38 results on '"Singarayer, Joy S."'
Search Results
2. Environmental conditions do not predict diversification rates in the Bantu languages
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Beyer, Robert, Singarayer, Joy S., Stock, Jay T., and Manica, Andrea
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- 2019
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3. Niche dynamics of Palaeolithic modern humans during the settlement of the Palaearctic
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Giampoudakis, Konstantinos, Marske, Katharine A., Borregaard, Michael K., Ugan, Andrew, Singarayer, Joy S., Valdes, Paul J., Rahbek, Carsten, and Nogués-Bravo, David
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- 2017
4. Reconstructing paleosalinity from δ18O: Coupled model simulations of the Last Glacial Maximum, Last Interglacial and Late Holocene
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Holloway, Max D., Sime, Louise C., Singarayer, Joy S., Tindall, Julia C., and Valdes, Paul J.
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- 2016
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5. Explaining patterns of avian diversity and endemicity: climate and biomes of southern Africa over the last 140,000 years
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Huntley, Brian, Collingham, Yvonne C., Singarayer, Joy S., Valdes, Paul J., Barnard, Phoebe, Midgley, Guy F., Altwegg, Res, and Ohlemüller, Ralf
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- 2016
6. Interhemispheric dynamics of the African rainbelt during the late Quaternary
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Singarayer, Joy S. and Burrough, Sallie L.
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- 2015
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7. Microbial community dynamics in the forefield of glaciers
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Bradley, James A., Singarayer, Joy S., and Anesio, Alexandre M.
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- 2014
8. Global biome patterns of the Middle and Late Pleistocene.
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Huntley, Brian, Allen, Judy R. M., Forrest, Matthew, Hickler, Thomas, Ohlemüller, Ralf, Singarayer, Joy S., and Valdes, Paul J.
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ATMOSPHERIC carbon dioxide ,LEAF area index ,BIOMES ,PLEISTOCENE Epoch ,RAIN forests ,CLIMATE change - Abstract
Our primary aim was to assess the hypothesis that distinctive features of the patterns of vegetation change during successive Quaternary glacial–interglacial cycles reflect climatic differences arising from forcing differences. We addressed this hypothesis using 207 half‐degree resolution global biome pattern simulations, for time slices between 800 and 2 ka, made using the LPJ‐GUESS dynamic global vegetation model. Simulations were driven using ice‐core atmospheric CO2 concentrations, Earth's obliquity, and outputs from a pre‐industrial and 206 palaeoclimate experiments; four additional simulations were driven using projected future CO2 concentrations. Climate experiments were run using HadCM3. Using a rule‐based approach, above‐ground biomass and leaf area index of LPJ‐GUESS plant functional types were used to infer each grid cell's biome. The hypothesis is supported by the palaeobiome simulations. To enable comparisons with the climatic forcing, multivariate analyses were performed of global vegetation pattern dissimilarities between simulations. Results showed generally similar responses to glacial–interglacial climatic variations during each cycle, although no two interglacials or glacials had identical biome patterns. Atmospheric CO2 concentration was the strongest driver of the dissimilarity patterns. Dissimilarities relative to the time slice with the lowest atmospheric CO2 concentration show the log‐linear relationship to atmospheric CO2 concentration expected of an index of ecocarbon sensitivity. For each simulation, extent and total above‐ground biomass of each biome were calculated globally and for three longitudinal segments corresponding to the major continental regions. Mean and minimum past extents of forest biomes, notably Temperate Summergreen Forest, in the three major continental regions strongly parallel relative tree diversities, hence supporting the hypothesis that past biome extents played an important role in determining present diversity. Albeit that they reflect the climatic consequences only of the faster Earth system components, simulated potential future biome patterns are unlike any during the past 800 ky, and likely will continue to change markedly for millennia if projected CO2 concentrations are realised. [ABSTRACT FROM AUTHOR]
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- 2023
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9. Late Pleistocene climate change and the global expansion of anatomically modern humans
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Eriksson, Anders, Betti, Lia, Friend, Andrew D., Lycett, Stephen J., Singarayer, Joy S., von Cramon-Taubadel, Noreen, Valdes, Paul J., Balloux, Francois, and Manica, Andrea
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- 2012
10. Response of Amazonian forests to mid-Holocene drought: a model-data comparison
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Smith, Richard J., Singarayer, Joy S., and Mayle, Francis E.
- Abstract
There is major concern for the fate of Amazonia over the coming century in the face of anthropogenic climate change. A key area of uncertainty is the scale of rainforest die-back to be expected under a future, drier climate. In this study, we use the middle Holocene (ca. 6,000 years before present) as an approximate analogue for a drier future, given that palaeoclimate data show much of Amazonia was significantly drier than present at this time. Here, we use an ensemble of climate and vegetation models to explore the sensitivity of Amazonian biomes to mid-Holocene climate change. For this we employ three dynamic vegetation models (JULES, IBIS, and SDGVM) forced by the bias-corrected mid-Holocene climate simulations from seven models that participated in the Paleoclimate Modelling Intercomparison Project 3 (PMIP3). These model outputs are compared with a multi-proxy palaeoecological dataset to gain a better understanding of where in Amazonia we have most confidence in the mid-Holocene vegetation simulations. A robust feature of all simulations and palaeodata is that the central Amazonian rainforest biome is unaffected by mid-Holocene drought. Greater divergence in mid-Holocene simulations exists in ecotonal eastern and southern Amazonia. Vegetation models driven with climate models that simulate a drier mid Holocene (100-150 mm per year decrease) better capture the observed (palaeodata) tropical forest die-back in these areas. Based on the relationship between simulated rainfall decrease and vegetation change, we find indications that in southern Amazonia the rate of tropical forest die-back was ~125,000 km2 per 100 mm rainfall decrease in the mid Holocene. This provides a baseline sensitivity of tropical forests to drought for this region (without human-driven changes to greenhouse gases, fire, and deforestation). We highlight the need for more palaeoecological and palaeoclimate data across lowland Amazonia to constrain model responses.
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- 2021
11. Twenty-First-Century Climate Impacts from a Declining Arctic Sea Ice Cover
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Singarayer, Joy S., Bamber, Jonathan L., and Valdes, Paul J.
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- 2006
12. Last glacial vegetation of northern Eurasia
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Allen, Judy R.M., Hickler, Thomas, Singarayer, Joy S., Sykes, Martin T., Valdes, Paul J., and Huntley, Brian
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- 2010
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13. High-latitude climate sensitivity to ice-sheet forcing over the last 120 kyr
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Singarayer, Joy S. and Valdes, Paul J.
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- 2010
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14. The fate of the Caspian Sea under projected climate change and water extraction during the 21st century
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Koriche, Sifan A., Singarayer, Joy S., and Cloke, Hannah L.
- Abstract
The Caspian Sea (CS) delivers considerable ecosystem services to millions of people. It experienced water level variations of 3 m during the 20th century alone. Robust scenarios of future CS level are vital to inform environmental risk management and water-use planning. In this study we investigated the water budget variation in the CS drainage basin and its potential impact on CS level during the 21st century using projected climate from selected climate change scenarios of shared socioeconomic pathways (SSPs) and representative concentration pathways (RCPs), and explored the impact of human extractions. We show that the size of the CS prescribed in climate models determines the modelled water budgets for both historical and future projections. Most future projections show drying over the 21st century. The moisture deficits are more pronounced for extreme radiative forcing scenarios (RCP8.5/SSP585) and for models where a larger CS is prescribed. By 2100, up to 8 (10) m decrease in CS level is found using RCP4.5 (RCP8.5) models, and up to 20 (30) m for SSP245 (SSP585) scenario models. Water extraction rates are as important as climate in controlling future CS level, with potentially up to 7 m further decline, leading to desiccation of the shallow northern CS. This will have wide-ranging implications for the livelihoods of the surrounding communities; increasing vulnerability to freshwater scarcity, transforming ecosystems, as well as impacting the climate system. Caution should be exercised when using individual models to inform policy as projected CS level is so variable between models. We identify that many climate models either ignore, or do not properly prescribe, CS area. No future climate projections include any changes in CS surface area, even when the catchment is projected to be considerably drier. Coupling between atmosphere and lakes within climate models would be a significant advance to capture crucial two-way feedbacks.
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- 2021
15. Late Quaternary highstands at Lake Chilwa, Malawi: Frequency, timing and possible forcing mechanisms in the last 44 ka
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Thomas, David S.G., Bailey, Richard, Shaw, Paul A., Durcan, Julie A., and Singarayer, Joy S.
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- 2009
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16. Late Quaternary hydrological dynamics in the Middle Kalahari: Forcing and feedbacks
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Burrough, Sallie L., Thomas, David S.G., and Singarayer, Joy S.
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- 2009
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17. Late Holocene methane rise caused by orbitally controlled increase in tropical sources
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Singarayer, Joy S., Valdes, Paul J., Friedlingstein, Pierre, and Beerling, Sarah Nelson David J.
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Atmospheric chemistry -- Research -- Environmental aspects -- Chemical properties ,Methane -- Environmental aspects -- Chemical properties -- Research ,Environmental issues ,Science and technology ,Zoology and wildlife conservation - Abstract
Considerable debate surrounds the source of the apparently 'anomalous' (1) increase of atmospheric methane concentrations since the mid-Holocene (5,000 years ago) compared to previous interglacial periods as recorded in polar ice core records (2). Proposed mechanisms for the rise in methane concentrations relate either to methane emissions from anthropogenic early rice cultivation (1,3) or an increase in natural wetland emissions from tropical (4) or boreal sources (5,6). Here we show that our climate and wetland simulations of the global methane cycle over the last glacial cycle (the past 130,000 years) recreate the ice core record and capture the late Holocene increase in methane concentrations. Our analyses indicate that the late Holocene increase results from natural changes in the Earth's orbital configuration, with enhanced emissions in the Southern Hemisphere tropics linked to precession-induced modification of seasonal precipitation. Critically, our simulations capture the declining trend in methane concentrations at the end of the last interglacial period (115,000-130,000 years ago) that was used to diagnose the Holocene methane rise as unique. The difference between the two time periods results from differences in the size and rate of regional insolation changes and the lack of glacial inception in the Holocene. Our findings also suggest that no early agricultural sources are required to account for the increase in methane concentrations in the 5,000 years before the industrial era., Atmospheric methane (C[H.sub.4]) is a strong greenhouse gas influenced by various natural (for example, wetlands, biomass burning) and anthropogenic (for example, rice agriculture, enhanced biomass burning, landfill) sources (7). The [...]
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- 2011
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18. Species-specific responses of Late Quaternary megafauna to climate and humans
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Lorenzen, Eline D., Nogués-Bravo, David, Orlando, Ludovic, Weinstock, Jaco, Binladen, Jonas, Marske, Katharine A., Ugan, Andrew, Borregaard, Michael K., Gilbert, Thomas M. P., Nielsen, Rasmus, Ho, Simon Y. W., Goebel, Ted, Graf, Kelly E., Byers, David, Stenderup, Jesper T., Rasmussen, Morten, Campos, Paula F., Leonard, Jennifer A., Koepfli, Klaus-Peter, Froese, Duane, Zazula, Grant, Stafford, Thomas W., Aaris-Sørensen, Kim, Batra, Persaram, Haywood, Alan M., Singarayer, Joy S., Valdes, Paul J., Boeskorov, Gennady, Burns, James A., Davydov, Sergey P., Haile, James, Jenkins, Dennis L., Kosintsev, Pavel, Kuznetsova, Tatyana, Lai, Xulong, Martin, Larry D., McDonald, Gregory H., Mol, Dick, Meldgaard, Morten, Munch, Kasper, Stephan, Elisabeth, Sablin, Mikhail, Sommer, Robert S., Sipko, Taras, Scott, Eric, Suchard, Marc A., Tikhonov, Alexei, Willerslev, Rane, Wayne, Robert K., Cooper, Alan, Hofreiter, Michael, Sher, Andrei, Shapiro, Beth, Rahbek, Carsten, and Willerslev, Eske
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- 2011
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19. Ocean dominated expansion and contraction of the late Quaternary tropical rainbelt
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Singarayer, Joy S., Valdes, Paul J., and Roberts, William H.G.
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lcsh:R ,lcsh:Medicine ,lcsh:Q ,lcsh:Science - Abstract
The latitude of the tropical rainbelt oscillates seasonally but has also varied on millennial time-scales in response to changes in the seasonal distribution of insolation due to Earth’s orbital configuration, as well as climate change initiated at high latitudes. Interpretations of palaeoclimate proxy archives often suggest hemispherically coherent variations, some proposing meridional shifts in global rainbelt position and the ‘global monsoon’, while others propose interhemispherically symmetric expansion and contraction. Here, we use a unique set of climate model simulations of the last glacial cycle (120 kyr), that compares well against a compilation of precipitation proxy data, to demonstrate that while asymmetric extratropical forcings (icesheets, freshwater hosing) generally produce meridional shifts in the zonal mean rainbelt, orbital variations produce expansion/contractions in terms of the global zonal mean. This is primarily a dynamic response of the rainbelt over the oceans to regional interhemispheric temperature gradients, which is opposite to the largely local thermodynamic terrestrial response to insolation. The mode of rainbelt variation is regionally variable, depending on surface type (land or ocean) and surrounding continental configuration. This makes interpretation of precipitation-proxy records as large-scale rainbelt movement challenging, requiring regional or global data syntheses.
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- 2017
20. Response of Amazonian forests to mid‐Holocene drought: A model‐data comparison.
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Smith, Richard J., Singarayer, Joy S., and Mayle, Francis E.
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FOREST declines , *EFFECT of human beings on climate change , *TROPICAL forests , *PALEOECOLOGY , *DROUGHT management , *DROUGHTS , *ATMOSPHERIC models , *RAIN forests - Abstract
There is a major concern for the fate of Amazonia over the coming century in the face of anthropogenic climate change. A key area of uncertainty is the scale of rainforest dieback to be expected under a future, drier climate. In this study, we use the middle Holocene (ca. 6000 years before present) as an approximate analogue for a drier future, given that palaeoclimate data show much of Amazonia was significantly drier than present at this time. Here, we use an ensemble of climate and vegetation models to explore the sensitivity of Amazonian biomes to mid‐Holocene climate change. For this, we employ three dynamic vegetation models (JULES, IBIS, and SDGVM) forced by the bias‐corrected mid‐Holocene climate simulations from seven models that participated in the Palaeoclimate Modelling Intercomparison Project 3 (PMIP3). These model outputs are compared with a multi‐proxy palaeoecological dataset to gain a better understanding of where in Amazonia we have most confidence in the mid‐Holocene vegetation simulations. A robust feature of all simulations and palaeodata is that the central Amazonian rainforest biome is unaffected by mid‐Holocene drought. Greater divergence in mid‐Holocene simulations exists in ecotonal eastern and southern Amazonia. Vegetation models driven with climate models that simulate a drier mid‐Holocene (100–150 mm per year decrease) better capture the observed (palaeodata) tropical forest dieback in these areas. Based on the relationship between simulated rainfall decrease and vegetation change, we find indications that in southern Amazonia the rate of tropical forest dieback was ~125,000 km2 per 100 mm rainfall decrease in the mid‐Holocene. This provides a baseline sensitivity of tropical forests to drought for this region (without human‐driven changes to greenhouse gases, fire, and deforestation). We highlight the need for more palaeoecological and palaeoclimate data across lowland Amazonia to constrain model responses. [ABSTRACT FROM AUTHOR]
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- 2022
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21. Projected climatic changes lead to biome changes in areas of previously constant biome.
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Huntley, Brian, Allen, Judy R. M., Forrest, Matthew, Hickler, Thomas, Ohlemüller, Ralf, Singarayer, Joy S., Valdes, Paul J., and Williams, Jack
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CLIMATE change ,BIOMES ,CARBON sequestration ,SPECIES diversity ,ECOSYSTEM services - Abstract
Aim: Recent studies in southern Africa identified past biome stability as an important predictor of biodiversity. We aimed to assess the extent to which past biome stability predicts present global biodiversity patterns, and the extent to which projected climatic changes may lead to eventual biome changes in areas with constant past biome. Location: Global. Taxon: Spermatophyta; terrestrial vertebrates. Methods: Biome constancy was assessed and mapped using results from 89 dynamic global vegetation model simulations, driven by outputs of palaeoclimate experiments spanning the past 140 ka. We tested the hypothesis that terrestrial vertebrate diversity is predicted by biome constancy. We also simulated potential future vegetation, and hence potential future biome patterns, and quantified and mapped the extent of projected eventual future biome change in areas of past constant biome. Results: Approximately 11% of global ice‐free land had a constant biome since 140 ka. Apart from areas of constant Desert, many areas with constant biome support high species diversity. All terrestrial vertebrate groups show a strong positive relationship between biome constancy and vertebrate diversity in areas of greater diversity, but no relationship in less diverse areas. Climatic change projected by 2100 commits 46%–66% of global ice‐free land, and 34%–52% of areas of past constant biome (excluding areas of constant Desert) to eventual biome change. Main conclusions: Past biome stability strongly predicts vertebrate diversity in areas of higher diversity. Future climatic changes will lead to biome changes in many areas of past constant biome, with profound implications for biodiversity conservation. Some projected biome changes will result in substantial reductions in biospheric carbon sequestration and other ecosystem services. [ABSTRACT FROM AUTHOR]
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- 2021
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22. Impacts of Variations in Caspian Sea Surface Area on Catchment‐Scale and Large‐Scale Climate.
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Koriche, Sifan A., Nandini‐Weiss, Sri D., Prange, Matthias, Singarayer, Joy S., Arpe, Klaus, Cloke, Hannah L., Schulz, Michael, Bakker, Pepijn, Leroy, Suzanne A. G., and Coe, Michael
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SEA level ,SURFACE area ,WATERSHEDS ,ATMOSPHERIC models - Abstract
The Caspian Sea (CS) is the largest inland lake in the world. Large variations in sea level and surface area occurred in the past and are projected for the future. The potential impacts on regional and large‐scale hydroclimate are not well understood. Here, we examine the impact of CS area on climate within its catchment and across the northern hemisphere, for the first time with a fully coupled climate model. The Community Earth System Model (CESM1.2.2) is used to simulate the climate of four scenarios: (a) larger than present CS area, (b) current area, (c) smaller than present area, and (d) no‐CS scenario. The results reveal large changes in the regional atmospheric water budget. Evaporation (e) over the sea increases with increasing area, while precipitation (P) increases over the south‐west CS with increasing area. P‐E over the CS catchment decreases as CS surface area increases, indicating a dominant negative lake‐evaporation feedback. A larger CS reduces summer surface air temperatures and increases winter temperatures. The impacts extend eastwards, where summer precipitation is enhanced over central Asia and the north‐western Pacific experiences warming with reduced winter sea ice. Our results also indicate weakening of the 500‐hPa troughs over the northern Pacific with larger CS area. We find a thermal response triggers a southward shift of the upper troposphere jet stream during summer. Our findings establish that changing CS area results in climate impacts of such scope that CS area variations should be incorporated into climate model simulations, including palaeo and future scenarios. Plain Language Summary: The Caspian Sea is the largest land‐locked water body in the world. It is filled by rivers draining a vast region from northern Russia to Iran. The size of the Caspian Sea has varied considerably over recent centuries and millennia due to various factors, including changes in climate. Conversely, as the area of the sea changes it also has impacts on the climate, but there are significant questions about how and where those impacts would be felt. In this study we used a state‐of‐the‐art climate model in which we specified different sizes of Caspian Sea in order to examine how the climate changes as its area increases. We observed that the local seasonal cycle of temperatures gets smaller, and evaporation increases, while there are more spatially complex changes in local rainfall. Furthermore, the impacts on atmospheric circulation occur as far as the north Pacific, with resulting increases in temperature and decreases in sea‐ice coverage in winter as the Caspian area increases. The climate impacts are so significant and geographically extensive that climate models used to simulate climate change (both in future and past scenarios) should incorporate changes to the Caspian Sea area if they are to robustly model regional climate. Key Points: Surface water budget over the Caspian catchment decreases as surface area increases due to negative lake surface‐evaporation feedbackA larger Caspian Sea enhances precipitation over central Asia, warms the north‐western Pacific during winter, and reduces Pacific sea iceAccurate representation of the Caspian Sea in climate models is important to avoid creating additional biases both locally and globally [ABSTRACT FROM AUTHOR]
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- 2021
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23. Simulating the 128 ka Antarctic climate response to Northern Hemisphere ice sheet melting using the isotope-enabled HadCM3
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Holloway, Max D., Sime, Louise C., Singarayer, Joy S., Tindall, Julia C., and Valdes, Paul J.
- Abstract
Warmer than present Antarctic and Southern Ocean temperatures during the last interglacial, approximately 128,000 years ago, have been attributed to changes in north-south ocean heat transport, causing opposing hemispheric temperature anomalies. We investigate the magnitude of Antarctic warming and Antarctic ice core isotopic enrichment in response to Northern Hemisphere meltwater input during the early last interglacial. A 1,600 year HadCM3 simulation driven by 0.25 Sv of meltwater input reproduces 50-60 % of the peak Southern Ocean summer sea surface temperature anomaly, sea ice retreat and ice core isotope enrichment. We also find a robust increase in the proportion of cold season precipitation during the last interglacial, leading to lower isotopic values at the Antarctic ice core sites. These results suggest that a HadCM3 simulation including 0.25 Sv for 3,000-4,000 years would reconcile the last interglacial observations, providing a potential solution for the last interglacial 'missing heat' problem.
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- 2018
24. Global vegetation patterns of the past 140,000 years.
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Allen, Judy R. M., Forrest, Matthew, Hickler, Thomas, Singarayer, Joy S., Valdes, Paul J., and Huntley, Brian
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VEGETATION patterns ,LEAF area index ,LAST Glacial Maximum ,TROPICAL forests ,GRID cells - Abstract
Aim: Insight into global biome responses to climatic and other environmental changes is essential to address key questions about past and future impacts of such changes. By simulating global biome patterns 140 ka to present, we aimed to address important questions about biome changes during this interval. Location: Global. Taxon: Spermatophyta. Methods: Using the LPJ‐GUESS dynamic global vegetation model, we made 89 simulations driven using ice‐core atmospheric CO2 concentrations, Earth's obliquity, and outputs from a pre‐industrial and 88 palaeoclimate experiments run using HadCM3. Experiments were run for 81 time slices between 1 and 140 ka, seven 'hosing' experiments also being run, using a 1‐Sv freshwater flux to the North Atlantic, for time slices corresponding to Heinrich Events H0–H6. Using a rule‐based approach, based on carbon mass and leaf area index of the LPJ‐GUESS plant functional types, the biome was inferred for each grid cell. Biomes were mapped, and the extent and total vegetation biomass of each biome, and total global vegetation biomass, estimated. Results: Substantial changes in biome extents and locations were found on all vegetated continents. Although the largest magnitude changes were in Eurasia, important changes were seen in tropical latitudes and the Southern Hemisphere. Total global extent of most biomes varied on multi‐millennial (orbital) time scales, although some (e.g. Tropical Raingreen Forest) responded principally to the c. 100‐kyr glacial–interglacial cycle and others (e.g. Temperate Broad‐leaved Evergreen Forest) mainly to the c. 20‐kyr precession cycle. Many also responded to millennial contrasts between stadial ('hosing') and interstadial climates, with some (e.g. Tropical Evergreen Forest) showing stronger responses than to the multi‐millennial changes. Main conclusions: No two time slices had identical biome patterns. Even equivalent Holocene and last interglacial time slices, and the last and penultimate glacial maxima, showed important differences. Only a small proportion of global land area experienced no biome change since 140 ka; many places experienced multiple biome changes. These modelling experiments provided little evidence for long‐term biome stability. [ABSTRACT FROM AUTHOR]
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- 2020
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25. CMIP6/PMIP4 simulations of the mid-Holocene and Last Interglacial using HadGEM3: comparison to the pre-industrial era, previous model versions and proxy data.
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Williams, Charles J. R., Guarino, Maria-Vittoria, Capron, Emilie, Malmierca-Vallet, Irene, Singarayer, Joy S., Sime, Louise C., Lunt, Daniel J., and Valdes, Paul J.
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OCEAN temperature ,RADIATIVE forcing ,PROXY ,CLIMATE change ,INDUSTRIAL pollution ,CYCLOSTRATIGRAPHY ,GREENHOUSE gases - Abstract
Palaeoclimate model simulations are an important tool to improve our understanding of the mechanisms of climate change. These simulations also provide tests of the ability of models to simulate climates very different to today. Here we present the results from two brand-new simulations using the latest version of the UK's physical climate model, HadGEM3-GC3.1; they are the mid-Holocene (∼6 ka) and Last Interglacial (∼127 ka) simulations, both conducted under the auspices of CMIP6/PMIP4. This is the first time this version of the UK model has been used to conduct palaeoclimate simulations. These periods are of particular interest to PMIP4 because they represent the two most recent warm periods in Earth history, where atmospheric concentration of greenhouse gases and continental configuration are similar to the pre-industrial period but where there were significant changes to the Earth's orbital configuration, resulting in a very different seasonal cycle of radiative forcing. Results for these simulations are assessed firstly against the same model's pre-industrial control simulation (a simulation comparison, to describe and understand the differences between the pre-industrial – PI – and the two palaeo simulations) and secondly against previous versions of the same model relative to newly available proxy data (a model–data comparison, to compare all available simulations from the same model with proxy data to assess any improvements due to model advances). The introduction of this newly available proxy data adds further novelty to this study. Globally, for metrics such as 1.5 m temperature and surface rainfall, whilst both the recent palaeoclimate simulations are mostly capturing the expected sign and, in some places, magnitude of change relative to the pre-industrial, this is geographically and seasonally dependent. Compared to newly available proxy data (including sea surface temperature – SST – and rainfall) and also incorporating data from previous versions of the model shows that the relative accuracy of the simulations appears to vary according to metric, proxy reconstruction used for comparison and geographical location. In some instances, such as mean rainfall in the mid-Holocene, there is a clear and linear improvement, relative to proxy data, from the oldest to the newest generation of the model. When zooming into northern Africa, a region known to be problematic for models in terms of rainfall enhancement, the behaviour of the West African monsoon in both recent palaeoclimate simulations is consistent with current understanding, suggesting a wetter monsoon during the mid-Holocene and (more so) the Last Interglacial, relative to the pre-industrial era. However, regarding the well-documented "Saharan greening" during the mid-Holocene, results here suggest that the most recent version of the UK's physical model is still unable to reproduce the increases suggested by proxy data, consistent with all other previous models to date. [ABSTRACT FROM AUTHOR]
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- 2020
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26. The UK contribution to CMIP6/PMIP4: mid-Holocene and Last Interglacial experiments with HadGEM3, and comparison to the pre-industrial era and proxy data.
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Williams, Charles J. R., Guarino, Maria-Vittoria, Capron, Emilie, Malmierca-Vallet, Irene, Singarayer, Joy S., Sime, Louise C., Lunt, Daniel J., and Valdes, Paul J.
- Abstract
Palaeoclimate model simulations are an important tool to improve our understanding of the mechanisms of climate change. These simulations also provide tests of the ability of models to simulate climates very different to today. Here we present the results from two simulations using the latest version of the UK's physical climate model, HadGEM3-GC3.1; the mid-Holocene (~ 6 ka) and Last Interglacial (~ 127 ka) simulations, both conducted under the auspices of CMIP6/PMIP4. These periods are of particular interest to PMIP4 because they represent the two most recent warm periods in Earth history, where atmospheric concentration of greenhouse gases and continental configuration is similar to the pre-industrial period but where there were significant changes to the Earth's orbital configuration, resulting in a very different seasonal cycle of radiative forcing. Results for these simulations are assessed against proxy data, previous versions of the UK model, and models from the previous CMIP5 exercise. When the current version is compared to the previous generation of the UK model, the most recent version suggests limited improvement. In common with these previous model versions, the simulations reproduce global land and ocean temperatures (both surface and at 1.5 m) and a West African monsoon that is consistent with the latitudinal and seasonal distribution of insolation. The Last Interglacial simulation appears to accurately capture Northern Hemisphere temperature changes, but without the addition of Last Interglacial meltwater forcing cannot capture the magnitude of Southern Hemisphere changes. Model-data comparisons indicate that some geographical regions, and some seasons, produce better matches to the palaeodata (relative to pre-industrial) than others. Model-model comparisons, relative to previous generations same model and other models, indicate similarity between generations in terms of both the intensity and northward enhancement of the mid-Holocene West African monsoon, both of which are underestimated. On the "Saharan greening" which occurred the mid-Holocene African Humid Period, simulation results are likewise consistent with other models. The most recent version of the UK model appears to still be unable to reproduce the amount of rainfall necessary to support grassland across the Sahara. [ABSTRACT FROM AUTHOR]
- Published
- 2020
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27. The role of CO2 and dynamic vegetation on the impact of temperate land use change in the HadCM3 coupled climate model
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Armstrong, Edward, Valdes, Paul, House, Jo, and Singarayer, Joy S.
- Abstract
Human induced land-use change (LUC) alters the biogeophysical characteristics of the land surface influencing the surface energy balance. The level of atmospheric CO2 is expected to increase in the coming century and beyond, modifying temperature and precipitation patterns and altering the distribution and physiology of natural vegetation. It is important to constrain how CO2-induced climate and vegetation change may influence the regional extent to which LUC alters climate. This sensitivity study uses the HadCM3 coupled climate model under a range of equilibrium forcings to show that the impact of LUC declines under increasing atmospheric CO2, specifically in temperate and boreal regions. A surface energy balance analysis is used to diagnose how these changes occur. In Northern Hemisphere winter this pattern is attributed in part to the decline in winter snow cover and in the summer due to a reduction in latent cooling with higher levels of CO2. The CO2-induced change in natural vegetation distribution is also shown to play a significant role. Simulations run at elevated CO2 yet present day vegetation show a significantly increased sensitivity to LUC, driven in part by an increase in latent cooling. This study shows that modelling the impact of LUC needs to accurately simulate CO2 driven changes in precipitation and snowfall, and incorporate accurate, dynamic vegetation distribution.
- Published
- 2016
28. Sea-surface temperature records of Termination 1 in the Gulf of California: Challenges for seasonal and interannual analogues of tropical Pacific climate change
- Author
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Mcclymont, Erin L., Ganeshram, Raja S., Pichevin, Laetitia, Talbot, Helen M., Van Dongen, Bart E., Thunell, Robert C., Haywood, Alan M., Singarayer, Joy S., and Valdes, Paul J.
- Subjects
GDGT ,tropical Pacific ,sea-surface temperature ,alkenone ,climate modeling ,terminations - Abstract
Centennial-scale records of sea-surface temperature and opal composition spanning the Last Glacial Maximum and Termination 1 (circa 25-6 ka) are presented here from Guaymas Basin in the Gulf of California. Through the application of two organic geochemistry proxies, the U-37(K') index and the TEX86H index, we present evidence for rapid, stepped changes in temperatures during deglaciation. These occur in both temperature proxies at 13 ka (similar to 3 degrees C increase in 270 years), 10.0 ka (similar to 2 degrees C decrease over similar to 250 years) and at 8.2 ka (3 degrees C increase in
- Published
- 2012
29. Towards radiocarbon calibration beyond 28 ka using speleothems from the Bahamas
- Author
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Hoffmann, Dirk L., Beck, J. Warren, Richards, David A., Smart, Peter L., Singarayer, Joy S., Ketchmark, Tricia, and Hawkesworth, Chris J.
- Published
- 2010
- Full Text
- View/download PDF
30. EOF analysis of three records of sea-ice concentration spanning the last 30 years
- Author
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Singarayer, Joy S.
- Abstract
Several continuous observational datasets of Artic sea-ice concentration are currently available that cover the period since the advent of routine satellite observations. We report on a comparison of three sea-ice concentration datasets. These are the National Ice Center charts, and two passive microwave radiometer datasets derived using different approaches: the NASA team and Bootstrap algorithms. Empirical orthogonal function (EOF) analyses were employed to compare modes of variability and their consistency between the datasets. The analysis was motivated by the need for a reliable, realistic sea ice climatology for use in climate model simulations, for which both the variability and absolute values of extent and concentration are important. We found that, while there are significant discrepancies in absolute concentrations, the major modes of variability derived from all records were essentially the same.
- Published
- 2003
31. Impact of meltwater on high-latitude early Last Interglacial climate.
- Author
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Stone, Emma J., Capron, Emilie, Lunt, Daniel J., Payne, Antony J., Singarayer, Joy S., Valdes, Paul J., and Wolff, Eric W.
- Subjects
MELTWATER ,INTERGLACIALS ,CLIMATOLOGY ,ICE sheets - Abstract
Recent data compilations of the early Last Interglacial period have indicated a bipolar temperature response at 130 ka, with colder-than-present temperatures in the North Atlantic and warmer-than-present temperatures in the Southern Ocean and over Antarctica. However, climate model simulations of this period have been unable to reproduce this response, when only orbital and greenhouse gas forcings are considered in a climate model framework. Using a full-complexity general circulation model we perform climate model simulations representative of 130 ka conditions which include a magnitude of freshwater forcing derived from data at this time. We show that this meltwater from the remnant Northern Hemisphere ice sheets during the glacial- interglacial transition produces a modelled climate response similar to the observed colder-than-present temperatures in the North Atlantic at 130 ka and also results in warmer-thanpresent temperatures in the Southern Ocean via the bipolar seesaw mechanism. Further simulations in which the West Antarctic Ice Sheet is also removed lead to warming in East Antarctica and the Southern Ocean but do not appreciably improve the model-data comparison. This integrated model- data approach provides evidence that Northern Hemisphere freshwater forcing is an important player in the evolution of early Last Interglacial climate. [ABSTRACT FROM AUTHOR]
- Published
- 2016
- Full Text
- View/download PDF
32. The biogeophysical climatic impacts of anthropogenic land use change during the Holocene.
- Author
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Smith, M. Clare, Singarayer, Joy S., Valdes, Paul J., Kaplan, Jed O., and Branch, Nicholas P.
- Subjects
EFFECT of human beings on climate change ,LAND use ,HOLOCENE Epoch ,BIOGEOCHEMICAL cycles ,DEFORESTATION ,PASTURES - Abstract
The first agricultural societies were established around 10 ka BP and had spread across much of Europe and southern Asia by 5.5 ka BP with resultant anthropogenic deforestation for crop and pasture land. Various studies (e.g. Joos et al., 2004; Kaplan et al., 2011; Mitchell et al., 2013) have attempted to assess the biogeochemical implications for Holocene climate in terms of increased carbon dioxide and methane emissions. However, less work has been done to examine the biogeophysical impacts of this early land use change. In this study, global climate model simulations with Hadley Centre Coupled Model version 3 (HadCM3) were used to examine the biogeophysical effects of Holocene land cover change on climate, both globally and regionally, from the early Holocene (8 ka BP) to the early industrial era (1850 CE). Two experiments were performed with alternative descriptions of past vegetation: (i) one in which potential natural vegetation was simulated by Top-down Representation of Interactive Foliage and Flora Including Dynamics (TRIFFID) but without land use changes and (ii) one where the anthropogenic land use model Kaplan and Krumhardt 2010 (KK10; Kaplan et al., 2009, 2011) was used to set the HadCM3 crop regions. Snapshot simulations were run at 1000-year intervals to examine when the first signature of anthropogenic climate change can be detected both regionally, in the areas of land use change, and globally. Results from our model simulations indicate that in regions of early land disturbance such as Europe and south-east Asia detectable temperature changes, outside the normal range of variability, are encountered in the model as early as 7 ka BP in the June-July- August (JJA) season and throughout the entire annual cycle by 2-3 ka BP. Areas outside the regions of land disturbance are also affected, with virtually the whole globe experiencing significant temperature changes (predominantly cooling) by the early industrial period. The global annual mean temperature anomalies found in our single model simulations were -0.22 at 1850 CE,-0.11 at 2 ka BP, and-0.03 ±C at 7 ka BP. Regionally, the largest temperature changes were in Europe with anomalies of -0.83 at 1850 CE, -0.58 at 2 ka BP, and -0.24 °C at 7 ka BP. Large-scale precipitation features such as the Indian monsoon, the Intertropical Convergence Zone (ITCZ), and the North Atlantic storm track are also impacted by local land use and remote teleconnections. We investigated how advection by surface winds, mean sea level pressure (MSLP) anomalies, and tropospheric stationary wave train disturbances in the mid- to high latitudes led to remote teleconnections. [ABSTRACT FROM AUTHOR]
- Published
- 2016
- Full Text
- View/download PDF
33. Robustness despite uncertainty: regional climate data reveal the dominant role of humans in explaining global extinctions of Late Quaternary megafauna.
- Author
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Bartlett, Lewis J., Williams, David R., Prescott, Graham W., Balmford, Andrew, Green, Rhys E., Eriksson, Anders, Valdes, Paul J., Singarayer, Joy S., and Manica, Andrea
- Subjects
CLIMATOLOGY ,DATA analysis ,DESCRIPTIVE statistics ,ECOLOGICAL succession ,ECOLOGY - Abstract
Debate over the Late Quaternary megafaunal extinctions has focussed on whether human colonisation or climatic changes were more important drivers of extinction, with few extinctions being unambiguously attributable to either. Most analyses have been geographically or taxonomically restricted and the few quantitative global analyses have been limited by coarse temporal resolution or overly simplified climate reconstructions or proxies. We present a global analysis of the causes of these extinctions which uses high-resolution climate reconstructions and explicitly investigates the sensitivity of our results to uncertainty in the palaeological record. Our results show that human colonisation was the dominant driver of megafaunal extinction across the world but that climatic factors were also important. We identify the geographic regions where future research is likely to have the most impact, with our models reliably predicting extinctions across most of the world, with the notable exception of mainland Asia where we fail to explain the apparently low rate of extinction found in in the fossil record. Our results are highly robust to uncertainties in the palaeological record, and our main conclusions are unlikely to change qualitatively following minor improvements or changes in the dates of extinctions and human colonisation. [ABSTRACT FROM AUTHOR]
- Published
- 2016
- Full Text
- View/download PDF
34. Assessing the benefits of crop albedo bio-geoengineering.
- Author
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Singarayer, Joy S, Ridgwell, Andy, and Irvine, Peter
- Published
- 2009
- Full Text
- View/download PDF
35. Tackling Regional Climate Change By Leaf Albedo Bio-geoengineering
- Author
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Ridgwell, Andy, Singarayer, Joy S., Hetherington, Alistair M., and Valdes, Paul J.
- Subjects
- *
CLIMATE change , *GLOBAL warming , *GREENHOUSE gases , *SOLAR radiation , *ALBEDO , *REFLECTANCE , *AGRICULTURAL climatology , *BIOENERGETICS - Abstract
Summary: The likelihood that continuing greenhouse-gas emissions will lead to an unmanageable degree of climate change has stimulated the search for planetary-scale technological solutions for reducing global warming (“geoengineering”), typically characterized by the necessity for costly new infrastructures and industries . We suggest that the existing global infrastructure associated with arable agriculture can help, given that crop plants exert an important influence over the climatic energy budget because of differences in their albedo (solar reflectivity) compared to soils and to natural vegetation . Specifically, we propose a “bio-geoengineering” approach to mitigate surface warming, in which crop varieties having specific leaf glossiness and/or canopy morphological traits are specifically chosen to maximize solar reflectivity. We quantify this by modifying the canopy albedo of vegetation in prescribed cropland areas in a global-climate model, and thereby estimate the near-term potential for bio-geoengineering to be a summertime cooling of more than 1°C throughout much of central North America and midlatitude Eurasia, equivalent to seasonally offsetting approximately one-fifth of regional warming due to doubling of atmospheric CO2. Ultimately, genetic modification of plant leaf waxes or canopy structure could achieve greater temperature reductions, although better characterization of existing intraspecies variability is needed first. [Copyright &y& Elsevier]
- Published
- 2009
- Full Text
- View/download PDF
36. An oceanic origin for the increase of atmospheric radiocarbon during the Younger Dryas.
- Author
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Singarayer, Joy S., Richards, David A., Ridgwell, Andy, Valdes, Paul J., Austin, William E. N., and Beck, J. Warren
- Published
- 2008
- Full Text
- View/download PDF
37. Antarctic last interglacial isotope peak in response to sea ice retreat not ice-sheet collapse.
- Author
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Holloway, Max D., Sime, Louise C., Singarayer, Joy S., Tindall, Julia C., Bunch, Pete, and Valdes, Paul J.
- Published
- 2016
- Full Text
- View/download PDF
38. Holocene variations in peatland methane cycling associated with the Asian summer monsoon system.
- Author
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Zheng, Yanhong, Singarayer, Joy S., Cheng, Peng, Yu, Xuefeng, Liu, Zhao, Valdes, Paul J., and Pancost, Richard D.
- Published
- 2014
- Full Text
- View/download PDF
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