142 results on '"Jeffrey T. Kiehl"'
Search Results
2. Global Changes in Terrestrial Vegetation and Continental Climate During the Paleocene‐Eocene Thermal Maximum
- Author
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Vera A. Korasidis, Scott L. Wing, Christine A. Shields, and Jeffrey T. Kiehl
- Subjects
Atmospheric Science ,Paleontology ,Oceanography - Published
- 2022
3. Systemic swings in end-Permian climate from Siberian Traps carbon and sulfur outgassing
- Author
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Christine A. Shields, Ryan R. Neely, Charles G. Bardeen, Jean-Francois Lamarque, Benjamin A. Black, Linda T. Elkins-Tanton, Jeffrey T. Kiehl, and Michael J. Mills
- Subjects
Extinction event ,010504 meteorology & atmospheric sciences ,Siberian Traps ,Global warming ,Ocean current ,010502 geochemistry & geophysics ,Atmospheric sciences ,01 natural sciences ,Ozone depletion ,Greenhouse gas ,Flood basalt ,General Earth and Planetary Sciences ,Global cooling ,0105 earth and related environmental sciences - Abstract
Siberian Traps flood basalt magmatism coincided with the end-Permian mass extinction approximately 252 million years ago. Proposed links between magmatism and ecological catastrophe include global warming, global cooling, ozone depletion and changes in ocean chemistry. However, the critical combinations of environmental changes responsible for global mass extinction are undetermined. In particular, the combined and competing climate effects of sulfur and carbon outgassing remain to be quantified. Here we present results from global climate model simulations of flood basalt outgassing that account for sulfur chemistry and aerosol microphysics with coupled atmosphere and ocean circulation. We consider the effects of sulfur and carbon in isolation and in tandem. We find that coupling with the ocean strongly influences the climate response to prolonged flood basalt-scale outgassing. We suggest that sulfur and carbon emissions from the Siberian Traps combined to generate systemic swings in temperature, ocean circulation and hydrology within a longer-term trend towards a greenhouse world in the early Triassic. Carbon and sulfur release from the Siberian Traps igneous province caused climate swings during the end-Permian mass extinction, according to coupled global climate simulations.
- Published
- 2018
4. Engaging the Green Man, breaking our spell of enchantment
- Author
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Jeffrey T. Kiehl
- Subjects
Aesthetics ,media_common.quotation_subject ,Spell ,Art ,media_common - Published
- 2020
5. A Tale of Two Cultures
- Author
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Jeffrey T. Kiehl
- Published
- 2020
6. FLUSHING THE SYSTEM: COUPLING LITHIUM ISOTOPES AND CLIMATE MODEL OBSERVATIONS DURING THE PETM
- Author
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Jeffrey T. Kiehl, James C Zachos, Phillip Pogge von Strandmann, William Rush, and Christine A. Shields
- Subjects
Coupling (electronics) ,Materials science ,Chemical physics ,Isotopes of lithium ,medicine ,Flushing ,Climate model ,medicine.symptom - Published
- 2020
7. CHANGES IN HYDROLOGY AND SEDIMENTATION DURING THE PALEOCENE-EOCENE THERMAL MAXIMUM IN THE SALISBURY EMBAYMENT, USA
- Author
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Christine A. Shields, Jeffrey T. Kiehl, James C Zachos, and William Rush
- Subjects
Hydrology ,Hydrology (agriculture) ,Carbon isotope excursion ,Sedimentation ,Geology - Published
- 2020
8. Monsoonal precipitation in the Paleo-Tethys warm pool during the latest Permian
- Author
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Jeffrey T. Kiehl and Christine A. Shields
- Subjects
Monsoon of South Asia ,010504 meteorology & atmospheric sciences ,Ocean current ,Paleontology ,Forcing (mathematics) ,010502 geochemistry & geophysics ,Oceanography ,Monsoon ,01 natural sciences ,Sea surface temperature ,Climatology ,Tropical monsoon climate ,Community Climate System Model ,Precipitation ,Ecology, Evolution, Behavior and Systematics ,Geology ,0105 earth and related environmental sciences ,Earth-Surface Processes - Abstract
Simulations of the late Permian (251 Ma) are analyzed with respect to the northern hemispheric Pangean monsoon. We find that the presence and spatial distribution of the warm pool, and not land-sea temperature differences, are the primary forcing agents for the monsoon. The land-sea temperature gradient, as a monsoonal mechanism, is tested by eliminating the Cathyasian peninsula and is found to have little impact on the spatial character of the monsoon. Furthermore, the response of the monsoon to the warm pool was tested by removing all Paleo-Tethys equatorial islands, which allows the warm pool to expand and migrate westward thus shifting the pattern of monsoonal precipitation. Given that paleogeography changes through time, these results have important implications for the migration and strength of the tropical monsoon over geologic time. Additionally, different CO2 regimes are presented, in which a 10-fold change in forcing produces diverging climates and therefore different warm pool and monsoon locales. Tropical and equatorial ocean currents impact the seasonal progression and location of the warm pool and atmospheric mass flux for the monsoonal regime is characterized and shown to change with warm pool movement. Experiments were conducted using the low-resolution version of Community Climate System Model, Version 3 (CCSM3) in both coupled and fixed sea surface temperature (SST) context. For validation purposes, a modern control is briefly presented with observations and is shown to represent both the spatial and seasonal progression of the Indian monsoon.
- Published
- 2018
9. Simulated changes to tropical cyclones across the Paleocene-Eocene Thermal Maximum (PETM) boundary
- Author
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Christine A. Shields, Jeffrey T. Kiehl, Colin M. Zarzycki, and Mathew Rothstein
- Subjects
Orbital forcing ,Paleontology ,Storm ,Atmospheric model ,Forcing (mathematics) ,Oceanography ,Climatology ,Wind shear ,Common spatial pattern ,Atmospheric electricity ,Tropical cyclone ,Ecology, Evolution, Behavior and Systematics ,Geology ,Earth-Surface Processes - Abstract
Tropical cyclones are an important meteorological and climatological process in Earth's climate system. These intense, localized storms mainly form over warm equatorial oceans, and propagate poleward. During their lifetime, tropical cyclones can strengthen leading to intense winds and rainfall events. These storms also carry moist energy that contribute to the poleward transport of atmospheric energy. Presently, concern exists about how the characteristics of tropical cyclones will change in a future warming world. The Paleocene Eocene Thermal Maximum (PETM) was a time in Earth's deep past in which the planet warmed by 5° - 8 °C due to an increase in atmospheric CO2. It is thus of interest to understand how past warming affected tropical cyclone behavior. Here, a high resolution (25 km) atmospheric model is used to study changes in tropical cyclones across the PETM boundary. Orbital variation is also investigated as an additional forcing mechanism at the time of the PETM. The climate simulations indicate that greenhouse forcing leads to a poleward shift in TCs, much like projected future scenarios and in simulations of other warm periods in Earth history. It is also found that the orbital forcing response is very different than the greenhouse cases due to the difference in thermal response, which, in turn, induces a different dynamical response in wind shear. Although the spatial pattern between changes across the PETM and the future differ, there are still many similarities in TC response for these two very different periods in time, indicating the robustness of the TC response to greenhouse warming.
- Published
- 2021
10. Increased frequency of extreme precipitation events in the North Atlantic during the PETM: Observations and theory
- Author
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Jeffrey T. Kiehl, Christine A. Shields, James C Zachos, and William Rush
- Subjects
010506 paleontology ,Paleontology ,Magnitude (mathematics) ,Forcing (mathematics) ,010502 geochemistry & geophysics ,Oceanography ,01 natural sciences ,Climatology ,Greenhouse gas ,Extratropical cyclone ,Climate model ,Sedimentary rock ,Precipitation ,Water cycle ,Ecology, Evolution, Behavior and Systematics ,Geology ,0105 earth and related environmental sciences ,Earth-Surface Processes - Abstract
Climate model simulations of the PETM (Paleocene-Eocene Thermal Maximum) warming have mainly focused on replicating the global thermal response through greenhouse forcing, i.e. CO2, at levels compatible with observations. Comparatively less effort has gone into assessing the skill of models to replicate the response of the hydrologic cycle to the warming, particularly on regional scales. Here we have assembled proxy records of regional precipitation, focusing on the Mid-Atlantic Coasts of North America (New Jersey) and Europe (Spain) to test the response of the hydrologic system to greenhouse gas forcing of the magnitude estimated for the PETM (i.e., 2×). Given evidence that the PETM initiated during a maximum in eccentricity, this includes the response under neutral and extreme orbital configurations. Modeled results show excellent agreement with observations in Northern Spain, with a significant increase in both mean annual and extreme precipitation resulting from increased CO2 levels under a neutral orbit. The Mid Atlantic Coast simulations agree with observations showing increases in both overall and extreme precipitation as a result of CO2 increases. In particular, the development of sustained atmospheric rivers might be significantly contributing to the extremes of the eastern Atlantic, whereas extratropical cyclones are likely contributing to the extremes in the western Atlantic. With an eccentric orbit that maximizes insolation during boreal summer, there is a suppression of extreme precipitation events in the eastern Atlantic and an amplification in the western Atlantic, which may account for observations in the relative timing of the sedimentary response to the carbon isotope excursion associated with the PETM.
- Published
- 2021
11. Atmospheric rivers in high-resolution simulations of the Paleocene Eocene Thermal Maximum (PETM)
- Author
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Christine A. Shields, Mark Snyder, William Rush, Jeffrey T. Kiehl, and Mathew Rothstein
- Subjects
010506 paleontology ,Northern Hemisphere ,Paleontology ,Storm ,Forcing (mathematics) ,010502 geochemistry & geophysics ,Oceanography ,Atmospheric sciences ,01 natural sciences ,Streamflow ,Greenhouse gas ,Carbon isotope excursion ,Period (geology) ,Precipitation ,Ecology, Evolution, Behavior and Systematics ,Geology ,0105 earth and related environmental sciences ,Earth-Surface Processes - Abstract
Atmospheric rivers (ARs) and related precipitation are analyzed in high resolution climate simulations during the Eocene using a sophisticated Earth System Model framework. Simulations are conducted across different forcing scenarios spanning the transition from the cooler Late Paleocene period to the Paleocene Eocene Thermal Maximum (PETM), testing both greenhouse gas and orbital sensitivities. AR metrics are compiled and compared across the various simulations and shown to reflect underlying storm tracks where changes in the low-level jet are the primary forcing mechanism for landfall location. Precipitation attributable to ARs is characterized by intensity and amount and compared to total precipitation. Generally, AR precipitation intensity is predominantly moderate, however, this varies by forcing scenario, region, and latitudinal location depending on location of the storm tracks. Extreme rates exist particularly for elevated greenhouse gases and an orbital configuration that maximizes Northern Hemisphere summer insolation. Three regions are diagnosed for landfalling ARs: Western North America, Europe, and Australia. Proxy evidence from the Pyrenees is directly compared to modelled European streamflow and suggests that precipitation produced by ARs can potentially explain the proxy hydrological signal.
- Published
- 2021
12. Atmospheric river landfall‐latitude changes in future climate simulations
- Author
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Jeffrey T. Kiehl and Christine A. Shields
- Subjects
010504 meteorology & atmospheric sciences ,0208 environmental biotechnology ,Global warming ,Climate change ,Global change ,02 engineering and technology ,Subtropics ,Atmospheric river ,01 natural sciences ,020801 environmental engineering ,Latitude ,Geophysics ,Oceanography ,Climatology ,General Earth and Planetary Sciences ,Community Climate System Model ,Environmental science ,Precipitation ,0105 earth and related environmental sciences - Abstract
The latitude of landfall for atmospheric rivers (ARs) is examined in the fully coupled half-degree version of the Community Climate System Model, version 4 (CCSM4) for warm future climate simulations. Two regions are examined: U.S. West Coast/North Pacific ARs, and United Kingdom/North Atlantic ARs. Changes in AR landfall-latitude reflect changes in the atmospheric steering flow. West coast U.S. ARs are projected to push equatorward in response to the subtropical jet climate change. UK AR response is dominated by eddy-driven jets and is seasonally dependent. UK simulated AR response is modest in the winter with the largest relative changes occurring in the seasonal transition months. Precipitation associated with ARs is also projected to increase in intensity under global warming. CCSM4 projects a marked shift to higher rainfall rates for Southern California. Small to modest rainfall rates may increase for all UK latitudes, for the Pacific Northwest, and central and northern California.
- Published
- 2016
13. Simulating the Pineapple Express in the half degree Community Climate System Model, CCSM4
- Author
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Christine A. Shields and Jeffrey T. Kiehl
- Subjects
010504 meteorology & atmospheric sciences ,0208 environmental biotechnology ,Flooding (psychology) ,Tropics ,Climate change ,Storm ,02 engineering and technology ,Atmospheric river ,01 natural sciences ,020801 environmental engineering ,Geophysics ,Climatology ,General Earth and Planetary Sciences ,Community Climate System Model ,Environmental science ,Climate model ,Precipitation ,0105 earth and related environmental sciences - Abstract
Atmospheric rivers are recognized as major contributors to the poleward transport of water vapor. Upon reaching land, these phenomena also play a critical role in extreme precipitation and flooding events. The Pineapple Express (PE) is defined as an atmospheric river extending out of the deep tropics and reaching the west coast of North America. Community Climate System Model (CCSM4) high-resolution ensemble simulations for the twentieth and 21st centuries are diagnosed to identify the PE. Analysis of the twentieth century simulations indicated that the CCSM4 accurately captures the spatial and temporal climatology of the PE. Analysis of the end 21st century simulations indicates a significant increase in storm duration and intensity of precipitation associated with landfall of the PE. Only a modest increase in the number of atmospheric rivers of a few percent is projected for the end of 21st century.
- Published
- 2016
14. Future changes in regional precipitation simulated by a half-degree coupled climate model: Sensitivity to horizontal resolution
- Author
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Jeffrey T. Kiehl, Christine A. Shields, and Gerald A. Meehl
- Subjects
Convection ,Monsoon of South Asia ,Global and Planetary Change ,010504 meteorology & atmospheric sciences ,Climate change ,010502 geochemistry & geophysics ,01 natural sciences ,Degree (temperature) ,Climatology ,General Earth and Planetary Sciences ,Environmental Chemistry ,Environmental science ,Community Climate System Model ,Climate model ,Sensitivity (control systems) ,Precipitation ,0105 earth and related environmental sciences - Abstract
The global fully coupled half-degree Community Climate System Model Version 4 (CCSM4) was integrated for a suite of climate change ensemble simulations including five historical runs, five Representative Concentration Pathway 8.5 [RCP8.5) runs, and a long Pre-Industrial control run. This study focuses on precipitation at regional scales and its sensitivity to horizontal resolution. The half-degree historical CCSM4 simulations are compared to observations, where relevant, and to the standard 1° CCSM4. Both the halfdegree and 1° resolutions are coupled to a nominal 1° ocean. North American and South Asian/Indian monsoon regimes are highlighted because these regimes demonstrate improvements due to higher resolution, primarily because of better-resolved topography. Agriculturally sensitive areas are analyzed and include Southwest, Central, and Southeast U.S., Southern Europe, and Australia. Both mean and extreme precipitation is discussed for convective and large-scale precipitation processes. Convective precipitation tends to decrease with increasing resolution and large-scale precipitation tends to increase. Improvements for the half-degree agricultural regions can be found for mean and extreme precipitation in the Southeast U.S., Southern Europe, and Australian regions. Climate change responses differ between the model resolutions for the U.S. Southwest/Central regions and are seasonally dependent in the Southeast and Australian regions. Both resolutions project a clearmore » drying signal across Southern Europe due to increased greenhouse warming. As a result, differences between resolutions tied to the representation of convective and large-scale precipitation play an important role in the character of the climate change and depend on regional influences.« less
- Published
- 2016
15. A model–model and data–model comparison for the early Eocene hydrological cycle
- Author
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Jeffrey T. Kiehl, M. Heinemann, Christopher D. Roberts, Christine A. Shields, Navjit Sagoo, Arne M.E. Winguth, Paul J. Valdes, Claire Loptson, Matthew J. Carmichael, Matthew Huber, Daniel J. Lunt, Cornelia Winguth, Allegra N. LeGrande, and Richard D. Pancost
- Subjects
lcsh:GE1-350 ,Global and Planetary Change ,geography ,geography.geographical_feature_category ,010504 meteorology & atmospheric sciences ,Stratigraphy ,lcsh:Environmental protection ,Paleontology ,Climate change ,010502 geochemistry & geophysics ,Atmospheric temperature ,01 natural sciences ,Latitude ,lcsh:Environmental pollution ,Climatology ,Latent heat ,Paleoclimatology ,lcsh:TD172-193.5 ,Climate model ,lcsh:TD169-171.8 ,Water cycle ,Ice sheet ,Geology ,lcsh:Environmental sciences ,0105 earth and related environmental sciences - Abstract
A range of proxy observations have recently provided constraints on how Earth's hydrological cycle responded to early Eocene climatic changes. However, comparisons of proxy data to general circulation model (GCM) simulated hydrology are limited and inter-model variability remains poorly characterised. In this work, we undertake an intercomparison of GCM-derived precipitation and P − E distributions within the extended EoMIP ensemble (Eocene Modelling Intercomparison Project; Lunt et al., 2012), which includes previously published early Eocene simulations performed using five GCMs differing in boundary conditions, model structure, and precipitation-relevant parameterisation schemes. We show that an intensified hydrological cycle, manifested in enhanced global precipitation and evaporation rates, is simulated for all Eocene simulations relative to the preindustrial conditions. This is primarily due to elevated atmospheric paleo-CO2, resulting in elevated temperatures, although the effects of differences in paleogeography and ice sheets are also important in some models. For a given CO2 level, globally averaged precipitation rates vary widely between models, largely arising from different simulated surface air temperatures. Models with a similar global sensitivity of precipitation rate to temperature (dP∕dT) display different regional precipitation responses for a given temperature change. Regions that are particularly sensitive to model choice include the South Pacific, tropical Africa, and the Peri-Tethys, which may represent targets for future proxy acquisition. A comparison of early and middle Eocene leaf-fossil-derived precipitation estimates with the GCM output illustrates that GCMs generally underestimate precipitation rates at high latitudes, although a possible seasonal bias of the proxies cannot be excluded. Models which warm these regions, either via elevated CO2 or by varying poorly constrained model parameter values, are most successful in simulating a match with geologic data. Further data from low-latitude regions and better constraints on early Eocene CO2 are now required to discriminate between these model simulations given the large error bars on paleoprecipitation estimates. Given the clear differences between simulated precipitation distributions within the ensemble, our results suggest that paleohydrological data offer an independent means by which to evaluate model skill for warm climates.
- Published
- 2016
16. Le chaos climatique : une question complexe
- Author
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Laurence Lacour and Jeffrey T. Kiehl
- Subjects
General Medicine - Abstract
La demande croissante d’energie a conduit a une destruction environnementale globale, principalement sous la forme de perturbations climatiques. La surconsommation et le chaos climatique sont les symptomes d’un desequilibre psychologique que Jung a nomme dissociation collective. La psychologie analytique offre un point de vue unique sur la relation entre les complexes et la dissociation collective. Cette etude explore comment les complexes et les affects qui y sont associes se manifestent lorsqu’il est question de chaos climatique, et comment l’emergence de defenses specifiques nous empeche d’agir pour resoudre ce probleme. L’article explore ensuite le role crucial joue par les complexes culturels dans le mode de reponse collective face a cette menace environnementale mondiale. Il se conclut par une discussion sur la facon dont nous pouvons travailler avec nos complexes – personnels et collectifs –, afin d’ameliorer l’habitabilite de la Terre pour toutes les especes.
- Published
- 2020
17. Permian Megamonsoon Sensitivity to Paleo-Tethys Warm Pool: Model Simulations using CCSM3
- Author
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Jeffrey T. Kiehl and Christine A. Shields
- Subjects
Pangean megamonsoon ,Monsoon of South Asia ,Sea surface temperature ,Climatology ,Ocean current ,Community Climate System Model ,Precipitation ,Forcing (mathematics) ,Monsoon ,Geology - Abstract
Simulations of the late Permian (251Ma) are analyzed with respect to the northern hemispheric Pangean megamonsoon. We find that the presence and spatial distribution of the warm pool, and not land-sea temperature differences, are the primary forcing agents for the megamonsoon. The land-sea temperature gradient, as a monsoonal mechanism, is tested by eliminating the Cathyasian peninsula and is found to have little impact on the spatial character of the monsoon. Furthermore, the response of the monsoon to the warm pool was tested by removing all Paleo-Tethys equatorial islands, which allows the warm pool to expand and migrate westward thus shifting the pattern of monsoonal precipitation. Additionally, different CO2 regimes are presented, in which a 10-fold change in forcing produces diverging climates and therefore different warm pool and monsoon locales. Atmospheric mass flux for the monsoonal regime is characterized and shown to change with warm pool movement. Tropical and equatorial ocean currents impact the seasonal progression and location of the warm pool. Experiments were conducted using the low-resolution version of Community Climate System Model, Version 3 (CCSM3) in both coupled and fixed sea surface temperature (SST) context. For validation purposes, a modern control is briefly presented with observations and is shown to represent both the spatial and seasonal progression of the Indian monsoon.
- Published
- 2018
18. Greenhouse- and orbital-forced climate extremes during the early Eocene
- Author
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Mathew Rothstein, Jeffrey T. Kiehl, Christine A. Shields, James C Zachos, and Mark Snyder
- Subjects
010504 meteorology & atmospheric sciences ,General Science & Technology ,General Mathematics ,General Physics and Astronomy ,Climate change ,010502 geochemistry & geophysics ,01 natural sciences ,Palaeocene-Eocene Thermal Maximum ,MD Multidisciplinary ,medicine ,Precipitation ,Palaeocene–Eocene Thermal Maximum ,Water cycle ,0105 earth and related environmental sciences ,Global warming ,Flooding (psychology) ,General Engineering ,Northern Hemisphere ,Articles ,Seasonality ,hydrological cycle ,medicine.disease ,climate change ,Climatology ,Greenhouse gas ,Environmental science - Abstract
The Palaeocene–Eocene Thermal Maximum (PETM) was a significant global warming event in Earth's deep past (56 Mya). The warming across the PETM boundary was driven by a rapid rise in greenhouse gases. The event also coincided with a time of maximum insolation in Northern Hemisphere summer. There is increased evidence that the mean warming was accompanied by enhanced seasonality and/or extremes in precipitation (and flooding) and drought. A high horizontal resolution (50 km) global climate model is used to explore changes in the seasonal cycle of surface temperature, precipitation, evaporation minus precipitation and river run-off for regions where proxy data are available. Comparison for the regions indicates the model accurately simulates the observed changes in these climatic characteristics with North American interior warming and drying, and warming and increased river run-off at other regions. The addition of maximum insolation in Northern Hemisphere summer leads to a drier North America, but wetter conditions at most other locations. Long-range transport of atmospheric moisture plays a critical role in explaining regional changes in the water cycle. Such high-frequency variations in precipitation might also help explain discrepancies or misinterpretation of some climate proxies from the same locations, especially where sampling is coarse, i.e. at or greater than the frequency of precession. This article is part of a discussion meeting issue ‘Hyperthermals: rapid and extreme global warming in our geological past’.
- Published
- 2018
19. Human influence on the seasonal cycle of tropospheric temperature
- Author
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Cheng-Zhi Zou, Carl Mears, Susan Solomon, Paul J. Durack, Mark D. Zelinka, Qiang Fu, Stephen Po-Chedley, Ivana Cvijanovic, Jeffrey T. Kiehl, Jeffrey F. Painter, Céline Bonfils, Giuliana Pallotta, Frank J. Wentz, and Benjamin D. Santer
- Subjects
Satellite Imagery ,Multidisciplinary ,010504 meteorology & atmospheric sciences ,Climate Change ,Temperature ,Climate change ,Tropics ,010502 geochemistry & geophysics ,01 natural sciences ,Latitude ,Amplitude ,Climatology ,Environmental science ,Humans ,Climate model ,Satellite imagery ,Satellite ,Human Activities ,Seasons ,Southern Hemisphere ,0105 earth and related environmental sciences - Abstract
'Tis the seasonal Anthropogenic climate change has become clearly observable through many metrics. These include an increase in global annual temperatures, growing heat content of the oceans, and sea level rise owing to the melting of the polar ice sheets and glaciers. Now, Santer et al. report that a human-caused signal in the seasonal cycle of tropospheric temperature can also be measured (see the Perspective by Randel). They use satellite data and the anthropogenic “fingerprint” predicted by climate models to show the extent of the effects and discuss how these changes have been caused. Science , this issue p. eaas8806 ; see also p. 227
- Published
- 2018
20. Latitudinal temperature gradients and high-latitude temperatures during the latest Cretaceous: Congruence of geologic data and climate models
- Author
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Jeffrey T. Kiehl, Christine A. Shields, Christopher R. Scotese, Jacquelyn Scherer, and Garland R. Upchurch
- Subjects
Temperature gradient ,Climatology ,Greenhouse gas ,Paleoclimatology ,Cloud condensation nuclei ,Community Climate System Model ,Geology ,Climate model ,Latitude ,Carbon cycle - Abstract
A major challenge in paleoclimatology is disagreement between data and models for periods of warm climate. Data generally indicate equable conditions and reduced latitudinal temperature gradients, while models generally produce colder conditions and steeper latitudinal gradients except when using very high CO2. Here we show congruence between temperature indicators and climate model output for the cool greenhouse interval of the latest Cretaceous (Maastrichtian) using a global database of terrestrial and marine indicators and fully coupled simulations with the Community Climate System Model version 3. In these simulations we explore potential roles of greenhouse gases and properties of pre-anthropogenic liquid clouds in creating warm conditions. Our model simulations successfully reproduce warm polar temperatures and the latitudinal temperature gradient without overheating the tropics. Best fits for mean annual temperature are simulations that use 6× preindustrial levels of atmospheric CO2, or 2× preindustrial levels of atmospheric CO2 and liquid cloud properties that may reflect pre-anthropogenic levels of cloud condensation nuclei. The Siberian interior is problematic, but this may relate to reconstructed elevation and the presence of lakes. Data and models together indicate tropical sea-surface temperatures ∼5 °C above modern, an equator-to-pole temperature difference of 25–30 °C, and a mid-latitudinal temperature gradient of ∼0.4 °C per 1° latitude, similar to the Eocene. Modified liquid cloud properties allow successful simulation of Maastrichtian climate at the relatively low levels of atmospheric CO2 indicated by proxies and carbon cycle modeling. This supports the suggestion that altered properties of liquid clouds may be an important mechanism of warming during past greenhouse intervals.
- Published
- 2015
21. Acid rain and ozone depletion from pulsed Siberian Traps magmatism
- Author
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Christine A. Shields, Jean-Francois Lamarque, Benjamin A. Black, Linda T. Elkins-Tanton, and Jeffrey T. Kiehl
- Subjects
Extinction event ,Siberian Traps ,Earth science ,Large igneous province ,Atmospheric chemistry ,Magmatism ,Flood basalt ,Geology ,Acid rain ,Ozone depletion - Abstract
The Siberian Traps flood basalts have been invoked as a trigger for the catastrophic end-Permian mass extinction. Widespread aberrant plant remains across the Permian-Triassic boundary provide evidence that atmospheric stress contributed to the collapse in terrestrial diversity. We used detailed estimates of magmatic degassing from the Siberian Traps to complete the first three-dimensional global climate modeling of atmospheric chemistry during eruption of a large igneous province. Our results show that both strongly acidic rain and global ozone collapse are possible transient consequences of episodic pyroclastic volcanism and heating of volatile-rich Siberian country rocks. We suggest that in conjunction with abrupt warming from greenhouse gas emissions, these repeated, rapidly applied atmospheric stresses directly linked Siberian magmatism to end-Permian ecological failure on land. Our comprehensive modeling supplies the first picture of the global distribution and severity of acid rain and ozone depletion, providing testable predictions for the geography of end-Permian environmental proxies.
- Published
- 2014
22. 12. Awakening to One World
- Author
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Jeffrey T. Kiehl
- Published
- 2016
23. Facing Climate Change : An Integrated Path to the Future
- Author
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Jeffrey T. Kiehl and Jeffrey T. Kiehl
- Subjects
- Global environmental change--Psychological aspects, Climatic changes--Psychological aspects, Human ecology--Psychological aspects, Environmental psychology
- Abstract
Facing Climate Change explains why people refuse to accept evidence of a warming planet and shows how to move past partisanship to reach a consensus for action. A climate scientist and licensed Jungian analyst, Jeffrey T. Kiehl examines the psychological phenomena that twist our relationship to the natural world and their role in shaping the cultural beliefs that distance us further from nature. He also accounts for the emotions triggered by the lived experience of climate change and the feelings of fear and loss they inspire, which lead us to deny the reality of our warming planet.But it is not too late. By evaluating our way of being, Kiehl unleashes a potential human emotional understanding that can reform our behavior and help protect the Earth. Kiehl dives deep into the human brain's psychological structures and human spirituality's imaginative power, mining promising resources for creating a healthier connection to the environment—and one another. Facing Climate Change is as concerned with repairing our social and political fractures as it is with reestablishing our ties to the world, teaching us to push past partisanship and unite around the shared attributes that are key to our survival. Kiehl encourages policy makers and activists to appeal to our interdependence as a global society, extracting politics from the process and making decisions about our climate future that are substantial and sustaining.
- Published
- 2016
24. PORT, a CESM tool for the diagnosis of radiative forcing
- Author
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Jeffrey T. Kiehl, William D. Collins, Jean-Francois Lamarque, Francis Vitt, and Andrew Conley
- Subjects
Cloud forcing ,lcsh:Geology ,Forcing (recursion theory) ,Atmospheric radiative transfer codes ,Meteorology ,lcsh:QE1-996.5 ,Radiative transfer ,Environmental science ,Climate model ,Parametrization (atmospheric modeling) ,Atmospheric model ,Radiative forcing ,Atmospheric sciences - Abstract
The Parallel Offline Radiative Transfer (PORT) model is a stand-alone tool, driven by model-generated datasets, that can be used for any radiation calculation that the underlying radiative transfer schemes can perform, such as diagnosing radiative forcing. In its present distribution, PORT isolates the radiation code from the Community Atmosphere Model (CAM4) in the Community Earth System Model (CESM1). The current configuration focuses on CAM4 radiation with the constituents as represented in present-day conditions in CESM1, along with their optical properties. PORT includes an implementation of stratospheric temperature adjustment under the assumption of fixed dynamical heating, which is necessary to compute radiative forcing in addition to the more straightforward instantaneous radiative forcing. PORT can be extended to use radiative constituent distributions from other models or model simulations. Ultimately, PORT can be used with various radiative transfer models. As illustrations of the use of PORT, we perform the computation of radiative forcing from doubling of carbon dioxide, from the change of tropospheric ozone concentration from the year 1850 to 2000, and from present-day aerosols. The radiative forcing from tropospheric ozone (with respect to 1850) generated by a collection of model simulations under the Atmospheric Chemistry and Climate Model Intercomparison Project is found to be 0.34 (with an intermodel standard deviation of 0.07) W m−2. Present-day aerosol direct forcing (relative to no aerosols) is found to be −1.3 W m−2.
- Published
- 2013
25. Balancing the Opposites of Climate Change
- Author
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Jeffrey T. Kiehl
- Subjects
Natural resource economics ,Political science ,Climate change - Published
- 2016
26. Opposites and Our Relationship to Climate Change
- Author
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Jeffrey T. Kiehl
- Subjects
Geography ,Climate change ,Environmental ethics - Published
- 2016
27. Awakening to One World
- Author
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Jeffrey T. Kiehl
- Published
- 2016
28. Why Meaning Is Important to Being in the World
- Author
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Jeffrey T. Kiehl
- Subjects
Sociology ,Meaning (existential) ,Being in the world ,Epistemology - Published
- 2016
29. Learning to Embrace Change
- Author
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Jeffrey T. Kiehl
- Published
- 2016
30. How Images Facilitate Transformation
- Author
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Jeffrey T. Kiehl
- Subjects
business.industry ,Computer science ,Computer vision ,Artificial intelligence ,business ,Transformation (music) - Published
- 2016
31. Exploring Our Being in the World
- Author
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Jeffrey T. Kiehl
- Subjects
Political science ,Media studies ,Being in the world - Published
- 2016
32. Facing Our Fears Associated with Climate Change
- Author
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Jeffrey T. Kiehl
- Subjects
Political science ,Development economics ,Climate change - Published
- 2016
33. Epilogue
- Author
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Jeffrey T. Kiehl
- Published
- 2016
34. Beauty’s Way in the World
- Author
-
Jeffrey T. Kiehl
- Subjects
Aesthetics ,media_common.quotation_subject ,Beauty ,Art ,media_common - Published
- 2016
35. Recognizing the Importance of the Transpersonal
- Author
-
Jeffrey T. Kiehl
- Subjects
Psychoanalysis ,Transpersonal ,Psychology - Published
- 2016
36. How Our Many Worlds Are Entwined
- Author
-
Jeffrey T. Kiehl
- Published
- 2016
37. Facing Climate Change
- Author
-
Jeffrey T. Kiehl
- Subjects
History ,business.industry ,Ecology (disciplines) ,Path (graph theory) ,Environmental resource management ,Climate change ,business - Published
- 2016
38. A Journey from Climate Science to Psychology
- Author
-
Jeffrey T. Kiehl
- Subjects
Critical psychology ,Political science ,Engineering ethics ,Climate science - Published
- 2016
39. SIBERIAN TRAPS SULFUR AND CARBON DEGASSING AND END-PERMIAN CLIMATE FEEDBACKS
- Author
-
Ryan R. Neely, Linda T. Elkins-Tanton, Jean-Francois Lamarque, Christine A. Shields, Benjamin A. Black, Charles G. Bardeen, Jeffrey T. Kiehl, and Michael J. Mills
- Subjects
chemistry ,Permian ,Siberian Traps ,Earth science ,chemistry.chemical_element ,Sulfur ,Carbon ,Geology - Published
- 2016
40. A Jungian Perspective on Global Warming
- Author
-
Jeffrey T. Kiehl
- Subjects
Psyche ,Social Psychology ,Self ,Global warming ,Scientific consensus ,Environmental ethics ,Analytical psychology ,Psychology ,Archetype ,Social psychology ,Individuation ,Applied Psychology ,Shadow (psychology) - Abstract
This article explores the issue of global warming from a Jungian perspective. The scientific consensus is that our warming world is a result of human activity. The effects of continued warming on the planet will be almost unimaginable. Yet, to date, little change in thought or behavior has occurred to address this issue. As such, it is important to explore the deep psychological roots involved with this problem. Jungian psychology provides a unique depth perspective given its views on the structure and dynamics of psyche. Here, the issue of global warming is explored in terms of the Jungian concepts of shadow, complexes, and the archetype of the Self. The process of individuation, whose goal is connecting the ego to the archetype of the Self, is explored as a possible depth psychological approach to addressing global warming. In particular, the concept of holding the tension of opposites between a masculine and feminine view of the global warming issue is emphasized.
- Published
- 2012
41. Climate Sensitivity of the Community Climate System Model, Version 4
- Author
-
Peter R. Gent, Gokhan Danabasoglu, Jeffrey T. Kiehl, Kyle C. Armour, Karen M. Shell, Cecilia M. Bitz, David A. Bailey, and Marika M. Holland
- Subjects
Atmospheric Science ,geography ,geography.geographical_feature_category ,Climate commitment ,Climate change ,Transient climate simulation ,Atmospheric sciences ,Cloud feedback ,Climatology ,Sea ice ,Community Climate System Model ,Climate sensitivity ,Environmental science ,Climate model - Abstract
Equilibrium climate sensitivity of the Community Climate System Model, version 4 (CCSM4) is 3.20°C for 1° horizontal resolution in each component. This is about a half degree Celsius higher than in the previous version (CCSM3). The transient climate sensitivity of CCSM4 at 1° resolution is 1.72°C, which is about 0.2°C higher than in CCSM3. These higher climate sensitivities in CCSM4 cannot be explained by the change to a preindustrial baseline climate. This study uses the radiative kernel technique to show that, from CCSM3 to CCSM4, the global mean lapse-rate feedback declines in magnitude and the shortwave cloud feedback increases. These two warming effects are partially canceled by cooling because of slight decreases in the global mean water vapor feedback and longwave cloud feedback from CCSM3 to CCSM4. A new formulation of the mixed layer, slab-ocean model in CCSM4 attempts to reproduce the SST and sea ice climatology from an integration with a full-depth ocean, and it is integrated with a dynamic sea ice model. These new features allow an isolation of the influence of ocean dynamical changes on the climate response when comparing integrations with the slab ocean and full-depth ocean. The transient climate response of the full-depth ocean version is 0.54 of the equilibrium climate sensitivity when estimated with the new slab-ocean model version for both CCSM3 and CCSM4. The authors argue the ratio is the same in both versions because they have about the same zonal mean pattern of change in ocean surface heat flux, which broadly resembles the zonal mean pattern of net feedback strength.
- Published
- 2012
42. Evaluation of Forecasted Southeast Pacific Stratocumulus in the NCAR, GFDL, and ECMWF Models
- Author
-
James J. Hack, Christopher S. Bretherton, Jeffrey T. Kiehl, Stephen A. Klein, Martin Köhler, Cecile Hannay, Jerry G. Olson, and David L. Williamson
- Subjects
Atmospheric Science ,Boundary layer ,Meteorology ,Diurnal cycle ,Planetary boundary layer ,Climatology ,Environmental science ,Inversion (meteorology) ,Atmospheric model ,EPIC - Abstract
Forecasts of southeast Pacific stratocumulus at 20°S and 85°W during the East Pacific Investigation of Climate (EPIC) cruise of October 2001 are examined with the ECMWF model, the Atmospheric Model (AM) from GFDL, the Community Atmosphere Model (CAM) from NCAR, and the CAM with a revised atmospheric boundary layer formulation from the University of Washington (CAM-UW). The forecasts are initialized from ECMWF analyses and each model is run for 3–5 days to determine the differences with the EPIC field observations. Observations during the EPIC cruise show a well-mixed boundary layer under a sharp inversion. The inversion height and the cloud layer have a strong and regular diurnal cycle. A key problem common to the models is that the planetary boundary layer (PBL) depth is too shallow when compared to EPIC observations. However, it is suggested that improved PBL depths are achieved with more physically realistic PBL schemes: at one end, CAM uses a dry and surface-driven PBL scheme and produces a very shallow PBL, while the ECWMF model uses an eddy-diffusivity/mass-flux approach and produces a deeper and better-mixed PBL. All the models produce a strong diurnal cycle in the liquid water path (LWP), but there are large differences in the amplitude and phase when compared to the EPIC observations. This, in turn, affects the radiative fluxes at the surface and the surface energy budget. This is particularly relevant for coupled simulations as this can lead to a large SST bias.
- Published
- 2009
43. Earth's Global Energy Budget
- Author
-
John T. Fasullo, Jeffrey T. Kiehl, and Kevin E. Trenberth
- Subjects
Earth's energy budget ,Atmosphere ,Atmospheric Science ,Meteorology ,Greenhouse gas ,International Satellite Cloud Climatology Project ,Radiative transfer ,Environmental science ,Radiant energy ,Greenhouse effect ,Energy budget ,Atmospheric sciences - Abstract
An update is provided on the Earth's global annual mean energy budget in the light of new observations and analyses. In 1997, Kiehl and Trenberth provided a review of past estimates and performed a number of radiative computations to better establish the role of clouds and various greenhouse gases in the overall radiative energy flows, with top-of-atmosphere (TOA) values constrained by Earth Radiation Budget Experiment values from 1985 to 1989, when the TOA values were approximately in balance. The Clouds and the Earth's Radiant Energy System (CERES) measurements from March 2000 to May 2004 are used at TOA but adjusted to an estimated imbalance from the enhanced greenhouse effect of 0.9 W m−2. Revised estimates of surface turbulent fluxes are made based on various sources. The partitioning of solar radiation in the atmosphere is based in part on the International Satellite Cloud Climatology Project (ISCCP) FD computations that utilize the global ISCCP cloud data every 3 h, and also accounts for increased ...
- Published
- 2009
44. Quantifying Climate Feedbacks Using Radiative Kernels
- Author
-
Christine A. Shields, Karen M. Shell, Jeffrey T. Kiehl, Robert C. Colman, Brian J. Soden, and Isaac M. Held
- Subjects
Atmospheric Science ,Meteorology ,Climatology ,Cloud cover ,Radiative transfer ,Environmental science ,Climate model ,Climate state ,Forcing (mathematics) ,Albedo ,Atmospheric sciences ,Atmospheric temperature ,Cloud feedback - Abstract
The extent to which the climate will change due to an external forcing depends largely on radiative feedbacks, which act to amplify or damp the surface temperature response. There are a variety of issues that complicate the analysis of radiative feedbacks in global climate models, resulting in some confusion regarding their strengths and distributions. In this paper, the authors present a method for quantifying climate feedbacks based on “radiative kernels” that describe the differential response of the top-of-atmosphere radiative fluxes to incremental changes in the feedback variables. The use of radiative kernels enables one to decompose the feedback into one factor that depends on the radiative transfer algorithm and the unperturbed climate state and a second factor that arises from the climate response of the feedback variables. Such decomposition facilitates an understanding of the spatial characteristics of the feedbacks and the causes of intermodel differences. This technique provides a simple and accurate way to compare feedbacks across different models using a consistent methodology. Cloud feedbacks cannot be evaluated directly from a cloud radiative kernel because of strong nonlinearities, but they can be estimated from the change in cloud forcing and the difference between the full-sky and clear-sky kernels. The authors construct maps to illustrate the regional structure of the feedbacks and compare results obtained using three different model kernels to demonstrate the robustness of the methodology. The results confirm that models typically generate globally averaged cloud feedbacks that are substantially positive or near neutral, unlike the change in cloud forcing itself, which is as often negative as positive.
- Published
- 2008
45. Using the Radiative Kernel Technique to Calculate Climate Feedbacks in NCAR’s Community Atmospheric Model
- Author
-
Christine A. Shields, Jeffrey T. Kiehl, and Karen M. Shell
- Subjects
Atmospheric Science ,Climatology ,Global warming ,Radiative transfer ,Environmental science ,Climate change ,Climate model ,Atmospheric model ,Albedo ,Atmospheric temperature ,Shortwave - Abstract
Climate models differ in their responses to imposed forcings, such as increased greenhouse gas concentrations, due to different climate feedback strengths. Feedbacks in NCAR’s Community Atmospheric Model (CAM) are separated into two components: the change in climate components in response to an imposed forcing and the “radiative kernel,” the effect that climate changes have on the top-of-the-atmosphere (TOA) radiative budget. This technique’s usefulness depends on the linearity of the feedback processes. For the case of CO2 doubling, the sum of the effects of water vapor, temperature, and surface albedo changes on the TOA clear-sky flux is similar to the clear-sky flux changes directly calculated by CAM. When monthly averages are used rather than values from every time step, the global-average TOA shortwave change is underestimated by a quarter, partially as a result of intramonth correlations of surface albedo with the radiative kernel. The TOA longwave flux changes do not depend on the averaging period. The longwave zonal averages are within 10% of the model-calculated values, while the global average differs by only 2%. Cloud radiative forcing (ΔCRF) is often used as a diagnostic of cloud feedback strength. The net effect of the water vapor, temperature, and surface albedo changes on ΔCRF is −1.6 W m−2, based on the kernel technique, while the total ΔCRF from CAM is −1.3 W m−2, indicating these components contribute significantly to ΔCRF and make it more negative. Assuming linearity of the ΔCRF contributions, these results indicate that the net cloud feedback in CAM is positive.
- Published
- 2008
46. Diagnosing Cloud Feedbacks in General Circulation Models
- Author
-
Jeffrey T. Kiehl, Ping Zhu, and James J. Hack
- Subjects
Cloud forcing ,Atmospheric Science ,Radiative flux ,business.industry ,Climatology ,Cloud cover ,Radiative transfer ,Longwave ,Environmental science ,Climate sensitivity ,Cloud computing ,business ,Shortwave - Abstract
In this study, it is shown that the NCAR and GFDL GCMs exhibit a marked difference in climate sensitivity of clouds and radiative fluxes in response to doubled CO2 and ±2-K SST perturbations. The GFDL model predicted a substantial decrease in cloud amount and an increase in cloud condensate in the warmer climate, but produced a much weaker change in net cloud radiative forcing (CRF) than the NCAR model. Using a multiple linear regression (MLR) method, the full-sky radiative flux change at the top of the atmosphere was successfully decomposed into individual components associated with the clear sky and different types of clouds. The authors specifically examined the cloud feedbacks due to the cloud amount and cloud condensate changes involving low, mid-, and high clouds between 60°S and 60°N. It was found that the NCAR and GFDL models predicted the same sign of individual longwave and shortwave feedbacks resulting from the change in cloud amount and cloud condensate for all three types of clouds (low, mid, and high) despite the different cloud and radiation schemes used in the models. However, since the individual longwave and shortwave feedbacks resulting from the change in cloud amount and cloud condensate generally have the opposite signs, the net cloud feedback is a subtle residual of all. Strong cancellations between individual cloud feedbacks may result in a weak net cloud feedback. This result is consistent with the findings of the previous studies, which used different approaches to diagnose cloud feedbacks. This study indicates that the proposed MLR approach provides an easy way to efficiently expose the similarity and discrepancy of individual cloud feedback processes between GCMs, which are hidden in the total cloud feedback measured by CRF. Most importantly, this method has the potential to be applied to satellite measurements. Thus, it may serve as a reliable and efficient method to investigate cloud feedback mechanisms on short-term scales by comparing simulations with available observations, which may provide a useful way to identify the cause for the wide spread of cloud feedbacks in GCMs.
- Published
- 2007
47. Environmental effects of large igneous province magmatism: a Siberian perspective
- Author
-
Christine A. Shields, Jean-Francois Lamarque, Benjamin A. Black, Linda T. Elkins-Tanton, and Jeffrey T. Kiehl
- Subjects
Earth science ,Large igneous province ,Perspective (graphical) ,Magmatism ,Petrology ,Geology - Published
- 2015
48. Radiative and Dynamical Feedbacks over the Equatorial Cold Tongue: Results from Nine Atmospheric GCMs
- Author
-
William D. Collins, Gerald A. Meehl, S. A. Klein, Jeffrey T. Kiehl, James J. Hack, Tao Zhang, Curt Covey, Isaac M. Held, De-Zheng Sun, and Max J. Suarez
- Subjects
Atmospheric Science ,Sea surface temperature ,La Niña ,Cold tongue ,General Circulation Model ,Climatology ,Radiative transfer ,Environmental science ,Energy flux ,Climate model ,Atmospheric model ,Atmospheric sciences - Abstract
The equatorial Pacific is a region with strong negative feedbacks. Yet coupled general circulation models (GCMs) have exhibited a propensity to develop a significant SST bias in that region, suggesting an unrealistic sensitivity in the coupled models to small energy flux errors that inevitably occur in the individual model components. Could this “hypersensitivity” exhibited in a coupled model be due to an underestimate of the strength of the negative feedbacks in this region? With this suspicion, the feedbacks in the equatorial Pacific in nine atmospheric GCMs (AGCMs) have been quantified using the interannual variations in that region and compared with the corresponding calculations from the observations. The nine AGCMs are the NCAR Community Climate Model version 1 (CAM1), the NCAR Community Climate Model version 2 (CAM2), the NCAR Community Climate Model version 3 (CAM3), the NCAR CAM3 at T85 resolution, the NASA Seasonal-to-Interannual Prediction Project (NSIPP) Atmospheric Model, the Hadley Centre Atmospheric Model (HadAM3), the Institut Pierre Simon Laplace (IPSL) model (LMDZ4), the Geophysical Fluid Dynamics Laboratory (GFDL) AM2p10, and the GFDL AM2p12. All the corresponding coupled runs of these nine AGCMs have an excessive cold tongue in the equatorial Pacific. The net atmospheric feedback over the equatorial Pacific in the two GFDL models is found to be comparable to the observed value. All other models are found to have a weaker negative net feedback from the atmosphere—a weaker regulating effect on the underlying SST than the real atmosphere. Except for the French (IPSL) model, a weaker negative feedback from the cloud albedo and a weaker negative feedback from the atmospheric transport are the two leading contributors to the weaker regulating effect from the atmosphere. The underestimate of the strength of the negative feedbacks by the models is apparently linked to an underestimate of the equatorial precipitation response. All models have a stronger water vapor feedback than that indicated in Earth Radiation Budget Experiment (ERBE) observations. These results confirm the suspicion that an underestimate of the regulatory effect from the atmosphere over the equatorial Pacific region is a prevalent problem. The results also suggest, however, that a weaker regulatory effect from the atmosphere is unlikely solely responsible for the hypersensitivity in all models. The need to validate the feedbacks from the ocean transport is therefore highlighted.
- Published
- 2006
49. The Climate Sensitivity of the Community Climate System Model Version 3 (CCSM3)
- Author
-
Christine A. Shields, Jeffrey T. Kiehl, James J. Hack, and William D. Collins
- Subjects
Atmospheric Science ,Climate commitment ,Atmospheric model ,Transient climate simulation ,Atmospheric sciences ,chemistry.chemical_compound ,chemistry ,Climatology ,Carbon dioxide ,Community Climate System Model ,Environmental science ,Climate sensitivity ,Transient (oscillation) ,Sensitivity (control systems) - Abstract
The climate sensitivity of the Community Climate System Model (CCSM) is described in terms of the equilibrium change in surface temperature due to a doubling of carbon dioxide in a slab ocean version of the Community Atmosphere Model (CAM) and the transient climate response, which is the surface temperature change at the point of doubling of carbon dioxide in a 1% yr−1 CO2 simulation with the fully coupled CCSM. For a fixed atmospheric horizontal resolution across model versions, we show that the equilibrium sensitivity has monotonically increased across CSM1.4, CCSM2, to CCSM3 from 2.01° to 2.27° to 2.47°C, respectively. The transient climate response for these versions is 1.44° to 1.09° to 1.48°C, respectively. Using climate feedback analysis, it is shown that both clear-sky and cloudy-sky processes have contributed to the changes in transient climate response. The dependence of these sensitivities on horizontal resolution is also explored. The equilibrium sensitivity of the high-resolution (T85) version of CCSM3 is 2.71°C, while the equilibrium response for the low-resolution model (T31) is 2.32°C. It is shown that the shortwave cloud response of the high-resolution version of the CCSM3 is anomalous compared to the low- and moderate-resolution versions.
- Published
- 2006
50. A comparison of low-latitude cloud properties and their response to climate change in three AGCMs sorted into regimes using mid-tropospheric vertical velocity
- Author
-
Isaac M. Held, Christopher S. Bretherton, Jeffrey T. Kiehl, Julio T. Bacmeister, Ming Zhao, Stephen A. Klein, Brian J. Soden, and Matthew C. Wyant
- Subjects
Troposphere ,Cloud forcing ,Atmospheric Science ,Mixed layer ,Climatology ,Cloud cover ,Cloud fraction ,Climate change ,Environmental science ,Cirrus ,Atmospheric model ,Atmospheric sciences - Abstract
Low-latitude cloud distributions and cloud responses to climate perturbations are compared in near-current versions of three leading U.S. AGCMs, the NCAR CAM 3.0, the GFDL AM2.12b, and the NASA GMAO NSIPP-2 model. The analysis technique of Bony et al. (Clim Dyn 22:71–86, 2004) is used to sort cloud variables by dynamical regime using the monthly mean pressure velocity ω at 500 hPa from 30S to 30N. All models simulate the climatological monthly mean top-of-atmosphere longwave and shortwave cloud radiative forcing (CRF) adequately in all ω-regimes. However, they disagree with each other and with ISCCP satellite observations in regime-sorted cloud fraction, condensate amount, and cloud-top height. All models have too little cloud with tops in the middle troposphere and too much thin cirrus in ascent regimes. In subsidence regimes one model simulates cloud condensate to be too near the surface, while another generates condensate over an excessively deep layer of the lower troposphere. Standardized climate perturbation experiments of the three models are also compared, including uniform SST increase, patterned SST increase, and doubled CO2 over a mixed layer ocean. The regime-sorted cloud and CRF perturbations are very different between models, and show lesser, but still significant, differences between the same model simulating different types of imposed climate perturbation. There is a negative correlation across all general circulation models (GCMs) and climate perturbations between changes in tropical low cloud cover and changes in net CRF, suggesting a dominant role for boundary layer cloud in these changes. For some of the cases presented, upper-level clouds in deep convection regimes are also important, and changes in such regimes can either reinforce or partially cancel the net CRF response from the boundary layer cloud in subsidence regimes. This study highlights the continuing uncertainty in both low and high cloud feedbacks simulated by GCMs.
- Published
- 2006
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