs) and carbon cycle models, named “CMIP3” and “C⁴MIP”, respectively. Despite their tremendous value for the scientific community and policy makers alike, there are some difficulties in interpreting the results. For example, radiative forcings were not standardized across the various AOGCM integrations and carbon cycle runs, and, in some models, key forcings were omitted. Furthermore, the AOGCM analysis of plausible emissions pathways was restricted to only three SRES scenarios. This study attempts to address these issues. We present an updated version of MAGICC, the simple carbon cycle-climate model used in past IPCC Assessment Reports with enhanced representation of time-varying climate sensitivities, carbon cycle feedbacks, aerosol forcings and ocean heat uptake characteristics. This new version, MAGICC6, is successfully calibrated against the higher complexity AOGCMs and carbon cycle models. Parameterizations of MAGICC6 are provided. The mean of the emulations presented here using MAGICC6 deviates from the mean AOGCM responses by only 2.2% on average for the SRES scenarios. This enhanced emulation skill in comparison to previous calibrations is primarily due to: making a “like-with-like comparison” using AOGCM-specific subsets of forcings; employing a new calibration procedure; as well as the fact that the updated simple climate model can now successfully emulate some of the climate-state dependent effective climate sensitivities of AOGCMs. The diagnosed effective climate sensitivity at the time of CO₂ doubling for the AOGCMs is on average 2.88°C...

Uncertainty in modeled upper ocean heat content change

Tokmakian, Robin; Challenor, Peter
Fonte: Springer Publicador: Springer
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
56.05%
The article of record as published may be located at http://dx.doi.org/10.1007/s00382-013-1709-9; This paper examines the uncertainty in the change in the heat content in the ocean component of a general circulation model. We describe the design and implementation of our statistical methodology. Using an ensemble of model runs and an emulator, we produce an estimate of the full probability distribution function (PDF) for the change in upper ocean heat in an Atmosphere/ Ocean General Circulation Model, the Community Climate System Model v. 3, across a multi-dimensional input space. We show how the emulator of the GCM’s heat content change and hence, the PDF, can be validated and how implausible outcomes from the emulator can be identified when compared to observational estimates of the metric. In addition, the paper describes how the emulator outcomes and related uncertainty information might inform estimates of the same metric from a multi-model Coupled Model Intercomparison Project phase 3 ensemble.

Emulating coupled atmosphere-ocean and carbon cycle models with a simpler model, MAGICC6 - Part 2: Applications

Meinshausen, M.; Raper, S.; Wigley, T.
Fonte: European Geophysical Society Publicador: European Geophysical Society
Tipo: Artigo de Revista Científica
Publicado em //2011 EN
Relevância na Pesquisa
65.94%
Intercomparisons of coupled atmosphere-ocean general circulation models (AOGCMs) and carbon cycle models are important for galvanizing our current scientific knowledge to project future climate. Interpreting such intercomparisons faces major challenges, not least because different models have been forced with different sets of forcing agents. Here, we show how an emulation approach with MAGICC6 can address such problems. In a companion paper (Meinshausen et al., 2011a), we show how the lower complexity carbon cycle-climate model MAGICC6 can be calibrated to emulate, with considerable accuracy, globally aggregated characteristics of these more complex models. Building on that, we examine here the Coupled Model Intercomparison Project's Phase 3 results (CMIP3). If forcing agents missed by individual AOGCMs in CMIP3 are considered, this reduces ensemble average temperature change from pre-industrial times to 2100 under SRES A1B by 0.4 degree(s)C. Differences in the results from the 1980 to 1999 base period (as reported in IPCC AR4) to 2100 are negligible, however, although there are some differences in the trajectories over the 21st century. In a second part of this study, we consider the new RCP scenarios that are to be investigated under the forthcoming CMIP5 intercomparison for the IPCC Fifth Assessment Report. For the highest scenario...

Agreeing on Robust Decisions : New Processes for Decision Making under Deep Uncertainty

Kalra, Nidhi; Hallegatte, Stephane; Lempert, Robert; Brown, Casey; Fozzard, Adrian; Gill, Stuart; Shah, Ankur
Fonte: World Bank, Washington, DC Publicador: World Bank, Washington, DC
Tipo: Publications & Research :: Policy Research Working Paper; Publications & Research
ENGLISH; EN_US
Relevância na Pesquisa
55.89%
Investment decision making is already difficult for any diverse group of actors with different priorities and views. But the presence of deep uncertainties linked to climate change and other future conditions further challenges decision making by questioning the robustness of all purportedly optimal solutions. While decision makers can continue to use the decision metrics they have used in the past (such as net present value), alternative methodologies can improve decision processes, especially those that lead with analysis and end in agreement on decisions. Such "Agree-on-Decision" methods start by stress-testing options under a wide range of plausible conditions, without requiring us to agree ex ante on which conditions are more or less likely, and against a set of objectives or success metrics, without requiring us to agree ex ante on how to aggregate or weight them. As a result, these methods are easier to apply to contexts of large uncertainty or disagreement on values and objectives. This inverted process promotes consensus around better decisions and can help in managing uncertainty. Analyses performed in this way let decision makers make the decision and inform them on (1) the conditions under which an option or project is vulnerable; (2) the tradeoffs between robustness and cost...

Climate Impacts on Energy Systems : Key Issues for Energy Sector Adaptation

Ebinger, Jane; Vergara, Walter
Fonte: World Bank Publicador: World Bank
Tipo: Publications & Research :: Publication; Publications & Research :: Publication
ENGLISH
Relevância na Pesquisa
46.21%
This report presents an overview of how the energy sector might be impacted by climate change and what options exist for its management. It focuses on energy sector adaptation, rather than mitigation, which has been a key focus of the energy sector and is not discussed in this report. This report draws on available scientific and peer-reviewed literature in the public domain and takes the perspective of the developing world to the extent possible. It starts with a discussion about observed and projected climate change (out to 2100), exploring trends, extremes, and 'hotspots'- geographic regions that will see significant changes or variability for relevant parameters (for example, temperature, runoff , and sea level rise). It then discusses what is known about the impacts of these changes on energy resources, infrastructure, and transportation systems as well as demand. It discusses what technologies or services are more vulnerable and identifies gaps in information or knowledge. The report concludes with a number of proposed near-term actions to foster dialogue...

Adjusting to policy expectations in climate change modeling : an interdiciplinary study of flux adjustments in coupled atmosphere-ocean general circulation models

Fonte: MIT Joint Program on the Science and Policy of Global Change Publicador: MIT Joint Program on the Science and Policy of Global Change
Formato: 36 p.; 242742 bytes; application/pdf
ENG
Relevância na Pesquisa
86.06%
This paper surveys and interprets the attitudes of scientists to the use of flux adjustments in climate projections with coupled Atmosphere Ocean General Circulation Models. The survey is based largely on the responses of 19 climate modellers to several questions and a discussion document circulated in 1995. We interpret the responses in terms of the following factors: the implicit assumptions which scientists hold about how the environmental policy process deals with scientific uncertainty over human-related global warming; the different scientific styles that exist in climate research; and the influence of organisations, institutions, and policy upon research agendas. We find evidence that scientists' perceptions of the policy process do play a role in shaping their scientific practices. In particular, many of our respondents expressed a preference for keeping discussion of the issue of flux adjustments within the climate modeling community, apparently fearing that climate contrarians would exploit the issue in the public domain. While this may be true, we point to the risk that such an approach may backfire. We also identify assumptions and cultural commitments lying at a deeper level which play at least as important a role as perceptions of the policy process in shaping scientific practices. This leads us to identify two groups of scientists...

Ocean–Cloud–Atmosphere–Land Interactions in the Southeastern Pacific: The VOCALS Program

Yuter, S. E.; Wood, R.; Weller, R.; McWilliams, J.; Zuidema, P.; Farrar, J. T.; De Szoeke, S. P.; Garreaud Salazar, René Darío; Clarke, A. D.; Feingold, G.; Coe, H.; Grados, C.; Bretherton, C. S.; Fairall, C.; Mechoso, C. R.
Fonte: American Meteorological Society Publicador: American Meteorological Society
Tipo: Artículo de revista
EN
Relevância na Pesquisa
56.13%
Artículo de publicación ISI; The present paper describes the Variability of the American Monsoon Systems (VAMOS) Ocean–Cloud–Atmosphere–Land Study (VOCALS), an international research program focused on the improved understanding and modeling of the southeastern Pacific (SEP) climate system on diurnal to interannual time scales. In the framework of the SEP climate, VOCALS has two fundamental objectives: 1) improved simulations by coupled atmosphere–ocean general circulation models (CGCMs), with an emphasis on reducing systematic errors in the region; and 2) improved estimates of the indirect effects of aerosols on low clouds and climate, with an emphasis on the more precise quantification of those effects. VOCALS major scientific activities are outlined, and selected achievements are highlighted. Activities described include monitoring in the region, a large international field campaign (the VOCALS Regional Experiment), and two model assessments. The program has already produced significant advances in the understanding of major issues in the SEP: the coastal circulation and the diurnal cycle, the ocean heat budget, factors controlling precipitation and formation of pockets of open cells in stratocumulus decks, aerosol impacts on clouds...

A global hybrid coupled model based on Atmosphere-SST feedbacks

Cimatoribus, Andrea A.; Drijfhout, Sybren S.; Dijkstra, Henk A.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
46.22%
A global hybrid coupled model is developed, with the aim of studying the effects of ocean-atmosphere feedbacks on the stability of the Atlantic meridional overturning circulation. The model includes a global ocean general circulation model and a statistical atmosphere model. The statistical atmosphere model is based on linear regressions of data from a fully coupled climate model on sea surface temperature both locally and hemispherically averaged, being the footprint of Atlantic meridional overturning variability. It provides dynamic boundary conditions to the ocean model for heat, freshwater and wind-stress. A basic but consistent representation of ocean-atmosphere feedbacks is captured in the hybrid coupled model and it is more than ten times faster than the fully coupled climate model. The hybrid coupled model reaches a steady state with a climate close to the one of the fully coupled climate model, and the two models also have a similar response (collapse) of the Atlantic meridional overturning circulation to a freshwater hosing applied in the northern North Atlantic.; Comment: The final publication is available at springerlink.com

Volcanic forcing improves Atmosphere-Ocean Coupled General Circulation Model scaling performance

Vyushin, Dmitry; Zhidkov, Igor; Havlin, Shlomo; Bunde, Armin; Brenner, Stephen
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 28/01/2004
Relevância na Pesquisa
46.15%
Recent Atmosphere-Ocean Coupled General Circulation Model (AOGCM) simulations of the twentieth century climate, which account for anthropogenic and natural forcings, make it possible to study the origin of long-term temperature correlations found in the observed records. We study ensemble experiments performed with the NCAR PCM for 10 different historical scenarios, including no forcings, greenhouse gas, sulfate aerosol, ozone, solar, volcanic forcing and various combinations, such as it natural, anthropogenic and all forcings. We compare the scaling exponents characterizing the long-term correlations of the observed and simulated model data for 16 representative land stations and 16 sites in the Atlantic Ocean for these scenarios. We find that inclusion of volcanic forcing in the AOGCM considerably improves the PCM scaling behavior. The scenarios containing volcanic forcing are able to reproduce quite well the observed scaling exponents for the land with exponents around 0.65 independent of the station distance from the ocean. For the Atlantic Ocean, scenarios with the volcanic forcing slightly underestimate the observed persistence exhibiting an average exponent 0.74 instead of 0.85 for reconstructed data.; Comment: 4 figures

Impact of Climate Drift on Twenty-First-Century Projection in a Coupled Atmospheric–Ocean General Circulation Model

Liang, Mao-Chang; Lin, Li-Ching; Tung, Ka-Kit; Yung, Yuk L.; Sun, Shan
Fonte: American Meteorological Society Publicador: American Meteorological Society
Tipo: Article; PeerReviewed Formato: application/pdf
Publicado em /10/2013
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76.07%
Reducing climate drift in coupled atmosphere–ocean general circulation models (AOGCMs) usually requires 1000–2000 years of spinup, which has not been practical for every modeling group to do. For the purpose of evaluating the impact of climate drift, the authors have performed a multimillennium-long control run of the Goddard Institute for Space Studies model (GISS-EH) AOGCM and produced different twentieth-century historical simulations and subsequent twenty-first-century projections by branching off the control run at various stages of equilibration. The control run for this model is considered at quasi equilibration after a 1200-yr spinup from a cold start. The simulations that branched off different points after 1200 years are robust, in the sense that their ensemble means all produce the same future projection of warming, both in the global mean and in spatial detail. These robust projections differ from the one that was originally submitted to the Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment Report (AR4), which branched off a not-yet-equilibrated control run. The authors test various common postprocessing schemes in removing climate drift caused by a not-yet-equilibrated ocean initial state and find them to be ineffective...