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How to understand and reason about uncertainty in climate science is a topic that is receiving increasing attention in both the scientific and philosophical literature. This paper provides a perspective on exploring ways to understand, assess, and reason about uncertainty in climate science, including application to the Intergovernmental Panel on Climate Change (IPCC) assessment reports. Uncertainty associated with climate science and the science–policy interface presents unique challenges owing to the complexity of the climate system itself, the potential for adverse socioeconomic impacts of climate change, and the politicization of proposed policies to reduce societal vulnerability to climate change. The challenges to handling uncertainty at the science– policy interface are framed using the “monster” metaphor, whereby attempts to tame the monster are described. An uncertainty lexicon is provided that describes the natures and levels of uncertainty and ways of representing and reasoning about uncertainty. Uncertainty of climate models is interpreted in the context of model inadequacy, uncertainty in model parameter values, and initial condition uncertainty. This article examines the challenges of building confidence in climate models and, in particular, the issue of confidence in simulations of the twenty-first-century climate. The treatment of uncertainty in the IPCC assessment reports is examined, including the IPCC Fourth Assessment Report conclusion regarding the attribution of climate change in the latter half of the twentieth century. Ideas for monster-taming strategies are discussed for institutions, individual scientists, and communities.
How to understand and reason about uncertainty in climate science is a topic that is receiving increasing attention in both the scientific and philosophical literature. This paper provides a perspective on exploring ways to understand, assess, and reason about uncertainty in climate science, including application to the Intergovernmental Panel on Climate Change (IPCC) assessment reports. Uncertainty associated with climate science and the science–policy interface presents unique challenges owing to the complexity of the climate system itself, the potential for adverse socioeconomic impacts of climate change, and the politicization of proposed policies to reduce societal vulnerability to climate change. The challenges to handling uncertainty at the science– policy interface are framed using the “monster” metaphor, whereby attempts to tame the monster are described. An uncertainty lexicon is provided that describes the natures and levels of uncertainty and ways of representing and reasoning about uncertainty. Uncertainty of climate models is interpreted in the context of model inadequacy, uncertainty in model parameter values, and initial condition uncertainty. This article examines the challenges of building confidence in climate models and, in particular, the issue of confidence in simulations of the twenty-first-century climate. The treatment of uncertainty in the IPCC assessment reports is examined, including the IPCC Fourth Assessment Report conclusion regarding the attribution of climate change in the latter half of the twentieth century. Ideas for monster-taming strategies are discussed for institutions, individual scientists, and communities.
Abstract
A series of clouds-radiation experiments was carried out in June 1980 in Arctic stratus clouds occurring over the Beaufort Sea using the NCAR Electra aircraft. This paper is an analysis of the hemispheric radiation fields obtained with Eppley pyranometers and silicon flux detectors, and the cloud microphysical data obtained with the Knollenberg FSSP and 200X probes. These data were collected in a series of 12 vertical profiles in a variety of boundary layer stratus and altostratus situations. The results are interpreted with the aid of a theoretical radiative transfer model developed by Slingo and Schrecker.
The Knollenberg measurements indicated a wide range of cloud liquid water contents which generally increased from cloud base to cloud top. Values of the equivalent radius of the droplet size distribution are presented. Based on the agreement between the radiation measurements and the model calculations, it is concluded that the Knollenberg FSSP probe produced realistic liquid water concentrations in the present study.
Cloud reflectivity, transmissivity, and absorptivity were obtained with the Eppley pyranometers over the total solar spectrum, and also in the visible and near infrared regions, while the silicon detector produced values over the total spectrum, and in the near-infrared. The reflectivity and transmissivity obtained with the two systems agreed well with each other, and also with the model calculations. The measured values of absorptivity were systematically greater than those predicted, particularly in the visible region.
The theoretical model was used to investigate in each cloud profile the roles of aerosols, gaseous and droplet absorptions, and surface reflectivity. In particular, it was found that Arctic summer aerosol did not significantly affect the bulk radiative properties of the clouds, but did have a large effect on the ratio of diffuse to total radiation above the cloud.
Abstract
A series of clouds-radiation experiments was carried out in June 1980 in Arctic stratus clouds occurring over the Beaufort Sea using the NCAR Electra aircraft. This paper is an analysis of the hemispheric radiation fields obtained with Eppley pyranometers and silicon flux detectors, and the cloud microphysical data obtained with the Knollenberg FSSP and 200X probes. These data were collected in a series of 12 vertical profiles in a variety of boundary layer stratus and altostratus situations. The results are interpreted with the aid of a theoretical radiative transfer model developed by Slingo and Schrecker.
The Knollenberg measurements indicated a wide range of cloud liquid water contents which generally increased from cloud base to cloud top. Values of the equivalent radius of the droplet size distribution are presented. Based on the agreement between the radiation measurements and the model calculations, it is concluded that the Knollenberg FSSP probe produced realistic liquid water concentrations in the present study.
Cloud reflectivity, transmissivity, and absorptivity were obtained with the Eppley pyranometers over the total solar spectrum, and also in the visible and near infrared regions, while the silicon detector produced values over the total spectrum, and in the near-infrared. The reflectivity and transmissivity obtained with the two systems agreed well with each other, and also with the model calculations. The measured values of absorptivity were systematically greater than those predicted, particularly in the visible region.
The theoretical model was used to investigate in each cloud profile the roles of aerosols, gaseous and droplet absorptions, and surface reflectivity. In particular, it was found that Arctic summer aerosol did not significantly affect the bulk radiative properties of the clouds, but did have a large effect on the ratio of diffuse to total radiation above the cloud.
Abstract
Aircraft measurements of infrared radiation and cloud microphysics that were collected during the June 1980 Arctic Stratus Experiment are presented and analyzed with the aid of an infrared radiative transfer model. The radiation measurements were obtained with the NCAR Electra's Eppley pyrgeometers and a Barnes PRT-6 radiometer, and the cloud particle observations were obtained with the Knollenberg FSSP and 200X probes.
The data were used to derive values of cloud emittances, mass and volume absorption coefficients, cloud reflectances, cooling rates and radiative extinction lengths. These parameters were found to be strongly dependent on the cloud drop size distribution, and a parameterization of the absorption coefficient in terms of liquid water content and droplet equivalent radius is presented. The window reflectance of the clouds was determined to be between 6.4 and 8.8%.
Abstract
Aircraft measurements of infrared radiation and cloud microphysics that were collected during the June 1980 Arctic Stratus Experiment are presented and analyzed with the aid of an infrared radiative transfer model. The radiation measurements were obtained with the NCAR Electra's Eppley pyrgeometers and a Barnes PRT-6 radiometer, and the cloud particle observations were obtained with the Knollenberg FSSP and 200X probes.
The data were used to derive values of cloud emittances, mass and volume absorption coefficients, cloud reflectances, cooling rates and radiative extinction lengths. These parameters were found to be strongly dependent on the cloud drop size distribution, and a parameterization of the absorption coefficient in terms of liquid water content and droplet equivalent radius is presented. The window reflectance of the clouds was determined to be between 6.4 and 8.8%.
Abstract
The occurrence of cloudiness over the Beaufort Sea region of the Arctic Basin during June 1980, is related to the ambient large-scale meteorological conditions. Cloud data are obtained from a hand analysis of the visible and infrared Defense Meteorological Satellite Program (DMSP) images and from the U.S. Air Force Three-Dimensional Nephanalysis (3DNEPH). A comparison of the two cloud cover datasets showed good agreement for mid- and high-level cloudiness, but low-level cloudiness was significantly underestimated by the 3DNEPH. The study therefore uses a composite data set consisting of the 3DNEPH data at mid- and upper-levels, and the DMSP data at lower levels. Atmospheric data are obtained from the European Centre for Medium-Range Weather Forecasts (ECMWF) objective analysis, and large-scale heat and moisture budgets are constructed. The budgets are used to investigate the processes which contribute to relative humidity changes.
The budgets are related to the cloud cover for both the monthly cloudiness values averaged over the entire region, and for the twice-daily grid point values. Large amounts of low cloud cover during June are attributed primarily to the low level advection of moisture and a residual cooling due to radiation and boundary layer turbulence. The occurrence of midlevel cloudiness is associated with the large-scale transport of heat and moisture. Several relative humidity-based parameterizations currently used in GCMs were tested for their ability to diagnose June 1980 conditions in the Arctic using the initialized fields, but their performance was generally poor. The addition of other atmospheric parameters and budget terms in the empirical formulae provided some improvement, although the agreement with observations remained limited. While our results are dependent upon the quality of the atmospheric and cloud data in this region, they provide further examples of the deficiencies of simple diagnostic layered-cloud parameterizations.
Abstract
The occurrence of cloudiness over the Beaufort Sea region of the Arctic Basin during June 1980, is related to the ambient large-scale meteorological conditions. Cloud data are obtained from a hand analysis of the visible and infrared Defense Meteorological Satellite Program (DMSP) images and from the U.S. Air Force Three-Dimensional Nephanalysis (3DNEPH). A comparison of the two cloud cover datasets showed good agreement for mid- and high-level cloudiness, but low-level cloudiness was significantly underestimated by the 3DNEPH. The study therefore uses a composite data set consisting of the 3DNEPH data at mid- and upper-levels, and the DMSP data at lower levels. Atmospheric data are obtained from the European Centre for Medium-Range Weather Forecasts (ECMWF) objective analysis, and large-scale heat and moisture budgets are constructed. The budgets are used to investigate the processes which contribute to relative humidity changes.
The budgets are related to the cloud cover for both the monthly cloudiness values averaged over the entire region, and for the twice-daily grid point values. Large amounts of low cloud cover during June are attributed primarily to the low level advection of moisture and a residual cooling due to radiation and boundary layer turbulence. The occurrence of midlevel cloudiness is associated with the large-scale transport of heat and moisture. Several relative humidity-based parameterizations currently used in GCMs were tested for their ability to diagnose June 1980 conditions in the Arctic using the initialized fields, but their performance was generally poor. The addition of other atmospheric parameters and budget terms in the empirical formulae provided some improvement, although the agreement with observations remained limited. While our results are dependent upon the quality of the atmospheric and cloud data in this region, they provide further examples of the deficiencies of simple diagnostic layered-cloud parameterizations.
Abstract
Realistic treatment of sea ice processes in general circulation models is needed to simulate properly global climate and climate change scenarios. As new sea ice treatments become available, it is necessary to evaluate them in terms of their accuracy and computational time. Here, several dynamic ice models are compared using both a 2-category and 28-category ice thickness distribution. Simulations are conducted under normal wind forcing, as well as under increased and decreased wind speeds. It is found that the lack of a shear strength parameterization in the cavitating fluid rheology produces significantly different results in both ice thickness and ice velocity than those produced by an elliptical rheology. Furthermore, use of a 28-category ice thickness distribution amplifies differences in the responses of the various models. While the choice of dynamic model is governed by requirements of accuracy and implementation, it appears that, in terms of both parameterization of physical properties and computational time, the elliptical rheology is well-suited for inclusion in a GCM.
Abstract
Realistic treatment of sea ice processes in general circulation models is needed to simulate properly global climate and climate change scenarios. As new sea ice treatments become available, it is necessary to evaluate them in terms of their accuracy and computational time. Here, several dynamic ice models are compared using both a 2-category and 28-category ice thickness distribution. Simulations are conducted under normal wind forcing, as well as under increased and decreased wind speeds. It is found that the lack of a shear strength parameterization in the cavitating fluid rheology produces significantly different results in both ice thickness and ice velocity than those produced by an elliptical rheology. Furthermore, use of a 28-category ice thickness distribution amplifies differences in the responses of the various models. While the choice of dynamic model is governed by requirements of accuracy and implementation, it appears that, in terms of both parameterization of physical properties and computational time, the elliptical rheology is well-suited for inclusion in a GCM.
The 2005 Atlantic hurricane season was the most active and costly season on record. Recent publications linking an increase in hurricane intensity to increasing tropical sea surface temperatures have fueled the debate on whether or not global warming is causing an increase in hurricane intensity. Because of the substantial implications of the hurricane–global warming issue for society and the immediate policy relevance associated with decision making related to Hurricane Katrina, attacks and rebuttals related to this research are being made in the media and on the World Wide Web without the rigor or accountability expected of scientific discourse. In this paper, we aim to promote a balanced and thoughtful examination of this subject by
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clarifying the debate surrounding the subject as to whether or not global warming is causing an increase in global hurricane intensity,
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illustrating a methodology of hypothesis testing to address multiple criticisms of a complex hypothesis that involves a causal chain, and
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providing a case study of the impact of politics, the media, and the World Wide Web on the scientific process.
The 2005 Atlantic hurricane season was the most active and costly season on record. Recent publications linking an increase in hurricane intensity to increasing tropical sea surface temperatures have fueled the debate on whether or not global warming is causing an increase in hurricane intensity. Because of the substantial implications of the hurricane–global warming issue for society and the immediate policy relevance associated with decision making related to Hurricane Katrina, attacks and rebuttals related to this research are being made in the media and on the World Wide Web without the rigor or accountability expected of scientific discourse. In this paper, we aim to promote a balanced and thoughtful examination of this subject by
-
clarifying the debate surrounding the subject as to whether or not global warming is causing an increase in global hurricane intensity,
-
illustrating a methodology of hypothesis testing to address multiple criticisms of a complex hypothesis that involves a causal chain, and
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providing a case study of the impact of politics, the media, and the World Wide Web on the scientific process.
Warming of the arctic climate is having a substantial impact on the Alaskan North Slope coastal region. The warming is associated with increasing amounts of open water in the arctic seas, rising sea level, and thawing permafrost. Coastal geography and increasing development along the coastline are contributing to increased vulnerability of infrastructure, utilities, and supplies of food and gasoline to storms, flooding, and coastal erosion. Secondary impacts of coastal flooding may include harm to animals and their land or sea habitats, if pollutants are released. Further, Inupiat subsistence harvesting of marine sources of food, offshore resource extraction, and marine transportation may be affected. This paper describes a project to understand, support, and enhance the local decision-making process on the North Slope of Alaska on socioeconomic issues that are influenced by warming, climate variability, and extreme weather events.
Warming of the arctic climate is having a substantial impact on the Alaskan North Slope coastal region. The warming is associated with increasing amounts of open water in the arctic seas, rising sea level, and thawing permafrost. Coastal geography and increasing development along the coastline are contributing to increased vulnerability of infrastructure, utilities, and supplies of food and gasoline to storms, flooding, and coastal erosion. Secondary impacts of coastal flooding may include harm to animals and their land or sea habitats, if pollutants are released. Further, Inupiat subsistence harvesting of marine sources of food, offshore resource extraction, and marine transportation may be affected. This paper describes a project to understand, support, and enhance the local decision-making process on the North Slope of Alaska on socioeconomic issues that are influenced by warming, climate variability, and extreme weather events.
Abstract
Satellite retrievals of surface evaporation and precipitation from the Hamburg Ocean Atmosphere Parameters and Fluxes from Satellite Data (HOAPS-3) dataset are used to document the distribution of evaporation, precipitation, and freshwater flux over the Mediterranean and Black Seas. An analysis is provided of the major scales of temporal and spatial variability of the freshwater budget and the atmospheric processes responsible for the water flux changes. The satellite evaporation fluxes are compared with fields from three different reanalysis datasets [40-yr ECMWF Re-Analysis (ERA-40), ERA-Interim, and NCEP].
The results show a water deficit in the Mediterranean region that averages to about 2.4 mm day−1 but with a significant east–west asymmetry ranging from 3.5 mm day−1 in the eastern part to about 1.1 mm day−1 in the western part of the basin. The zonal asymmetry in the water deficit is driven by evaporation differences that are in turn determined by variability in the air–sea humidity difference in the different parts of the Mediterranean basin. The Black Sea freshwater deficit is 0.5 mm day−1, with maxima off the northern coast (0.9 mm day−1) that are attributed to both evaporation maxima and precipitation minima there.
The trend analysis of the freshwater budget shows that the freshwater deficit increases in the 1988–2005 period. The prominent increase in the eastern part of the basin is present in the satellite and all three reanalysis datasets. The water deficit is due to increases in evaporation driven by increasing sea surface temperature, while precipitation does not show any consistent trends in the period. Similarly, in the Black Sea, trends in the freshwater deficit are mainly due to evaporation, although year-to-year variability is due to precipitation patterns.
Abstract
Satellite retrievals of surface evaporation and precipitation from the Hamburg Ocean Atmosphere Parameters and Fluxes from Satellite Data (HOAPS-3) dataset are used to document the distribution of evaporation, precipitation, and freshwater flux over the Mediterranean and Black Seas. An analysis is provided of the major scales of temporal and spatial variability of the freshwater budget and the atmospheric processes responsible for the water flux changes. The satellite evaporation fluxes are compared with fields from three different reanalysis datasets [40-yr ECMWF Re-Analysis (ERA-40), ERA-Interim, and NCEP].
The results show a water deficit in the Mediterranean region that averages to about 2.4 mm day−1 but with a significant east–west asymmetry ranging from 3.5 mm day−1 in the eastern part to about 1.1 mm day−1 in the western part of the basin. The zonal asymmetry in the water deficit is driven by evaporation differences that are in turn determined by variability in the air–sea humidity difference in the different parts of the Mediterranean basin. The Black Sea freshwater deficit is 0.5 mm day−1, with maxima off the northern coast (0.9 mm day−1) that are attributed to both evaporation maxima and precipitation minima there.
The trend analysis of the freshwater budget shows that the freshwater deficit increases in the 1988–2005 period. The prominent increase in the eastern part of the basin is present in the satellite and all three reanalysis datasets. The water deficit is due to increases in evaporation driven by increasing sea surface temperature, while precipitation does not show any consistent trends in the period. Similarly, in the Black Sea, trends in the freshwater deficit are mainly due to evaporation, although year-to-year variability is due to precipitation patterns.
Abstract
Recent work suggests that there may exist skill in forecasting tropical cyclones (TC) using dynamically based ensemble products, such as those obtained from the ECMWF Monthly Forecast System (ECMFS). The ECMFS features an ensemble of 51 coupled ocean–atmosphere simulations integrated to 32 days once per week. Predicted levels of TC activity in the North Atlantic Ocean with these monthly ensemble forecasts is compared with the observed variability during the months of June–October during 2008 and 2009. Results indicate that the forecast system can capture large-scale regions that have a higher or lower risk of TC activity and that it has skill above climatology for the Gulf of Mexico and the “Main Development Region” on intraseasonal time scales. Regional forecast skill is traced to the model’s ability to capture the large-scale evolution of deep-layer vertical shear, the frequency of easterly waves, and the variance in 850-hPa relative vorticity. The predictability of TC activity, along with the forecast utility of the ECMFS, is shown to be sensitive to the phase and intensity of the Madden–Julian oscillation at the time of model initialization.
Abstract
Recent work suggests that there may exist skill in forecasting tropical cyclones (TC) using dynamically based ensemble products, such as those obtained from the ECMWF Monthly Forecast System (ECMFS). The ECMFS features an ensemble of 51 coupled ocean–atmosphere simulations integrated to 32 days once per week. Predicted levels of TC activity in the North Atlantic Ocean with these monthly ensemble forecasts is compared with the observed variability during the months of June–October during 2008 and 2009. Results indicate that the forecast system can capture large-scale regions that have a higher or lower risk of TC activity and that it has skill above climatology for the Gulf of Mexico and the “Main Development Region” on intraseasonal time scales. Regional forecast skill is traced to the model’s ability to capture the large-scale evolution of deep-layer vertical shear, the frequency of easterly waves, and the variance in 850-hPa relative vorticity. The predictability of TC activity, along with the forecast utility of the ECMFS, is shown to be sensitive to the phase and intensity of the Madden–Julian oscillation at the time of model initialization.
