44 results on '"Harry J. Dowsett"'
Search Results
2. The PRISM4 (mid-Piacenzian) paleoenvironmental reconstruction
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David B. Rowley, Kevin M. Foley, Harry J. Dowsett, Alan M. Haywood, Ulrich Salzmann, Aisling M. Dolan, Alessandro M. Forte, Marci M. Robinson, Jerry X. Mitrovica, Matthew J. Pound, Robert Moucha, and Mark A. Chandler
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Piacenzian ,010504 meteorology & atmospheric sciences ,Stratigraphy ,lcsh:Environmental protection ,F800 ,F600 ,Present day ,010502 geochemistry & geophysics ,01 natural sciences ,lcsh:Environmental pollution ,Sea ice ,lcsh:TD169-171.8 ,Glacial period ,Sea level ,lcsh:Environmental sciences ,0105 earth and related environmental sciences ,lcsh:GE1-350 ,Global and Planetary Change ,geography ,geography.geographical_feature_category ,Paleontology ,Vegetation ,Ocean surface topography ,13. Climate action ,Climatology ,lcsh:TD172-193.5 ,Climate model ,Geology - Abstract
The mid-Piacenzian is known as a period of relative warmth when compared to the present day. A comprehensive understanding of conditions during the Piacenzian serves as both a conceptual model and a source for boundary conditions as well as means of verification of global climate model experiments. In this paper we present the PRISM4 reconstruction, a paleoenvironmental reconstruction of the mid-Piacenzian ( ∼ 3 Ma) containing data for paleogeography, land and sea ice, sea-surface temperature, vegetation, soils, and lakes. Our retrodicted paleogeography takes into account glacial isostatic adjustments and changes in dynamic topography. Soils and lakes, both significant as land surface features, are introduced to the PRISM reconstruction for the first time. Sea-surface temperature and vegetation reconstructions are unchanged but now have confidence assessments. The PRISM4 reconstruction is being used as boundary condition data for the Pliocene Model Intercomparison Project Phase 2 (PlioMIP2) experiments.
- Published
- 2016
3. RECONSTRUCTING INDIAN MONSOON STRENGTH IN THE BAY OF BENGAL DURING THE PLIOCENE M2 EVENT: ESTIMATION OF PALEOSALINITY LEVELS
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Marci M. Robinson, Kristen E. St. John, Kristen L. Steele, and Harry J. Dowsett
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Monsoon of South Asia ,Estimation ,Oceanography ,Climatology ,Event (relativity) ,BENGAL ,Paleosalinity ,Bay ,Geology - Published
- 2017
4. Simulations of the mid-Pliocene Warm Period using two versions of the NASA/GISS ModelE2-R Coupled Model
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Linda E. Sohl, J. Jonas, Maxwell Kelley, Harry J. Dowsett, and Mark A. Chandler
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010506 paleontology ,geography ,geography.geographical_feature_category ,010504 meteorology & atmospheric sciences ,Global warming ,lcsh:QE1-996.5 ,Climate change ,Atmospheric model ,01 natural sciences ,lcsh:Geology ,Sea surface temperature ,13. Climate action ,Effects of global warming ,Climatology ,Sea ice ,Pliocene climate ,Environmental science ,Climate model ,0105 earth and related environmental sciences - Abstract
The mid-Pliocene Warm Period (mPWP) bears many similarities to aspects of future global warming as projected by the Intergovernmental Panel on Climate Change (IPCC, 2007). Both marine and terrestrial data point to high-latitude temperature amplification, including large decreases in sea ice and land ice, as well as expansion of warmer climate biomes into higher latitudes. Here we present our most recent simulations of the mid-Pliocene climate using the CMIP5 version of the NASA/GISS Earth System Model (ModelE2-R). We describe the substantial impact associated with a recent correction made in the implementation of the Gent-McWilliams ocean mixing scheme (GM), which has a large effect on the simulation of ocean surface temperatures, particularly in the North Atlantic Ocean. The effect of this correction on the Pliocene climate results would not have been easily determined from examining its impact on the preindustrial runs alone, a useful demonstration of how the consequences of code improvements as seen in modern climate control runs do not necessarily portend the impacts in extreme climates. Both the GM-corrected and GM-uncorrected simulations were contributed to the Pliocene Model Intercomparison Project (PlioMIP) Experiment 2. Many findings presented here corroborate results from other PlioMIP multi-model ensemble papers, but we also emphasise features in the ModelE2-R simulations that are unlike the ensemble means. The corrected version yields results that more closely resemble the ocean core data as well as the PRISM3D reconstructions of the mid-Pliocene, especially the dramatic warming in the North Atlantic and Greenland-Iceland-Norwegian Sea, which in the new simulation appears to be far more realistic than previously found with older versions of the GISS model. Our belief is that continued development of key physical routines in the atmospheric model, along with higher resolution and recent corrections to mixing parameterisations in the ocean model, have led to an Earth System Model that will produce more accurate projections of future climate.
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- 2013
5. Sensitivity of Pliocene Arctic climate to orbital forcing, atmospheric CO2 and sea ice albedo parameterisation
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Alan M. Haywood, Harry J. Dowsett, Steven J. Pickering, and Fergus W. Howell
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Arctic sea ice decline ,geography ,geography.geographical_feature_category ,010504 meteorology & atmospheric sciences ,Ice-albedo feedback ,010502 geochemistry & geophysics ,Atmospheric sciences ,01 natural sciences ,Arctic ice pack ,Arctic geoengineering ,Geophysics ,13. Climate action ,Space and Planetary Science ,Geochemistry and Petrology ,Climatology ,Sea ice thickness ,Earth and Planetary Sciences (miscellaneous) ,Sea ice ,Cryosphere ,Sea ice concentration ,Geology ,0105 earth and related environmental sciences - Abstract
General circulation model (GCM) simulations of the mid-Pliocene Warm Period (mPWP, 3.264 to 3.025 Myr ago) do not reproduce the magnitude of Northern Hemisphere high latitude surface air and sea surface temperature (SAT and SST) warming that proxy data indicate. There is also large uncertainty regarding the state of sea ice cover in the mPWP. Evidence for both perennial and seasonal mPWP Arctic sea ice is found through analyses of marine sediments, whilst in a multi-model ensemble of mPWP climate simulations, half of the ensemble simulated ice-free summer Arctic conditions. Given the strong influence that sea ice exerts on high latitude temperatures, an understanding of the nature of mPWP Arctic sea ice would be highly beneficial. Using the HadCM3 GCM, this paper explores the impact of various combinations of potential mPWP orbital forcing, atmospheric CO 2 concentrations and minimum sea ice albedo on sea ice extent and high latitude warming. The focus is on the Northern Hemisphere, due to availability of proxy data, and the large data–model discrepancies in this region. Changes in orbital forcings are demonstrated to be sufficient to alter the Arctic sea ice simulated by HadCM3 from perennial to seasonal. However, this occurs only when atmospheric CO 2 concentrations exceed 300 ppm. Reduction of the minimum sea ice albedo from 0.5 to 0.2 is also sufficient to simulate seasonal sea ice, with any of the combinations of atmospheric CO 2 and orbital forcing. Compared to a mPWP control simulation, monthly mean increases north of 60°N of up to 4.2 °C (SST) and 9.8 °C (SAT) are simulated. With varying CO 2 , orbit and sea ice albedo values we are able to reproduce proxy temperature records that lean towards modest levels of high latitude warming, but other proxy data showing greater warming remain beyond the reach of our model. This highlights the importance of additional proxy records at high latitudes and ongoing efforts to compare proxy signals between sites.
- Published
- 2016
6. The Pliocene Model Intercomparison Project (PlioMIP) Phase 2:scientific objectives and experimental design
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Alan M. Haywood, Aisling M. Dolan, David B. Rowley, Mark A. Chandler, Ayako Abe-Ouchi, Daniel J. Lunt, Harry J. Dowsett, Ulrich Salzmann, Matthew J. Pound, Bette L. Otto-Bliesner, and Stephen J. Hunter
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010506 paleontology ,010504 meteorology & atmospheric sciences ,Meteorology ,Stratigraphy ,lcsh:Environmental protection ,Climate change ,Atmospheric Model Intercomparison Project ,Context (language use) ,F600 ,01 natural sciences ,lcsh:Environmental pollution ,Paleoclimatology ,Pliocene climate ,Bathymetry ,lcsh:TD169-171.8 ,lcsh:Environmental sciences ,0105 earth and related environmental sciences ,lcsh:GE1-350 ,Global and Planetary Change ,geography ,geography.geographical_feature_category ,Paleontology ,13. Climate action ,Climatology ,lcsh:TD172-193.5 ,Environmental science ,Climate model ,Ice sheet - Abstract
The Pliocene Model Intercomparison Project (PlioMIP) is a co-ordinated international climate modelling initiative to study and understand climate and environments of the Late Pliocene, as well as their potential relevance in the context of future climate change. PlioMIP examines the consistency of model predictions in simulating Pliocene climate and their ability to reproduce climate signals preserved by geological climate archives. Here we provide a description of the aim and objectives of the next phase of the model intercomparison project (PlioMIP Phase 2), and we present the experimental design and boundary conditions that will be utilized for climate model experiments in Phase 2. Following on from PlioMIP Phase 1, Phase 2 will continue to be a mechanism for sampling structural uncertainty within climate models. However, Phase 1 demonstrated the requirement to better understand boundary condition uncertainties as well as uncertainty in the methodologies used for data–model comparison. Therefore, our strategy for Phase 2 is to utilize state-of-the-art boundary conditions that have emerged over the last 5 years. These include a new palaeogeographic reconstruction, detailing ocean bathymetry and land–ice surface topography. The ice surface topography is built upon the lessons learned from offline ice sheet modelling studies. Land surface cover has been enhanced by recent additions of Pliocene soils and lakes. Atmospheric reconstructions of palaeo-CO2 are emerging on orbital timescales, and these are also incorporated into PlioMIP Phase 2. New records of surface and sea surface temperature change are being produced that will be more temporally consistent with the boundary conditions and forcings used within models. Finally we have designed a suite of prioritized experiments that tackle issues surrounding the basic understanding of the Pliocene and its relevance in the context of future climate change in a discrete way.
- Published
- 2016
7. On the causes of mid-Pliocene warmth and polar amplification
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Ulrich Salzmann, Alan M. Haywood, Daniel J. Lunt, Claire Loptson, Paul J. Valdes, Harry J. Dowsett, and Gavin A. Schmidt
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geography ,geography.geographical_feature_category ,010504 meteorology & atmospheric sciences ,Global warming ,Northern Hemisphere ,Climate change ,Orography ,010502 geochemistry & geophysics ,Atmospheric sciences ,01 natural sciences ,Geophysics ,13. Climate action ,Space and Planetary Science ,Geochemistry and Petrology ,Climatology ,Earth and Planetary Sciences (miscellaneous) ,Polar amplification ,sense organs ,Ice sheet ,skin and connective tissue diseases ,Southern Hemisphere ,Geology ,0105 earth and related environmental sciences ,Orographic lift - Abstract
The mid-Pliocene (approximately 3 to 3.3 Ma ago), is a period of sustained global warmth in comparison to the late Quaternary (0 to approximately 1 Ma ago), and has potential to inform predictions of long-term future climate change. However, given that several processes potentially contributed, relatively little is understood about the reasons for the observed warmth, or the associated polar amplification. Here, using a modelling approach and a novel factorisation method, we assess the relative contributions to mid-Pliocene warmth from: elevated CO2, lowered orography, and vegetation and ice sheet changes. The results show that on a global scale, the largest contributor to mid-Pliocene warmth is elevated CO2. However, in terms of polar amplification, changes to ice sheets contribute significantly in the Southern Hemisphere, and orographic changes contribute significantly in the Northern Hemisphere. We also carry out an energy balance analysis which indicates that that on a global scale, surface albedo and atmospheric emmissivity changes dominate over cloud changes. We investigate the sensitivity of our results to uncertainties in the prescribed CO2 and orographic changes, to derive uncertainty ranges for the various contributing processes.
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- 2012
8. Aerosols shift lake ecosystem
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Harry J. Dowsett
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0301 basic medicine ,010504 meteorology & atmospheric sciences ,Limnology ,Lake ecosystem ,Loess plateau ,respiratory system ,Environmental Science (miscellaneous) ,complex mixtures ,01 natural sciences ,03 medical and health sciences ,030104 developmental biology ,Hydrology (agriculture) ,Climatology ,Environmental science ,Physical geography ,Monsoon precipitation ,Social Sciences (miscellaneous) ,0105 earth and related environmental sciences - Abstract
Anthropogenic aerosols over the Chinese Loess Plateau have diminished monsoon precipitation and concomitant soil erosion that plagues the region. Now, a reconstruction documents the differences between historical warming events and the present, highlighting the paradoxical implications of decreasing atmospheric aerosols.
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- 2017
9. Sensitivity of Pliocene ice sheets to orbital forcing
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Alan M. Haywood, Steven J. Pickering, Aisling M. Dolan, Daniel J. Lunt, Harry J. Dowsett, Daniel J. Hill, and Stephen J. Hunter
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geography ,geography.geographical_feature_category ,010504 meteorology & atmospheric sciences ,Ice stream ,Paleontology ,Antarctic sea ice ,010502 geochemistry & geophysics ,Oceanography ,01 natural sciences ,Arctic ice pack ,Ice-sheet model ,13. Climate action ,Climatology ,Sea ice thickness ,Sea ice ,Cryosphere ,Ice sheet ,Ecology, Evolution, Behavior and Systematics ,Geology ,0105 earth and related environmental sciences ,Earth-Surface Processes - Abstract
The stability of the Earth's major ice sheets is a critical uncertainty in predictions of future climate and sea level change. One method of investigating the behaviour of the Greenland and the Antarctic ice sheets in a warmer-than-modern climate is to look back at past warm periods of Earth history, for example the Pliocene. This paper presents climate and ice sheet modelling results for the mid-Pliocene warm period (mPWP; 3.3 to 3.0 million years ago), which has been identified as a key interval for understanding warmer-than-modern climates (Jansen et al., 2007). Using boundary conditions supplied by the United States Geological Survey PRISM Group (Pliocene Research, Interpretation and Synoptic Mapping), the Hadley Centre coupled ocean–atmosphere climate model (HadCM3) and the British Antarctic Survey Ice Sheet Model (BASISM), we show large reductions in the Greenland and East Antarctic Ice Sheets (GrIS and EAIS) compared to modern in standard mPWP experiments. We also present the first results illustrating the variability of the ice sheets due to realistic orbital forcing during the mid-Pliocene. While GrIS volumes are lower than modern under even the most extreme (cold) mid-Pliocene orbit (losing at least 35% of its ice mass), the EAIS can both grow and shrink, losing up to 20% or gaining up to 10% of its present-day volume. The changes in ice sheet volume incurred by altering orbital forcing alone means that global sea level can vary by more than 25 m during the mid-Pliocene. However, we have also shown that the response of the ice sheets to mPWP orbital hemispheric forcing can be in anti-phase, whereby the greatest reductions in EAIS volume are concurrent with the smallest reductions of the GrIS. If this anti-phase relationship is in operation throughout the mPWP, then the total eustatic sea level response would be dampened compared to the ice sheet fluctuations that are theoretically possible. This suggests that maximum eustatic sea level rise does not correspond to orbital maxima, but occurs at times where the anti-phasing of Northern and Southern Hemisphere ice sheet retreat is minimised.
- Published
- 2011
10. Bathymetric controls on Pliocene North Atlantic and Arctic sea surface temperature and deepwater production
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S. M. Jones, Marci M. Robinson, Alan M. Haywood, Paul J. Valdes, Daniel J. Hill, and Harry J. Dowsett
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geography ,geography.geographical_feature_category ,Arctic dipole anomaly ,Paleontology ,Subsidence (atmosphere) ,Mid-ocean ridge ,Oceanography ,Latitude ,Sea surface temperature ,Arctic ,Climatology ,Atlantic multidecadal oscillation ,Bathymetry ,Ecology, Evolution, Behavior and Systematics ,Geology ,Earth-Surface Processes - Abstract
The mid-Pliocene warm period (MPWP; ~ 3.3 to 3.0 Ma) is the most recent interval in Earth's history in which global temperatures reached and remained at levels similar to those projected for the near future. The distribution of global warmth, however, was different than today in that the high latitudes warmed more than the tropics. Multiple temperature proxies indicate significant sea surface warming in the North Atlantic and Arctic Oceans during the MPWP, but predictions from a fully coupled ocean–atmosphere model (HadCM3) have so far been unable to fully predict the large scale of sea surface warming in the high latitudes. If climate proxies accurately represent Pliocene conditions, and if no weakness exists in the physics of the model, then model boundary conditions may be in error. Here we alter a single boundary condition (bathymetry) to examine if Pliocene high latitude warming was aided by an increase in poleward heat transport due to changes in the subsidence of North Atlantic Ocean ridges. We find an increase in both Arctic sea surface temperature and deepwater production in model experiments that incorporate a deepened Greenland–Scotland Ridge. These results offer both a mechanism for the warming in the North Atlantic and Arctic Oceans indicated by numerous proxies and an explanation for the apparent disparity between proxy data and model simulations of Pliocene northern North Atlantic and Arctic Ocean conditions. Determining the causes of Pliocene warmth remains critical to fully understanding comparisons of the Pliocene warm period to possible future climate change scenarios.
- Published
- 2011
11. Sea surface temperatures of the mid-Piacenzian Warm Period: A comparison of PRISM3 and HadCM3
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Danielle K. Stoll, Daniel J. Hill, Marci M. Robinson, Alan M. Haywood, Kevin M. Foley, Paul J. Valdes, Harry J. Dowsett, and Daniel J. Lunt
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Piacenzian ,Paleontology ,Oceanography ,HadCM3 ,Latitude ,Marine Sciences ,Sea surface temperature ,Meteorology and Climatology ,Climatology ,Earth Sciences ,Upwelling ,Climate model ,Bathymetry ,Thermocline ,Ecology, Evolution, Behavior and Systematics ,Geology ,Earth-Surface Processes - Abstract
It is essential to document how well the current generation of climate models performs in simulating past climates to have confidence in their ability to project future conditions. We present the first global, in-depth comparison of Pliocene sea surface temperature (SST) estimates from a coupled ocean–atmosphere climate model experiment and a SST reconstruction based on proxy data. This enables the identification of areas in which both the climate model and the proxy dataset require improvement. In general, the fit between model-produced SST anomalies and those formed from the available data is very good. We focus our discussion on three regions where the data–model anomaly exceeds 2 °C. 1) In the high latitude North Pacific, a systematic model error may result in anomalies that are too cold. Also, the deeper Pliocene thermocline may cause disagreement along the California margin; either the upwelling in the model is too strong or the modeled thermocline is not deep enough. 2) In the North Atlantic, the model predicts cooling in the center of a data-based warming trend that steadily increases with latitude from + 1.5 °C to >+ 6 °C. The discrepancy may arise because the modeled North Atlantic Current is too zonal compared to reality, which is reinforced by the lowering of the altitude of the Pliocene Western Cordillera Mountains. In addition, the model's use of modern bathymetry in the higher latitudes may have led the model to underestimate the northward penetration of warmer surface water into the Arctic. 3) Finally, though the data and model show good general agreement across most of the Southern Ocean, a few locations show offsets due to the modern land–sea mask used in the model. Additional considerations could account for many of the modest data–model anomalies, such as differences between calibration climatologies, the oversimplification of the seasonal cycle, and differences between SST proxies (i.e. seasonality and water depth). New SST estimates from data-sparse and regionally important areas will greatly enhance our ability to judge model performance.
- Published
- 2011
12. Pliocene Model Intercomparison Project (PlioMIP): experimental design and boundary conditions (Experiment 2)
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Alan M. Haywood, Aisling M. Dolan, Marci M. Robinson, Harry J. Dowsett, Danielle K. Stoll, Mark A. Chandler, Bette L. Otto-Bliesner, and Daniel J. Lunt
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Coupled model intercomparison project ,010506 paleontology ,010504 meteorology & atmospheric sciences ,lcsh:QE1-996.5 ,Climate change ,Atmospheric Model Intercomparison Project ,010502 geochemistry & geophysics ,Atmospheric sciences ,01 natural sciences ,lcsh:Geology ,13. Climate action ,Climatology ,Initial phase ,Pliocene climate ,Environmental science ,Model development ,Climate model ,Boundary value problem ,0105 earth and related environmental sciences - Abstract
The Palaeoclimate Modelling Intercomparison Project has expanded to include a model intercomparison for the mid-Pliocene warm period (3.29 to 2.97 million yr ago). This project is referred to as PlioMIP (the Pliocene Model Intercomparison Project). Two experiments have been agreed upon and together compose the initial phase of PlioMIP. The first (Experiment 1) is being performed with atmosphere-only climate models. The second (Experiment 2) utilises fully coupled ocean-atmosphere climate models. Following on from the publication of the experimental design and boundary conditions for Experiment 1 in Geoscientific Model Development, this paper provides the necessary description of differences and/or additions to the experimental design for Experiment 2.
- Published
- 2011
13. Are there pre-Quaternary geological analogues for a future greenhouse warming?
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Matthew J. Pound, Mark Williams, Alan M. Haywood, Daniel J. Lunt, Daniel J. Hill, Andy Ridgwell, Harry J. Dowsett, Jane E. Francis, and Aisling M. Dolan
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Meteorology ,General Mathematics ,General Engineering ,Climate commitment ,General Physics and Astronomy ,Climate change ,Earth system science ,Climatology ,Greenhouse gas ,Paleoclimatology ,Climate sensitivity ,Environmental science ,Climate model ,Climate state - Abstract
Given the inherent uncertainties in predicting how climate and environments will respond to anthropogenic emissions of greenhouse gases, it would be beneficial to society if science could identify geological analogues to the human race’s current grand climate experiment . This has been a focus of the geological and palaeoclimate communities over the last 30 years, with many scientific papers claiming that intervals in Earth history can be used as an analogue for future climate change. Using a coupled ocean–atmosphere modelling approach, we test this assertion for the most probable pre-Quaternary candidates of the last 100 million years: the Mid- and Late Cretaceous, the Palaeocene–Eocene Thermal Maximum (PETM), the Early Eocene, as well as warm intervals within the Miocene and Pliocene epochs. These intervals fail as true direct analogues since they either represent equilibrium climate states to a long-term CO 2 forcing—whereas anthropogenic emissions of greenhouse gases provide a progressive (transient) forcing on climate—or the sensitivity of the climate system itself to CO 2 was different. While no close geological analogue exists, past warm intervals in Earth history provide a unique opportunity to investigate processes that operated during warm (high CO 2 ) climate states. Palaeoclimate and environmental reconstruction/modelling are facilitating the assessment and calculation of the response of global temperatures to increasing CO 2 concentrations in the longer term (multiple centuries); this is now referred to as the Earth System Sensitivity, which is critical in identifying CO 2 thresholds in the atmosphere that must not be crossed to avoid dangerous levels of climate change in the long term. Palaeoclimatology also provides a unique and independent way to evaluate the qualities of climate and Earth system models used to predict future climate.
- Published
- 2011
14. Pliocene Model Intercomparison Project (PlioMIP): experimental design and boundary conditions (Experiment 1)
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Alan M. Haywood, Aisling M. Dolan, Marci M. Robinson, Daniel J. Hill, Ulrich Salzmann, Mark A. Chandler, Harry J. Dowsett, Linda E. Sohl, Nan Rosenbloom, Bette L. Otto-Bliesner, and Daniel J. Lunt
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010506 paleontology ,010504 meteorology & atmospheric sciences ,Glaciology ,lcsh:QE1-996.5 ,F600 ,010502 geochemistry & geophysics ,01 natural sciences ,Marine Sciences ,lcsh:Geology ,Fully coupled ,Meteorology and Climatology ,13. Climate action ,Climatology ,Pliocene climate ,Earth Sciences ,Environmental science ,Climate model ,0105 earth and related environmental sciences - Abstract
In 2008 the temporal focus of the Palaeoclimate Modelling Intercomparison Project was expanded to include a model intercomparison for the mid-Pliocene warm period (3.29–2.97 million years ago). This project is referred to as PlioMIP (Pliocene Model Intercomparison Project). Two experiments have been agreed upon and comprise phase 1 of PlioMIP. The first (Experiment 1) will be performed with atmosphere-only climate models. The second (Experiment 2) will utilise fully coupled ocean-atmosphere climate models. The aim of this paper is to provide a detailed model intercomparison project description which documents the experimental design in a more detailed way than has previously been done in the literature. Specifically, this paper describes the experimental design and boundary conditions that will be utilised for Experiment 1 of PlioMIP.
- Published
- 2010
15. Earth system sensitivity inferred from Pliocene modelling and data
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Daniel J. Lunt, Gavin A. Schmidt, Ulrich Salzmann, Paul J. Valdes, Harry J. Dowsett, and Alan M. Haywood
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Carbon dioxide in Earth's atmosphere ,010504 meteorology & atmospheric sciences ,Climate oscillation ,Global warming ,Climate commitment ,010502 geochemistry & geophysics ,Atmospheric sciences ,01 natural sciences ,13. Climate action ,Climatology ,Greenhouse gas ,General Earth and Planetary Sciences ,Climate sensitivity ,Environmental science ,Climate model ,Climate state ,0105 earth and related environmental sciences - Abstract
Quantifying the equilibrium response of global temperatures to an increase in atmospheric carbon dioxide concentrations is one of the cornerstones of climate research. Components of the Earth’s climate system that vary over long timescales, such as ice sheets and vegetation, could have an important effect on this temperature sensitivity, but have often been neglected. Here we use a coupled atmosphere–ocean general circulation model to simulate the climate of the mid-Pliocene warm period (about three million years ago), and analyse the forcings and feedbacks that contributed to the relatively warm temperatures. Furthermore, we compare our simulation with proxy records of mid-Pliocene sea surface temperature. Taking these lines of evidence together, we estimate that the response of the Earth system to elevated atmospheric carbon dioxide concentrations is 30–50% greater than the response based on those fast-adjusting components of the climate system that are used traditionally to estimate climate sensitivity. We conclude that targets for the long-term stabilization of atmospheric greenhouse-gas concentrations aimed at preventing a dangerous human interference with the climate system should take into account this higher sensitivity of the Earth system.
- Published
- 2009
16. Comparison of mid-Pliocene climate predictions produced by the HadAM3 and GCMAM3 General Circulation Models
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Harry J. Dowsett, Alan M. Haywood, Paul J. Valdes, Mark A. Chandler, Daniel J. Lunt, and Ulrich Salzmann
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Global and Planetary Change ,Piacenzian ,010504 meteorology & atmospheric sciences ,Cloud cover ,Simulation modeling ,Biome ,Climate change ,Land cover ,15. Life on land ,010502 geochemistry & geophysics ,Oceanography ,01 natural sciences ,13. Climate action ,Climatology ,Pliocene climate ,Precipitation ,Geology ,0105 earth and related environmental sciences - Abstract
The mid-Pliocene warm period (ca. 3 to 3.3 million years ago) has become an important interval of time for palaeoclimate modelling exercises, with a large number of studies published during the last decade. However, there has been no attempt to assess the degree of model dependency of the results obtained. Here we present an initial comparison of mid-Pliocene climatologies produced by the Goddard Institute for Space Studies and Hadley Centre for Climate Prediction and Research atmosphere-only General Circulation Models (GCMAM3 and HadAM3). Whilst both models are consistent in the simulation of broad-scale differences in mid-Pliocene surface air temperature and total precipitation rates, significant variation is noted on regional and local scales. There are also significant differences in the model predictions of total cloud cover. A terrestrial data/model comparison, facilitated by the BIOME 4 model and a new data set of Piacenzian Stage land cover [Salzmann, U., Haywood, A.M., Lunt, D.J., Valdes, P.J., Hill, D.J., (2008). A new global biome reconstruction and data model comparison for the Middle Pliocene. Global Ecology and Biogeography 17, 432-447, doi:10.1111/j.1466-8238.2007.00381.x] and combined with the use of Kappa statistics, indicates that HadAM3-based biome predictions provide a closer fit to proxy data in the mid to high-latitudes. However, GCMAM3-based biomes in the tropics provide the closest fit to proxy data.
- Published
- 2009
17. Mid-Pliocene equatorial Pacific sea surface temperature reconstruction: a multi-proxy perspective
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Harry J. Dowsett and Marci M. Robinson
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Alkenone ,General Mathematics ,Ocean current ,Equator ,General Engineering ,General Physics and Astronomy ,Climate change ,Zonal and meridional ,Sea surface temperature ,Oceanography ,Greenhouse gas ,Climatology ,Environmental science ,Multi proxy - Abstract
The Mid-Pliocene is the most recent interval of sustained global warmth, which can be used to examine conditions predicted for the near future. An accurate spatial representation of the low-latitude Mid-Pliocene Pacific surface ocean is necessary to understand past climate change in the light of forecasts of future change. Mid-Pliocene sea surface temperature (SST) anomalies show a strong contrast between the western equatorial Pacific (WEP) and eastern equatorial Pacific (EEP) regardless of proxy (faunal, alkenone and Mg/Ca). All WEP sites show small differences from modern mean annual temperature, but all EEP sites show significant positive deviation from present-day temperatures by as much as 4.4°C. Our reconstruction reflects SSTs similar to modern in the WEP, warmer than modern in the EEP and eastward extension of the WEP warm pool. The east–west equatorial Pacific SST gradient is decreased, but the pole to equator gradient does not change appreciably. We find it improbable that increased greenhouse gases (GHG) alone would cause such a heterogeneous warming and more likely that the cause of Mid-Pliocene warmth is a combination of several forcings including both increased meridional heat transport and increased GHG.
- Published
- 2008
18. Introduction. Pliocene climate, processes and problems
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Bruce W. Sellwood, Alan M. Haywood, Jane E. Francis, Paul J. Valdes, Daniel J. Lunt, and Harry J. Dowsett
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Series (stratigraphy) ,Oceanography ,Ice core ,General Mathematics ,Climatology ,General Circulation Model ,General Engineering ,Pliocene climate ,General Physics and Astronomy ,Uniformitarianism ,Climate model ,Geologic record ,Geology - Abstract
Climate predictions produced by numerical climate models, often referred to as general circulation models (GCMs), suggest that by the end of the twenty-first century global mean annual surface air temperatures will increase by 1.1–6.4°C. Trace gas records from ice cores indicate that atmospheric concentrations of CO 2 are already higher than at any time during the last 650 000 years. In the next 50 years, atmospheric CO 2 concentrations are expected to reach a level not encountered since an epoch of time known as the Pliocene. Uniformitarianism is a key principle of geological science, but can the past also be a guide to the future? To what extent does an examination of the Pliocene geological record enable us to successfully understand and interpret this guide? How reliable are the ‘retrodictions’ of Pliocene climates produced by GCMs and what does this tell us about the accuracy of model predictions for the future? These questions provide the scientific rationale for this Theme Issue.
- Published
- 2008
19. Faunal re-evaluation of Mid-Pliocene conditions in the western equatorial Pacific
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Harry J. Dowsett
- Subjects
Marine isotope stage ,Sea surface temperature ,Paleothermometer ,Oceanography ,Climatology ,Interglacial ,Paleontology ,Upwelling ,Last Glacial Maximum ,Glacial period ,Neogene ,Geology - Abstract
Mid-Pliocene low-latitude Pacific faunal (planktic foraminifer) sea surface temperature (SST) estimates are normally based upon the Modern Analog Technique (MAT). In the Eastern equatorial Pacific (EEP), where upwelling of cool water predominates, MAT can be used to discern both cooling and warming in Neogene records. SST today is ~30°C in the western equatorial Pacific (WEP) warm pool, the upper limit of the modern calibration data, and past warming above that level is difficult to assess using faunal methods. Mid-Pliocene fossil samples from the WEP have been analyzed using several variations of MAT with different outcomes and associated levels of confidence. While SST above ~30°C in the WEP during the mid-Pliocene cannot be ruled out due to the limitations of the method, temperatures this warm seem unlikely. In addition to the mid-Pliocene, planktic foraminifer assemblages from the coretop, last glacial maximum, last interglacial and the penultimate glacial (Marine Isotope Stage 6) show striking similarity to each other which suggests little to no change in the region between times of global climate extremes. There is generally good agreement between the Mg/Ca paleothermometer and MAT derived faunal SST estimates. Both suggest stability of the WEP warm pool.
- Published
- 2007
20. Pliocene Model Intercomparison (PlioMIP) Phase 2: scientific objectives and experimental design
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Ulrich Salzmann, Matthew J. Pound, Alan M. Haywood, Mark A. Chandler, Daniel J. Lunt, Aisling M. Dolan, David B. Rowley, Bette L. Otto-Bliesner, Ayako Abe-Ouchi, Harry J. Dowsett, and Stephen J. Hunter
- Subjects
Coupled model intercomparison project ,Earth history ,Meteorology ,13. Climate action ,Climatology ,Paleoclimatology ,Climate change ,Environmental science ,F800 ,Atmospheric Model Intercomparison Project ,Climate model ,Context (language use) ,Future climate - Abstract
The Pliocene Model Intercomparison Project (PlioMIP) is a co-ordinated international climate modelling initiative to study and understand climate and environments of the Late Pliocene, and their potential relevance in the context of future climate change. PlioMIP operates under the umbrella of the Palaeoclimate Modelling Intercomparison Project (PMIP), which examines multiple intervals in Earth history, the consistency of model predictions in simulating these intervals and their ability to reproduce climate signals preserved in geological climate archives. This paper provides a thorough model intercomparison project description, and documents the experimental design in a detailed way. Specifically, this paper describes the experimental design and boundary conditions that will be utilised for the experiments in Phase 2 of PlioMIP.
- Published
- 2015
21. Climate variability from the Florida Bay sedimentary record: possible teleconnections to ENSO, PNA and CNP
- Author
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Sara B. Schwede, Thomas M. Cronin, C. D. Vann, Gary S. Dwyer, and Harry J. Dowsett
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Atmospheric Science ,Sediment ,Salinity ,Oceanography ,Geography ,North Atlantic oscillation ,Climatology ,Paleoclimatology ,Environmental Chemistry ,Paleosalinity ,Bay ,Relative species abundance ,General Environmental Science ,Teleconnection - Abstract
We analyzed decadal and interannual climate variability in South Florida since 1880 using geochemical and faunal paleosalinity indicators from isotopically dated sediment cores at Rus- sell Bank in Florida Bay (FB). Using the relative abundance of 2 ostracode species and the Mg/Ca ratios in Loxoconcha matagordensis shells to reconstruct paleosalinity, we found evidence for cyclic oscillations in the salinity of central FB. During this time salinity fluctuated from as low as ~18 parts per thousand (ppt) to as high as ~57 ppt. Time series analyses suggest, in addition to a 5.6 yr Mg/Ca based salinity periodicity, there are 3 other modes of variability in paleosalinity indicators: 6-7, 8-9, and 13-14 yr periods which occur in all paleo-proxies. To search for factors that might cause salinity to vary in FB, we compared the Russell Bank paleosalinity record to South Florida winter rainfall, the Southern Oscillation Index (SOI), winter North Atlantic Oscillation (NAO), and the winter Pacific North American (PNA) index, and a surrogate for the PNA in the winter season, the Central North Pacific (CNP) index. SOI and PNA/CNP appear to be associated with South Florida winter precipita- tion. Time series analyses of SOI and winter rainfall for the period 1910-1999 suggest ~5, 6-7, 8-9 and 13-14 yr cycles. The 6-7 yr and 13-14 yr cycles correspond to those observed in the faunal and geochemical time series from Russell Bank. The main periods of the CNP index are 5-6 and 13-15 yr, which are similar to those observed in FB paleosalinity. Cross-spectral analyses show that winter rainfall and salinity are coherent at 5.6 yr with a salinity lag of ~1.6 mo. These results suggest that regional rainfall variability influences FB salinity over interannual and decadal timescales and that much of this variability may have its origin in climate variability in the Pacific Ocean/atmosphere system.
- Published
- 2002
22. Can uncertainties in sea ice albedo reconcile patterns of data-model discord for the Pliocene and 20th/21st centuries?
- Author
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James Pope, Alan M. Haywood, Daniel J. Hill, Aisling M. Dolan, Harry J. Dowsett, Fergus W. Howell, Steven J. Pickering, Jane E. Francis, Ulrich Salzmann, and Bridget S. Wade
- Subjects
Arctic sea ice decline ,geography ,geography.geographical_feature_category ,010504 meteorology & atmospheric sciences ,Ice-albedo feedback ,Albedo ,F600 ,010502 geochemistry & geophysics ,01 natural sciences ,Arctic ice pack ,Arctic geoengineering ,Sea surface temperature ,Geophysics ,13. Climate action ,Climatology ,Sea ice ,General Earth and Planetary Sciences ,Environmental science ,Cryosphere ,0105 earth and related environmental sciences - Abstract
General Circulation Model simulations of the mid-Pliocene warm period (mPWP, 3.264 to 3.025 Myr ago) currently underestimate the level of warming that proxy data suggest existed at high latitudes, with discrepancies of up to 11°C for sea surface temperature estimates and 17°C for surface air temperature estimates. Sea ice has a strong influence on high-latitude climates, partly due to the albedo feedback. We present results demonstrating the effects of reductions in minimum sea ice albedo limits in general circulation model simulations of the mPWP. While mean annual surface air temperature increases of up to 6°C are observed in the Arctic, the maximum decrease in model-data discrepancies is just 0.81°C. Mean annual sea surface temperatures increase by up to 2°C, with a maximum model-data discrepancy improvement of 1.31°C. It is also suggested that the simulation of observed 21st century sea ice decline could be influenced by the adjustment of the sea ice albedo parameterization.
- Published
- 2014
23. Challenges in quantifying Pliocene terrestrial warming revealed by data–model discord
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Daniel J. Lunt, Alan M. Haywood, Hiroaki Ueda, Linda E. Sohl, Gerrit Lohmann, Nan Rosenbloom, Bette L. Otto-Bliesner, Ayako Abe-Ouchi, Wing-Le Chan, Aisling M. Dolan, Ulrich Salzmann, Gilles Ramstein, Jochen Voss, Zhongshi Zhang, Camille Contoux, Daniel J. Hill, Anne Jost, Mark A. Chandler, Fran Bragg, Steven J. Pickering, Matthew J. Pound, Christian Stepanek, Harry J. Dowsett, Youichi Kamae, University of Northumbria at Newcastle [United Kingdom], School of Earth and Environment [Leeds] (SEE), University of Leeds, Atmosphere and Ocean Research Institute [Kashiwa-shi] (AORI), The University of Tokyo (UTokyo), Structure et fonctionnement des systèmes hydriques continentaux (SISYPHE), Université Pierre et Marie Curie - Paris 6 (UPMC)-École Pratique des Hautes Études (EPHE), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Mines Paris - PSL (École nationale supérieure des mines de Paris), Université Paris sciences et lettres (PSL)-Centre National de la Recherche Scientifique (CNRS), Laboratoire des Sciences du Climat et de l'Environnement [Gif-sur-Yvette] (LSCE), Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS), Modélisation du climat (CLIM), Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS), Université Pierre et Marie Curie - Paris 6 (UPMC)-École pratique des hautes études (EPHE), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-MINES ParisTech - École nationale supérieure des mines de Paris, Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ), and Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)
- Subjects
[SDU.OCEAN]Sciences of the Universe [physics]/Ocean, Atmosphere ,010504 meteorology & atmospheric sciences ,Biome ,Global warming ,Northern Hemisphere ,Climate change ,Environmental Science (miscellaneous) ,010502 geochemistry & geophysics ,Atmospheric temperature ,01 natural sciences ,Proxy (climate) ,13. Climate action ,Climatology ,Pliocene climate ,Climate model ,[SDU.ENVI]Sciences of the Universe [physics]/Continental interfaces, environment ,Social Sciences (miscellaneous) ,Geology ,ComputingMilieux_MISCELLANEOUS ,0105 earth and related environmental sciences - Abstract
Comparing simulations of key warm periods in Earth history with contemporaneous geological proxy data is a useful approach for evaluating the ability of climate models to simulate warm, high-CO2 climates that are unprecedented in the more recent past. Here we use a global data set of confidence-assessed, proxy-based temperature estimates and biome reconstructions to assess the ability of eight models to simulate warm terrestrial climates of the Pliocene epoch. The Late Pliocene, 3.6–2.6 million years ago, is an accessible geological interval to understand climate processes of a warmer world. We show that model-predicted surface air temperatures reveal a substantial cold bias in the Northern Hemisphere. Particularly strong data–model mismatches in mean annual temperatures (up to 18 °C) exist in northern Russia. Our model sensitivity tests identify insufficient temporal constraints hampering the accurate configuration of model boundary conditions as an important factor impacting on data–model discrepancies. We conclude that to allow a more robust evaluation of the ability of present climate models to predict warm climates, future Pliocene data–model comparison studies should focus on orbitally defined time slices.
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- 2013
24. On the identification of a Pliocene time slice for data-model comparison
- Author
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James Pope, Erin L McClymont, Paul J. Valdes, Aisling M. Dolan, Daniel J. Hill, Ulrich Salzmann, Alan M. Haywood, Daniel J. Lunt, Steven J. Pickering, Harry J. Dowsett, Caroline L. Prescott, and Stephen J. Hunter
- Subjects
Marine isotope stage ,010504 meteorology & atmospheric sciences ,Meteorology ,Orbital forcing ,ARCTIC-OCEAN ,Pliocene ,General Mathematics ,SEA-SURFACE TEMPERATURES ,ICE-SHEET ,EXPERIMENTAL-DESIGN ,General Physics and Astronomy ,Present day ,F600 ,010502 geochemistry & geophysics ,BOUNDARY-CONDITIONS ,01 natural sciences ,Proxy (climate) ,Meteorology and Climatology ,climate models ,MIDDLE PLIOCENE ,GENERAL-CIRCULATION MODEL ,0105 earth and related environmental sciences ,geography ,geography.geographical_feature_category ,Excursion ,General Engineering ,Earth system sensitivity ,Articles ,JOINT INVESTIGATIONS ,WARM PERIOD ,INSOLATION QUANTITIES ,13. Climate action ,Climatology ,Earth Sciences ,Climate sensitivity ,climate sensitivity ,Climate model ,Ice sheet ,Geology ,Research Article - Abstract
The characteristics of the mid-Pliocene warm period (mPWP: 3.264–3.025 Ma BP) have been examined using geological proxies and climate models. While there is agreement between models and data, details of regional climate differ. Uncertainties in prescribed forcings and in proxy data limit the utility of the interval to understand the dynamics of a warmer than present climate or evaluate models. This uncertainty comes, in part, from the reconstruction of a time slab rather than a time slice , where forcings required by climate models can be more adequately constrained. Here, we describe the rationale and approach for identifying a time slice(s) for Pliocene environmental reconstruction. A time slice centred on 3.205 Ma BP (3.204–3.207 Ma BP) has been identified as a priority for investigation. It is a warm interval characterized by a negative benthic oxygen isotope excursion (0.21–0.23‰) centred on marine isotope stage KM5c (KM5.3). It occurred during a period of orbital forcing that was very similar to present day. Climate model simulations indicate that proxy temperature estimates are unlikely to be significantly affected by orbital forcing for at least a precession cycle centred on the time slice, with the North Atlantic potentially being an important exception.
- Published
- 2013
25. Sea surface temperature of the mid-Piacenzian ocean: A data-model comparison
- Author
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Camille Contoux, Wing-Le Chan, Christian Stepanek, J. Jonas, Zhongshi Zhang, Gilles Ramstein, Alan M. Haywood, Kerim H. Nisancioglu, Danielle K. Stoll, Marci M. Robinson, Harry J. Dowsett, Youichi Kamae, Hiroaki Ueda, Gerrit Lohmann, Qing Yan, Stephanie L. Strother, Bette L. Otto-Bliesner, Christina R. Riesselman, Aisling M. Dolan, Anne Jost, Mats Bentsen, Kevin M. Foley, Ayako Abe-Ouchi, Fran Bragg, Linda E. Sohl, Ulrich Salzmann, Nan Rosenbloom, Mark A. Chandler, Daniel J. Lunt, United States Geological Survey [Reston] (USGS), NASA Goddard Institute for Space Studies (GISS), NASA Goddard Space Flight Center (GSFC), National Center for Atmospheric Research [Boulder] (NCAR), Structure et fonctionnement des systèmes hydriques continentaux (SISYPHE), Université Pierre et Marie Curie - Paris 6 (UPMC)-École pratique des hautes études (EPHE), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-MINES ParisTech - École nationale supérieure des mines de Paris, Université Paris sciences et lettres (PSL)-Centre National de la Recherche Scientifique (CNRS), Laboratoire des Sciences du Climat et de l'Environnement [Gif-sur-Yvette] (LSCE), Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ), Modélisation du climat (CLIM), Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ), Japan Agency for Marine-Earth Science and Technology (JAMSTEC), University of Northumbria at Newcastle [United Kingdom], Institute of Atmospheric Physics [Beijing] (IAP), Chinese Academy of Sciences [Beijing] (CAS), Université Pierre et Marie Curie - Paris 6 (UPMC)-École Pratique des Hautes Études (EPHE), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Mines Paris - PSL (École nationale supérieure des mines de Paris), Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS), and Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)
- Subjects
Marine biology ,010506 paleontology ,Multidisciplinary ,Piacenzian ,010504 meteorology & atmospheric sciences ,Climate change ,F700 ,Biology ,F600 ,Bioinformatics ,01 natural sciences ,Article ,Sea surface temperature ,13. Climate action ,Policy decision ,[SDU.STU.CL]Sciences of the Universe [physics]/Earth Sciences/Climatology ,Climatology ,Climate model ,14. Life underwater ,Data model (GIS) ,[SDU.STU.PG]Sciences of the Universe [physics]/Earth Sciences/Paleontology ,0105 earth and related environmental sciences - Abstract
International audience; The mid-Piacenzian climate represents the most geologically recent interval of long-term average warmth relative to the last million years, and shares similarities with the climate projected for the end of the 21st century. As such, it represents a natural experiment from which we can gain insight into potential climate change impacts, enabling more informed policy decisions for mitigation and adaptation. Here, we present the first systematic comparison of Pliocene sea surface temperature (SST) between an ensemble of eight climate model simulations produced as part of PlioMIP (Pliocene Model Intercomparison Project) with the PRISM (Pliocene Research, Interpretation and Synoptic Mapping) Project mean annual SST field. Our results highlight key regional and dynamic situations where there is discord between the palaeoenvironmental reconstruction and the climate model simulations. These differences have led to improved strategies for both experimental design and temporal refinement of the palaeoenvironmental reconstruction.
- Published
- 2013
26. Large-scale features of Pliocene climate: results from the Pliocene Model Intercomparison Project
- Author
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Gilles Ramstein, Ayako Abe-Ouchi, Wing-Le Chan, Camille Contoux, Harry J. Dowsett, Youichi Kamae, Mark A. Chandler, Qing Yan, Ulrich Salzmann, Linda E. Sohl, Christian Stepanek, Nan Rosenbloom, Gerrit Lohmann, Alan M. Haywood, Daniel J. Hill, Anne Jost, Aisling M. Dolan, Daniel J. Lunt, Zhongshi Zhang, Hiroaki Ueda, Bette L. Otto-Bliesner, Fran Bragg, Steven J. Pickering, School of Earth and Environment [Leeds] (SEE), University of Leeds, National Center for Atmospheric Research [Boulder] (NCAR), School of Geographical Sciences [Bristol], University of Bristol [Bristol], Atmosphere and Ocean Research Institute [Kashiwa-shi] (AORI), The University of Tokyo (UTokyo), NASA Goddard Institute for Space Studies (GISS), NASA Goddard Space Flight Center (GSFC), Structure et fonctionnement des systèmes hydriques continentaux (SISYPHE), Université Pierre et Marie Curie - Paris 6 (UPMC)-École Pratique des Hautes Études (EPHE), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Mines Paris - PSL (École nationale supérieure des mines de Paris), Université Paris sciences et lettres (PSL)-Centre National de la Recherche Scientifique (CNRS), Laboratoire des Sciences du Climat et de l'Environnement [Gif-sur-Yvette] (LSCE), Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS), Modélisation du climat (CLIM), Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS), Université Pierre et Marie Curie - Paris 6 (UPMC)-École pratique des hautes études (EPHE), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-MINES ParisTech - École nationale supérieure des mines de Paris, Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ), and Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)
- Subjects
010504 meteorology & atmospheric sciences ,Orbital forcing ,Stratigraphy ,lcsh:Environmental protection ,Climate change ,F600 ,010502 geochemistry & geophysics ,01 natural sciences ,lcsh:Environmental pollution ,Paleoclimatology ,Pliocene climate ,lcsh:TD169-171.8 ,[SDU.ENVI]Sciences of the Universe [physics]/Continental interfaces, environment ,lcsh:Environmental sciences ,ComputingMilieux_MISCELLANEOUS ,0105 earth and related environmental sciences ,lcsh:GE1-350 ,[SDU.OCEAN]Sciences of the Universe [physics]/Ocean, Atmosphere ,Global and Planetary Change ,Paleontology ,Earth system science ,13. Climate action ,Climatology ,lcsh:TD172-193.5 ,Polar amplification ,Climate sensitivity ,Climate model ,Geology - Abstract
Climate and environments of the mid-Pliocene warm period (3.264 to 3.025 Ma) have been extensively studied. Whilst numerical models have shed light on the nature of climate at the time, uncertainties in their predictions have not been systematically examined. The Pliocene Model Intercomparison Project quantifies uncertainties in model outputs through a coordinated multi-model and multi-model/data intercomparison. Whilst commonalities in model outputs for the Pliocene are clearly evident, we show substantial variation in the sensitivity of models to the implementation of Pliocene boundary conditions. Models appear able to reproduce many regional changes in temperature reconstructed from geological proxies. However, data/model comparison highlights that models potentially underestimate polar amplification. To assert this conclusion with greater confidence, limitations in the time-averaged proxy data currently available must be addressed. Furthermore, sensitivity tests exploring the known unknowns in modelling Pliocene climate specifically relevant to the high latitudes are essential (e.g. palaeogeography, gateways, orbital forcing and trace gasses). Estimates of longer-term sensitivity to CO2 (also known as Earth System Sensitivity; ESS), support previous work suggesting that ESS is greater than Climate Sensitivity (CS), and suggest that the ratio of ESS to CS is between 1 and 2, with a "best" estimate of 1.5.
- Published
- 2013
- Full Text
- View/download PDF
27. Simulations of the Mid-Pliocene Warm Period using the NASA/GISS ModelE2-R Earth System Model
- Author
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J. Jonas, L. E. Sohl, Harry J. Dowsett, and Mark A. Chandler
- Subjects
Climatology ,Period (geology) ,Earth system model ,Atmospheric sciences ,Geology - Abstract
Climate reconstructions of the mid-Pliocene Warm Period (mPWP) bear many similarities to aspects of future global warming as projected by the Intergovernmental Panel on Climate Change. In particular, marine and terrestrial paleoclimate data point to high latitude temperature amplification, with associated decreases in sea ice and land ice and altered vegetation distributions that show expansion of warmer climate biomes into higher latitudes. NASA GISS climate models have been used to study the Pliocene climate since the USGS PRISM project first identified that the mid-Pliocene North Atlantic sea surface temperatures were anomalously warm. Here we present the most recent simulations of the Pliocene using the AR5/CMIP5 version of the GISS Earth System Model known as ModelE2-R. These simulations constitute the NASA contribution to the Pliocene Model Intercomparison Project (PlioMIP) Experiment 2. Many findings presented here corroborate results from other PlioMIP multi-model ensemble papers, but we also emphasize features in the ModelE2-R simulations that are unlike the ensemble means. We provide discussion of features that show considerable improvement compared with simulations from previous versions of the NASA GISS models, improvement defined here as simulation results that more closely resemble the ocean core data as well as the PRISM3D reconstructions of the mid-Pliocene climate. In some regions even qualitative agreement between model results and paleodata are an improvement over past studies, but the dramatic warming in the North Atlantic and Greenland-Iceland-Norwegian Sea in these new simulations is by far the most accurate portrayal ever of this key geographic region by the GISS climate model. Our belief is that continued development of key physical routines in the atmospheric model, along with higher resolution and recent corrections to mixing parameterizations in the ocean model, have led to an Earth System Model that will produce more accurate projections of future climate.
- Published
- 2012
28. Assessing confidence in Pliocene sea surface temperatures to evaluate predictive models
- Author
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Marci M. Robinson, Danielle K. Stoll, Kevin M. Foley, Christina R. Riesselman, Alan M. Haywood, Aisling M. Dolan, Wing-Le Chan, Harry J. Dowsett, Bette L. Otto-Bliesner, Mark A. Chandler, Daniel J. Hill, Ayako Abe-Ouchi, Daniel J. Lunt, Nan Rosenbloom, and Fran Bragg
- Subjects
Ground truth ,010504 meteorology & atmospheric sciences ,Climate oscillation ,Global warming ,Climate change ,Environmental Science (miscellaneous) ,010502 geochemistry & geophysics ,01 natural sciences ,Sea surface temperature ,13. Climate action ,Climatology ,Paleoclimatology ,Pliocene climate ,Environmental science ,Climate model ,14. Life underwater ,Social Sciences (miscellaneous) ,0105 earth and related environmental sciences - Abstract
Sea-surface-temperature proxy data for a period of natural climate warming during the Pliocene are used in this study to show how palaeoclimatic data can help ‘ground truth’ numerical models, increasing the confidence in these same models for projecting future climate.
- Published
- 2012
- Full Text
- View/download PDF
29. Pliocene climate variability over glacial-interglacial timescales (PlioVAR) working group
- Author
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Harry J. Dowsett, Erin L McClymont, Alan M. Haywood, Petra Dekens, Lydie M Dupont, Antoni Rosell-Melé, and Ulrich Salzmann
- Subjects
Group (stratigraphy) ,Climatology ,Interglacial ,Pliocene climate ,Physical geography ,Glacial period ,Geology - Published
- 2015
30. Pliocene three-dimensional global ocean temperature reconstruction
- Author
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Harry J. Dowsett, Marci M. Robinson, and Kevin M. Foley
- Subjects
lcsh:GE1-350 ,Global and Planetary Change ,Water mass ,Stratigraphy ,lcsh:Environmental protection ,North Atlantic Deep Water ,Paleontology ,Bottom water ,Oceanography ,Antarctic Bottom Water ,lcsh:Environmental pollution ,Circumpolar deep water ,Climatology ,lcsh:TD172-193.5 ,Deep ocean water ,Pliocene climate ,Thermohaline circulation ,lcsh:TD169-171.8 ,Geology ,lcsh:Environmental sciences - Abstract
The thermal structure of the mid-Piacenzian ocean is obtained by combining the Pliocene Research, Interpretation and Synoptic Mapping Project (PRISM3) multiproxy sea-surface temperature (SST) reconstruction with bottom water temperature estimates from 27 locations produced using Mg/Ca paleothermometry based upon the ostracod genus Krithe. Deep water temperature estimates are skewed toward the Atlantic Basin (63% of the locations) and represent depths from 1000 m to 4500 m. This reconstruction, meant to serve as a validation data set as well as an initialization for coupled numerical climate models, assumes a Pliocene water mass framework similar to that which exists today, with several important modifications. The area of formation of present day North Atlantic Deep Water (NADW) was expanded and extended further north toward the Arctic Ocean during the mid-Piacenzian relative to today. This, combined with a deeper Greenland-Scotland Ridge, allowed a greater volume of warmer NADW to enter the Atlantic Ocean. In the Southern Ocean, the Polar Front Zone was expanded relative to present day, but shifted closer to the Antarctic continent. This, combined with at least seasonal reduction in sea ice extent, resulted in decreased Antarctic Bottom Water (AABW) production (relative to present day) as well as possible changes in the depth of intermediate waters. The reconstructed mid-Piacenzian three-dimensional ocean was warmer overall than today, and the hypothesized aerial extent of water masses appears to fit the limited stable isotopic data available for this time period.
- Published
- 2009
31. Impact of a permanent El Niño (El Padre) and Indian Ocean Dipole in warm Pliocene climates
- Author
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Kenneth D. Mankoff, Harry J. Dowsett, Sonali P. Shukla, J. Jonas, Linda E. Sohl, and Mark A. Chandler
- Subjects
Convection ,Sea surface temperature ,Oceanography ,El Niño ,Global distribution ,General Circulation Model ,Climatology ,Paleontology ,Precipitation ,Indian Ocean Dipole ,Geology - Abstract
[1] Pliocene sea surface temperature data, as well as terrestrial precipitation and temperature proxies, indicate warmer than modern conditions in the eastern equatorial Pacific and imply permanent El Nino–like conditions with impacts similar to those of the 1997/1998 El Nino event. Here we use a general circulation model to examine the global-scale effects that result from imposing warm tropical sea surface temperature (SST) anomalies in both modern and Pliocene simulations. Observed SSTs from the 1997/1998 El Nino event were used for the anomalies and incorporate Pacific warming as well as a prominent Indian Ocean Dipole event. Both the permanent El Nino (also called El Padre) and Indian Ocean Dipole (IOD) conditions are necessary to reproduce temperature and precipitation patterns consistent with the global distribution of Pliocene proxy data. These patterns may result from the poleward propagation of planetary waves from the strong convection centers associated with the El Nino and IOD.
- Published
- 2009
32. Pliocene sea surface temperatures of the north atlantic ocean at 3.0 Ma
- Author
-
Harry J. Dowsett and Richard Z. Poore
- Subjects
Archeology ,Global and Planetary Change ,Orbital forcing ,Ocean current ,Geology ,Deep sea ,Sea surface temperature ,Oceanography ,Stage (stratigraphy) ,Climatology ,Atlantic multidecadal oscillation ,Interglacial ,Pliocene climate ,Ecology, Evolution, Behavior and Systematics - Abstract
Sea-surface temperature (SST) estimates based on quantitative analysis of planktic foraminifer faunas in North Atlantic deep sea cores suggest that high-frequency, low-amplitude variability related to orbital forcing was superimposed on long-term changes that delineate intervals within the Pliocene that were both warmer and cooler than today. SST estimates from several DSDP and ODP sites, as well as land sections, have been combined into a synoptic view of SST during a Pliocene warm interval centered at about 3.0 Ma. The Pliocene North Atlantic warm interval SST estimates show little evidence for warming in tropical regions whereas mid- to high-latitude areas show moderate to strong warming. SST estimates for the last interglacial (Isotope Stage 5e) show a similar pattern, but warming during the last interglacial was not as pronounced as the Middle Pliocene warming. The regional distribution of SST estimates during these past warm events suggests an increase in ocean circulation.
- Published
- 1991
33. Surface temperatures of the Mid-Pliocene North Atlantic Ocean: implications for future climate
- Author
-
Harry J. Dowsett, Marci M. Robinson, and Mark A. Chandler
- Subjects
General Mathematics ,Global warming ,General Engineering ,General Physics and Astronomy ,Climate change ,Oceanography ,Atlantic Equatorial mode ,Effects of global warming ,Climatology ,Atlantic multidecadal oscillation ,Abrupt climate change ,Climate model ,Thermohaline circulation ,Geology - Abstract
The Mid-Pliocene is the most recent interval in the Earth's history to have experienced warming of the magnitude predicted for the second half of the twenty-first century and is, therefore, a possible analogue for future climate conditions. With continents basically in their current positions and atmospheric CO 2 similar to early twenty-first century values, the cause of Mid-Pliocene warmth remains elusive. Understanding the behaviour of the North Atlantic Ocean during the Mid-Pliocene is integral to evaluating future climate scenarios owing to its role in deep water formation and its sensitivity to climate change. Under the framework of the Pliocene Research, Interpretation and Synoptic Mapping (PRISM) sea surface reconstruction, we synthesize Mid-Pliocene North Atlantic studies by PRISM members and others, describing each region of the North Atlantic in terms of palaeoceanography. We then relate Mid-Pliocene sea surface conditions to expectations of future warming. The results of the data and climate model comparisons suggest that the North Atlantic is more sensitive to climate change than is suggested by climate model simulations, raising the concern that estimates of future climate change are conservative.
- Published
- 2008
34. Reevaluation of mid-Pliocene North Atlantic sea surface temperatures
- Author
-
Gary S. Dwyer, Marci M. Robinson, Harry J. Dowsett, and Kira T Lawrence
- Subjects
Alkenone ,Paleontology ,Drilling ,Climate change ,Extinct species ,Seasonality ,Oceanography ,medicine.disease ,Deep sea ,Sea surface temperature ,Climatology ,medicine ,Geology ,Faunal assemblage - Abstract
[1] Multiproxy temperature estimation requires careful attention to biological, chemical, physical, temporal, and calibration differences of each proxy and paleothermometry method. We evaluated mid-Pliocene sea surface temperature (SST) estimates from multiple proxies at Deep Sea Drilling Project Holes 552A, 609B, 607, and 606, transecting the North Atlantic Drift. SST estimates derived from faunal assemblages, foraminifer Mg/Ca, and alkenone unsaturation indices showed strong agreement at Holes 552A, 607, and 606 once differences in calibration, depth, and seasonality were addressed. Abundant extinct species and/or an unrecognized productivity signal in the faunal assemblage at Hole 609B resulted in exaggerated faunal-based SST estimates but did not affect alkenone-derived or Mg/Ca–derived estimates. Multiproxy mid-Pliocene North Atlantic SST estimates corroborate previous studies documenting high-latitude mid-Pliocene warmth and refine previous faunal-based estimates affected by environmental factors other than temperature. Multiproxy investigations will aid SST estimation in high-latitude areas sensitive to climate change and currently underrepresented in SST reconstructions.
- Published
- 2008
35. A new planktic foraminifer transfer function for estimating pliocene—Holocene paleoceanographic conditions in the North Atlantic
- Author
-
Richard Z. Poore and Harry J. Dowsett
- Subjects
Sea surface temperature ,Oceanography ,Stable isotope ratio ,Climatology ,Northern Hemisphere ,Paleontology ,Detritus (geology) ,Glacial period ,Surface water ,Deep sea ,Geology ,Holocene - Abstract
A new planktic foraminifer transfer function (GSF18) related 5 North Atlantic assemblages to winter and summer sea surface temperature. GSF18, based on recombined and simplified core top census data, preserves most environmental information and reproduces modern North Atlantic conditions with approximately the same accuracy as previous transfer functions, but can be more readily applied to faunal samples ranging in age from Pliocene to Holocene. Transfer function GSF18 has been applied to faunal data from Deep Sea Drilling Project Hole 552A to produce a 2.5 m.y. sea-surface temperature (SST) time series. Estimates show several periods between 2.3 and 4.6 Ma during which mean SST's were both several degrees warmer and several degrees cooler than modern conditions. Between 2.9 and 4.0 Ma SST was generally warmer than modern except for a 250 k.y. interval centered at 3.3 Ma. Maximum SST, with respect to modern conditions, occurred after the cool interval near 3.1 Ma when SST was approximately 3.6°C warmer than present conditions. Comparison of SST estimates with stable isotope data suggest that after peak warming at 3.1 Ma, there was an overall surface water cooling with concomitant build up of global ice volume, culminating in Northern Hemisphere glaciation. This event is also indicated by the presence of ice rafted detritus in 552A sediments at about 2.45 Ma.
- Published
- 1990
36. Middle Pliocene sea surface temperature variability
- Author
-
Harry J. Dowsett, Mark A. Chandler, Gary S. Dwyer, and Thomas M. Cronin
- Subjects
biology ,Paleontology ,Magnitude (mathematics) ,Forcing (mathematics) ,Oceanography ,biology.organism_classification ,Spatial distribution ,Sea surface temperature ,Diatom ,Ostracod ,Climatology ,Error bar ,Period (geology) ,Geology - Abstract
[1] Estimates of sea surface temperature (SST) based upon foraminifer, diatom, and ostracod assemblages from ocean cores reveal a warm phase of the Pliocene between about 3.3 and 3.0 Ma. Pollen records and plant megafossils, although not as well dated, show evidence for a warmer climate at about the same time. Increased greenhouse forcing and altered ocean heat transport are the leading candidates for the underlying cause of Pliocene global warmth. Despite being a period of global warmth, this interval encompasses considerable variability. Two new SST reconstructions are presented that are designed to provide a climatological error bar for warm peak phases of the Pliocene and to document the spatial distribution and magnitude of SST variability within the mid-Pliocene warm period. These data suggest long-term stability of low-latitude SST and document greater variability in regions of maximum warming.
- Published
- 2005
37. Bracketing mid-pliocene sea surface temperature: maximum and minimum possible warming
- Author
-
Harry J. Dowsett
- Subjects
Sea surface temperature ,Error bar ,Climatology ,Period (geology) ,Forcing (mathematics) ,Land based ,Atmospheric sciences ,Geology - Abstract
Estimates of sea surface temperature (SST) from ocean cores reveal a warm phase of the Pliocene between about 3.3 and 3.0 Megaannum’s (Ma). Pollen records from land based cores and sections, although not as well dated, also show evidence for a warmer climate at about the same time. Increased greenhouse forcing and altered ocean heat transport is the leading candidates for the underlying cause of Pliocene global warmth. However, despite being a period of global warmth, there exists considerable variability within this interval. Two new SST reconstructions have been created to provide a climatological error bar for warm peak phases of the Pliocene. These data represent the maximum and minimum possible warming recorded within the 3.3 to 3.0 Ma interval.
- Published
- 2004
38. Gulf of Mexico planktic foraminifer transfer function GOM2: preliminary report
- Author
-
Stacey Verardo, Richard Z. Poore, and Harry J. Dowsett
- Subjects
Oceanography ,Preliminary report ,Climatology ,Geology - Published
- 2003
39. Gulf of Mexico planktic foraminifer core-top calibration data set: Raw data
- Author
-
Richard Z. Poore, Stacey Verardo, Charlotte A. Brunner, and Harry J. Dowsett
- Subjects
Core (optical fiber) ,Data set ,Calibration (statistics) ,Climatology ,Geology - Published
- 2003
40. Climate model simulations of the mid-Pliocene: Earth's last great interval of global warmth
- Author
-
Aisling M. Dolan, Alan M. Haywood, and Harry J. Dowsett
- Subjects
Paleoclimate Modelling Intercomparison Project ,Climatology ,Geological survey ,General Earth and Planetary Sciences ,Climate model ,Context (language use) ,Geology - Abstract
Pliocene Model Intercomparison Project Workshop; Reston, Virginia, 2–4 August 2011 The Pliocene Model Intercomparison Project (PlioMIP), supported by the U.S. Geological Survey's (USGS) Pliocene Research, Interpretation and Synoptic Mapping (PRISM) project and Powell Center, is an integral part of a third iteration of the Paleoclimate Modelling Intercomparison Project (PMIP3). PlioMIP's aim is to systematically compare structurally different climate models. This is done in the context of the mid-Pliocene (∼3.3–3.0 million years ago), a geological interval when the global annual mean temperature was similar to predictions for the next century.
- Published
- 2012
41. PRISM 8 degrees X 10 degrees North Hemisphere paleoclimate reconstruction; digital data
- Author
-
John A. Barron, Thomas R. Holtz, Debra A. Willard, Richard Z. Poore, Farley R. Fleming, Thomas M. Cronin, Robert S. Thompson, Harry J. Dowsett, and Scott E. Ishman
- Subjects
Geography ,Climatology ,Paleoclimatology ,Digital data ,Prism ,Geodesy - Published
- 1994
42. Pliocene Role in Assessing Future Climate Impacts
- Author
-
Mark A. Chandler, Harry J. Dowsett, and Marci M. Robinson
- Subjects
Runaway climate change ,business.industry ,Global warming ,Environmental resource management ,Climate commitment ,Climate change ,Effects of global warming ,Climatology ,Abrupt climate change ,General Earth and Planetary Sciences ,Environmental science ,Climate sensitivity ,Climate state ,business - Abstract
Future warming projected by the Intergovernmental Panel on Climate Change (IPCC) has the potential to affect every person on Earth. Extreme weather events, rising sea level, and migrating ecosystems and resources may result in socioeconomic stresses. Although we can plan and prepare for what is expected, the most dangerous aspect of our changing climate is the uncertainty in climate sensitivity. To reduce the uncertainties of climate change, paleoclimatologists are focusing on a possible yet imperfect analog to a future warmer climate.
- Published
- 2008
43. The pliocene record of climatic change: equator-to-pole biotic response
- Author
-
Harry J. Dowsett and Thomas M. Cronin
- Subjects
Climatology ,Equator ,Climate change ,Geology - Abstract
Pliocene faunal events in tropical and subtropical regions of the Americas and the Caribbean have been causally linked to global climatic events, particularly, progressive cooling and increased amplitude of climatic cycles between 3.5 and 2.0 Ma. However, the rate and magnitude of Pliocene temperature changes has been determined in only a few climate proxy records. Our study contrasts paleoceanographic conditions at 3 Ma, an extremely warm period in many areas, with conditions 2.4 Ma, a much cooler interval, in equator-to-pole transects for the North Atlantic and the North Pacific Oceans. By using microfaunal data (ostracodes from ocean margin environments and planktic foraminifers from deep sea cores), quantitative factor analytic and modern analog dissimilarity coefficient analyses were carried out on faunas from the following sections.Our studies lead to the following conclusions: (1) Equator-to-pole thermal gradients in the oceans at 3.0 Ma were not as steep as they are today, but thermal gradients at 2.4 Ma were steeper than those today; (2)At 3 Ma middle to high latitudes were substantially warmer than today, but tropical regions were about the same; (3)Substantial cooling occurred in middle and high latitudes in the western North Pacific Ocean and the western North Atlantic between 3 Ma and 2.4 Ma; (4)Ocean water temperatures off the southeastern U.S. remained the same or cooled only slightly between 3 Ma and 2.4 Ma. Our results support the hypothesis that ocean circulation changes, probably resulting from the closure of near surface water by the Isthmus of Panama, had significant impact on equator-to-pole heat transport and global climate between about 3 and 2.4 Ma. They also argue against the hypothesis that climatically induced ocean temperature changes were directly linked to a major marine extinction in the southwestern North Atlantic and Caribbean.
- Published
- 1992
44. Modelling the enigmatic Late Pliocene Glacial Event — Marine Isotope Stage M2
- Author
-
Harry J. Dowsett, Steven J. Pickering, Julia Tindall, Stephen J. Hunter, Alan M. Haywood, Daniel J. Hill, and Aisling M. Dolan
- Subjects
Global and Planetary Change ,geography ,geography.geographical_feature_category ,Pliocene ,Climate oscillation ,Oceanography ,Arctic ice pack ,Ice-sheet model ,Ice core ,Climatology ,Ice age ,Cryosphere ,Glacial ,Climate state ,Marine Isotope Stage M2 ,Ice sheets ,Ice sheet ,Geology ,HadCM3 - Abstract
The Pliocene Epoch (5.2 to 2.58 Ma) has often been targeted to investigate the nature of warm climates. However, climate records for the Pliocene exhibit significant variability and show intervals that apparently experienced a cooler than modern climate. Marine Isotope Stage (MIS) M2 (~ 3.3 Ma) is a globally recognisable cooling event that disturbs an otherwise relatively (compared to present-day) warm background climate state. It remains unclear whether this event corresponds to significant ice sheet build-up in the Northern and Southern Hemisphere. Estimates of sea level for this interval vary, and range from modern values to estimates of 65 m sea level fall with respect to present day. Here we implement plausible M2 ice sheet configurations into a coupled atmosphere–ocean climate model to test the hypothesis that larger-than-modern ice sheet configurations may have existed at M2. Climate model results are compared with proxy climate data available for M2 to assess the plausibility of each ice sheet configuration. Whilst the outcomes of our data/model comparisons are not in all cases straight forward to interpret, there is little indication that results from model simulations in which significant ice masses have been prescribed in the Northern Hemisphere are incompatible with proxy data from the North Atlantic, Northeast Arctic Russia, North Africa and the Southern Ocean. Therefore, our model results do not preclude the possibility of the existence of larger ice masses during M2 in the Northern or Southern Hemisphere. Specifically they are not able to discount the possibility of significant ice masses in the Northern Hemisphere during the M2 event, consistent with a global sea-level fall of between 40 m and 60 m. This study highlights the general need for more focused and coordinated data generation in the future to improve the coverage and consistency in proxy records for M2, which will allow these and future M2 sensitivity tests to be interrogated further.
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