Paul J Valdes

Paul J Valdes
University of Bristol | UB · School of Geographical Sciences

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506
Publications
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24,151
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Publications

Publications (506)
Article
Full-text available
The ‘Greening’ and subsequent desertification of the Sahara during the early to mid-Holocene is a dramatic example of natural climate change. We analyse a suite of simulations with a newly palaeo-conditioned configuration of the HadCM3 coupled model that is able to capture an abrupt desertification of North Africa during this time. We find that thi...
Poster
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Ecological niche modelling is applied broadly in ecology to model a species’ niche and map suitable habitat. The approach links species’ occurrences with environmental predictors to statistically derive response curves. Although commonly applied to study extant taxa, ecological niche modelling is an emerging method in palaeobiology, providing oppor...
Article
Full-text available
Spinescence is an important functional trait possessed by many plant species for physical defence against mammalian herbivores. The development of spinescence must have been closely associated with both biotic and abiotic factors in the geological past, but knowledge of spinescence evolution suffers from a dearth of fossil records, with most studie...
Article
Full-text available
The growth of the Qinghai-Tibetan Plateau (QTP) during the Cenozoic drove dramatic climate and environmental change in this region. However, there has been limited comprehensive research into evolution of climate during this interval. Here we present a quantitative reconstruction using Bioclimatic Analysis (BA) and Joint Probability Density Functio...
Article
Full-text available
Quaternary Caspian Sea level variations depended on geophysical processes (affecting the opening and closing of gateways and basin size/shape) and hydro-climatological processes (affecting water balance). Disentangling the drivers of past Caspian Sea level variation, as well as the mechanisms by which they impacted the Caspian Sea level variation,...
Data
Supplementary information for "What are the drivers of Caspian Sea level variation during the late Quaternary?"
Data
Supplementary information for "What are the drivers of Caspian Sea level variation during the late Quaternary?"
Preprint
Paleoclimatic records provide valuable information about Holocene climate, revealing aspects of climate variability for a multitude of sites around the world. However, such data also possess limitations. Proxy networks are spatially uneven, seasonally biased, uncertain in time, and present a variety of challenges when used in concert to illustrate...
Article
Full-text available
Long transient simulations of the last deglaciation are increasingly being performed to identify the drivers of multiple rapid Earth system changes that occurred in this period. Such simulations frequently prescribe temporal variations in ice sheet properties, which can play an important role in controlling atmospheric and surface climate. To prese...
Article
Full-text available
Reconstructing the Paleogene topography and climate of central Tibet informs understanding of collisional tectonic mechanisms and their links to climate and biodiversity. Radiometric dates of volcanic/sedimentary rocks and paleotemperatures based on clumped isotopes within ancient soil carbonate nodules from the Lunpola Basin, part of an east-west...
Article
Full-text available
While paleoclimate records show that the Earth System is characterized by several different tipping points, their representation within Earth System models (ESMs) remains poorly constrained. This is because historical observations do not encompass variations large enough to provoke such regime changes, and paleoclimate conditions are rarely used to...
Preprint
Full-text available
During the late Eocene to the early Oligocene, marine records document a globally congruent record of declining carbon dioxide concentrations, Antarctic icesheet growth, and associated reorganisation of the global climate system. In contrast, the few existing terrestrial records demonstrate high heterogeneity of environmental change and are difficu...
Article
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The greenhouse-to-icehouse climate transition from the Eocene into the Oligocene is well documented by sea surface temperature records from the southwest Pacific and Antarctic margin, which show evidence of pronounced long-term cooling. However, identification of a driving mechanism depends on a better understanding of whether this cooling was also...
Article
Amidst long-term fluctuations of the abiotic environment, the degree to which life organizes into distinct biogeographic provinces (provinciality) can reveal the fundamental drivers of global biodiversity. Our understanding of present-day biogeography implies that changes in the distribution of continents across climatic zones have predictable effe...
Article
Full-text available
Benthic oxygen isotope records are commonly used as a proxy for global mean surface temperatures during the Late Cretaceous and Cenozoic, and the resulting estimates have been extensively used in characterizing major trends and transitions in the climate system and for analysing past climate sensitivity. However, some fundamental assumptions govern...
Article
Full-text available
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...
Preprint
Full-text available
The driver mechanisms of Dansgaard-Oeschger (DO) events remain uncertain, in part because many climate models do not show similar oscillatory behaviour. Here we present results from glacial simulations of the HadCM3B coupled atmosphere-ocean-vegetation model that show stochastic, quasi-periodical DO-scale variability. This variability is driven by...
Article
Full-text available
Factorisation (also known as “factor separation”) is widely used in the analysis of numerical simulations. It allows changes in properties of a system to be attributed to changes in multiple variables associated with that system. There are many possible factorisation methods; here we discuss three previously proposed factorisations that have been a...
Article
Full-text available
The Last Glacial Maximum (LGM, ∼ 21 000 years ago) has been a major focus for evaluating how well state-of-the-art climate models simulate climate changes as large as those expected in the future using paleoclimate reconstructions. A new generation of climate models has been used to generate LGM simulations as part of the Paleoclimate Modelling Int...
Article
During the early to mid-Holocene vegetation expanded to cover much of the present-day Sahara. Although driven by a well-understood difference in the orbital configuration, general circulation models have generally failed to simulate the required rainfall increase. One possible explanation is the presence of systematic biases in the representations...
Article
Today, Northeastern India receives some of the highest annual rainfall totals globally. The major portion of annual precipitation in this region falls during the Indian Summer Monsoon season (June–September); however, this region also receives a significant amount of rainfall during the pre-monsoon season (March–May). Here, we quantitatively recons...
Article
Full-text available
The growth of the Tibetan Plateau throughout the past 66 million years has profoundly affected the Asian climate, but how this unparalleled orogenesis might have driven vegetation and plant diversity changes in eastern Asia is poorly understood. We approach this question by integrating modeling results and fossil data. We show that growth of north...
Article
Full-text available
We present results from an ensemble of eight climate models, each of which has carried out simulations of the early Eocene climate optimum (EECO, ∼ 50 million years ago). These simulations have been carried out in the framework of the Deep-Time Model Intercomparison Project (DeepMIP; http://www.deepmip.org, last access: 10 January 2021); thus, all...
Article
Full-text available
Changes in the Greenland ice sheet (GIS) affect global sea level. Greenland stable water isotope (δ18O) records from ice cores offer information on past changes in the surface of the GIS. Here, we use the isotope-enabled Hadley Centre Coupled Model version 3 (HadCM3) climate model to simulate a set of last interglacial (LIG) idealised GIS surface e...
Article
Full-text available
Tibet’s ancient topography and its role in climatic and biotic evo- lution remain speculative due to a paucity of quantitative surface- height measurements through time and space, and sparse fossil records. However, newly discovered fossils from a present eleva- tion of ∼4,850 m in central Tibet improve substantially our knowl- edge of the ancient...
Article
Full-text available
The Tibetan Plateau was built through a succession of Gondwanan terranes colliding with Asia during the Mesozoic. These accretions produced a complex Paleogene topography of several predominantly east-west trending mountain ranges separated by deep valleys. Despite this piecemeal assembly and resultant complex relief, Tibet has traditionally been t...
Article
Our understanding regarding the onset and development of the modern South Asia monsoon (SAM) is still incomplete due to its complex nature and differing views about its relationship with major orographic features such as the Himalaya and Tibetan Plateau. Climate data derived from some terrestrial and marine sediments from the Neogene suggests the o...
Article
Warm periods in Earth's history offer opportunities to understand the dynamics of the Earth system under conditions that are similar to those expected in the near future. The Middle Pliocene warm period (MPWP), from 3.3 to 3.0 My B.P, is the most recent time when atmospheric CO2 levels were as high as today. However, climate model simulations of th...
Article
Full-text available
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, Ha...
Article
Full-text available
Views differ on the uplift history of the SE Tibetan Plateau and causal geodynamic mechanisms, yet reliable age-constrained paleoaltimetry in this region could test growth models of the entire plateau. Here we apply carbonate clumped isotope thermometry to well-dated carbonate paleosols and marls in the Gonjo Basin, SE Tibet, to reveal the topograp...
Article
Full-text available
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. Met...
Preprint
Full-text available
Benthic oxygen isotope records are commonly used as a proxy for global mean surface temperatures during the late Cretaceous and Cenozoic, and the resulting estimates have been extensively used in characterising major trends and transitions in the climate system, and for analysing past climate sensitivity. However, some fundamental assumptions gover...
Preprint
Full-text available
Factorisation is widely used in the analysis of numerical simulations. It allows changes in properties of a system to be attributed to changes in multiple variables associated with that system. There are many possible factorisation methods; here we discuss three previously-proposed factorisations that have been applied in the field of climate model...
Article
Full-text available
The often-used phrase ‘the uplift of the Tibetan Plateau’ implies a flat-surfaced Tibet rose as a coherent entity, and that uplift was driven entirely by the collision and northward movement of India. Here, we argue that these are misconceptions derived in large part from simplistic geodynamic and climate modeling, as well as proxy misinterpretatio...
Article
Full-text available
Palsas and peat plateaus are climatically sensitive landforms in permafrost peatlands. Climate envelope models have previously related palsa/peat plateau distributions in Europe to modern climate, but similar bioclimatic modelling has not been attempted for North America. Recent climate change has rendered many palsas/peat plateaus in this region,...
Article
Full-text available
Plain language summary Despite the North Pacific's importance in the global climate system, changes in the circulation of this region since the last ice age are poorly understood. Today, the North Pacific Ocean has distinct properties north and south of ~40°N: To the south, the warm surface waters form a circulation cell that moves clockwise (the s...
Preprint
Full-text available
Abstract. Changes in the Greenland ice sheet (GIS) affect global sea level. Greenland stable water isotope (δ<sup>18</sup>O) records from ice cores offer information on past changes in the surface of the GIS. Here, we use the isotope-enabled HadCM3 climate model to simulate a set of Last Interglacial (LIG) idealised GIS surface elevation change sce...
Article
Full-text available
The global and regional climate changed dramatically with the expansion of the Antarctic Ice Sheet at the Eocene–Oligocene transition (EOT). These large-scale changes are generally linked to declining atmospheric pCO2 levels and/or changes in Southern Ocean gateways such as the Drake Passage around this time. To better understand the Southern Hemis...
Article
Full-text available
An amendment to this paper has been published and can be accessed via a link at the top of the paper.
Article
A fossil leaf assemblage from latest Neogene (Pliocene) sediments exposed in Jharkhand of Chotonagpur Plateau, eastern India, is subjected to a CLAMP (Climate Leaf Analysis Multivariate Program) analysis using a new high spatial resolution (~1 km2) WorldClim2 gridded climate data and PhysgAsia2 calibration. The CLAMP analysis of 80 different morpho...
Preprint
Full-text available
Abstract. We present results from an ensemble of seven climate models, each of which has carried out simulations of the early Eocene climate optimum (EECO, ~ 50 million years ago). These simulations have been carried out in the framework of DeepMIP ( www.deepmip.org ), and as such all models have been configured with identical paleogeographic and v...
Article
The hydroclimate over Asia has undergone important changes over the Holocene with spatially asynchronous trends. Proxy-based evidence shows that North Asia was markedly drier than today during the early Holocene, whereas East Asia, influenced by the monsoon system, was substantially wetter. Yet, the causes behind this contrast are only partly under...
Preprint
Full-text available
North Pacific atmospheric and oceanic circulations are key missing pieces in our understanding of the reorganisation of the global climate system since the Last Glacial Maximum (LGM). Here, using a basin-wide compilation of planktic foraminiferal oxygen isotopes, we show that the North Pacific subpolar gyre extended ~3° further south during the LGM...
Article
Full-text available
Plain Language Summary Regional climate models (RCM) are often thought to simulate climate more accurately. However, RCMs use data generated by a lower‐resolution global model that is inputted at the boundaries, which may introduce biases. Here, we use three versions of the same model, a low‐resolution general circulation model (GCM), a high‐resolu...
Article
Full-text available
We present a continuous land-based climate reconstruction dataset extending back 60 kyr from 0 BP (1950) at 0.5° resolution on a monthly timestep for 0°N to 90°N. It has been generated from 42 discrete snapshot simulations using the HadCM3B-M2.1 coupled general circulation model. We incorporate Dansgaard-Oeschger (DO) and Heinrich events to represe...
Preprint
Full-text available
Constraining ocean circulation and its temporal variability is crucial for understanding changes in surface climate and the carbon cycle. Radiocarbon (¹⁴C) is often used as a geochemical tracer of ocean circulation, but interpreting ∆¹⁴C in geological archives is complex. Isotope-enabled models enable us to directly compare simulated ∆¹⁴C values to...
Article
Full-text available
The latitudinal diversity gradient (LDG), where the number of species increases from the poles to the Equator, ranks among the broadest and most notable biodiversity patterns on Earth. The pattern of species-rich tropics relative to species-poor temperate areas has been recognized for well over a century, but the generative mechanisms are still deb...
Article
Full-text available
The East Asian monsoon plays an integral role in human society, yet its geological history and controlling processes are poorly understood. Using a general circulation model and geological data, we explore the drivers controlling the evolution of the monsoon system over the past 150 million years. In contrast to previous work, we find that the mons...
Article
Full-text available
Botsyun et al . (Research Articles, 1 March 2019, eaaq1436) have suggested that the Tibetan Plateau was low (substantially less than 3000 meters) during the Eocene, based on a comparison of oxygen isotope proxy data with isotope-enabled climate model simulations. However, we contend that their conclusions are flawed as the result of a number of fai...
Article
Full-text available
Global and regional climate changed dramatically with the expansion of the Antarctic Ice sheet at the Eocene-Oligocene Transition (EOT). These large-scale changes are generally linked to declining atmospheric pCO2 levels and/or changes in Southern Ocean gateways such as the Drake Passage around this time. To better understand the Southern Hemispher...
Article
Full-text available
The Atlantic Meridional Overturning Circulation (AMOC) is an important component of the climate system, however its sensitivity to the terrestrial biosphere has been largely overlooked. Here the HadCM3 coupled climate model is run for millennial timescales to investigate the feedbacks between vegetation and the AMOC at increasing CO2. The impact of...
Article
Investigation of Holocene climate variability remains challenging. This is largely due to chronological uncertainties and complexities associated with proxies and their relationship with climatic drivers. Pertinent questions still exist regarding the Holocene climate in Ireland, particularly in the early Holocene. We present a mean July air tempera...