Author
Udya Kuwar Thapa
Other affiliations: Hodges University
Bio: Udya Kuwar Thapa is an academic researcher from University of Minnesota. The author has contributed to research in topics: Sea surface temperature & Global temperature. The author has an hindex of 3, co-authored 3 publications receiving 259 citations. Previous affiliations of Udya Kuwar Thapa include Hodges University.
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University of Southern California1, Northern Arizona University2, MathWorks3, University of Arizona4, Australian National University5, United States Geological Survey6, Australian Antarctic Division7, University of Tasmania8, University of Maryland, College Park9, University of Melbourne10, University of Cambridge11, Spanish National Research Council12, University of Wollongong13, University of Bern14, Ca' Foscari University of Venice15, University of Texas at Austin16, University of Bergen17, Chinese Academy of Sciences18, Norwegian Polar Institute19, National University of Cuyo20, University of Washington21, University of Adelaide22, Victoria University of Wellington23, Swiss Federal Institute for Forest, Snow and Landscape Research24, University of Montpellier25, National Taiwan Ocean University26, Columbia University27, Louisiana State University28, University of Maine29, Arctic and Antarctic Research Institute30, Saint Petersburg State University31, Northumbria University32, Lund University33, Institut national de la recherche scientifique34, Tribhuvan University35, Nepal Academy of Science and Technology36, University of Ottawa37, Université catholique de Louvain38, Hirosaki University39, University of Gothenburg40, Xiamen University41, National Institute of Polar Research42, Japan Agency for Marine-Earth Science and Technology43, Aix-Marseille University44, National Institute of Water and Atmospheric Research45, Russian Academy of Sciences46, Autonomous University of Barcelona47, British Antarctic Survey48, University of Tübingen49, University of the Witwatersrand50, University of Brighton51, Alfred Wegener Institute for Polar and Marine Research52, Université Paris-Saclay53, Sukachev Institute of Forest54, University of Toronto55, University at Buffalo56, Australian Nuclear Science and Technology Organisation57, Aarhus University58, University of Florence59, Pierre-and-Marie-Curie University60, Paul Scherrer Institute61, University of Minnesota62, Concordia University63, University of Regina64, National Centre for Antarctic and Ocean Research65, University of New South Wales66, University of the Ryukyus67, National Oceanic and Atmospheric Administration68, University of Colorado Boulder69, Lehigh University70, Australian Institute of Marine Science71, Free University of Berlin72
TL;DR: A community-sourced database of temperature-sensitive proxy records from the PAGES2k initiative, suited to investigations of global and regional temperature variability over the Common Era, and is shared in the Linked Paleo Data (LiPD) format, including serializations in Matlab, R and Python.
Abstract: Reproducible climate reconstructions of the Common Era (1 CE to present) are key to placing industrial-era warming into the context of natural climatic variability. Here we present a community-sourced database of temperature-sensitive proxy records from the PAGES2k initiative. The database gathers 692 records from 648 locations, including all continental regions and major ocean basins. The records are from trees, ice, sediment, corals, speleothems, documentary evidence, and other archives. They range in length from 50 to 2000 years, with a median of 547 years, while temporal resolution ranges from biweekly to centennial. Nearly half of the proxy time series are significantly correlated with HadCRUT4.2 surface temperature over the period 1850–2014. Global temperature composites show a remarkable degree of coherence between high- and low-resolution archives, with broadly similar patterns across archive types, terrestrial versus marine locations, and screening criteria. The database is suited to investigations of global and regional temperature variability over the Common Era, and is shared in the Linked Paleo Data (LiPD) format, including serializations in Matlab, R and Python.
260 citations
TL;DR: In this article, a tree-ring width chronology was developed from Picea smithiana (Wall.) Boiss in Khaptad National Park, which is located in the far-western Nepalese Himalaya.
Abstract: We developed a new, 422-year long tree-ring width chronology (spanning AD 1591–2012) from Picea smithiana (Wall.) Boiss in Khaptad National Park, which is located in the far-western Nepalese Himalaya. Seasonal correlation analysis revealed significant indirect relationship with spring temperature and lead to the reconstruction of March–May average temperature for the past 373 years (AD 1640–2012). The reconstruction was found significant based on validation statistics commonly used in tree-ring based climate reconstruction. Furthermore, it was validated through spatial correlation with gridded temperature data. This temperature reconstruction identified several periods of warming and cooling. The reconstruction did not show the significant pattern of cooling during the Little Ice Age but there were few cold episodes recorded. The spring temperature revealed relationship with different Sea Surface Temperature index over the equatorial Pacific Ocean, which showed linkages with climatic variability in a global scale.
49 citations
TL;DR: In this paper, the authors developed a set of tree-ring width records for Abies spectablis (D.Don Spach) in the Manang valley of central Nepal Himalaya and tested how tree growth and the relationship between tree growth, and climate varied across a 450m elevation transect.
37 citations
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TL;DR: No evidence for preindustrial globally coherent cold and warm epochs is found, indicating that preindustrial forcing was not sufficient to produce globally synchronous extreme temperatures at multidecadal and centennial timescales, and provides strong evidence that anthropogenic global warming is not only unparalleled in terms of absolute temperatures, but also unprecedented in spatial consistency within the context of the past 2,000 years.
Abstract: Earth’s climate history is often understood by breaking it down into constituent climatic epochs1. Over the Common Era (the past 2,000 years) these epochs, such as the Little Ice Age2–4, have been characterized as having occurred at the same time across extensive spatial scales5. Although the rapid global warming seen in observations over the past 150 years does show nearly global coherence6, the spatiotemporal coherence of climate epochs earlier in the Common Era has yet to be robustly tested. Here we use global palaeoclimate reconstructions for the past 2,000 years, and find no evidence for preindustrial globally coherent cold and warm epochs. In particular, we find that the coldest epoch of the last millennium—the putative Little Ice Age—is most likely to have experienced the coldest temperatures during the fifteenth century in the central and eastern Pacific Ocean, during the seventeenth century in northwestern Europe and southeastern North America, and during the mid-nineteenth century over most of the remaining regions. Furthermore, the spatial coherence that does exist over the preindustrial Common Era is consistent with the spatial coherence of stochastic climatic variability. This lack of spatiotemporal coherence indicates that preindustrial forcing was not sufficient to produce globally synchronous extreme temperatures at multidecadal and centennial timescales. By contrast, we find that the warmest period of the past two millennia occurred during the twentieth century for more than 98 per cent of the globe. This provides strong evidence that anthropogenic global warming is not only unparalleled in terms of absolute temperatures5, but also unprecedented in spatial consistency within the context of the past 2,000 years.
248 citations
Oeschger Centre for Climate Change Research1, University of Costa Rica2, Northern Arizona University3, Chinese Academy of Sciences4, University of Southern California5, University of Maryland, College Park6, University of Edinburgh7, British Antarctic Survey8, University of Washington9, University of Melbourne10, Stockholm University11
TL;DR: Reconstructions and simulations qualitatively agree on the amplitude of the unforced global mean multidecadal temperature variability, thereby increasing confidence in future projections of climate change on these timescales.
Abstract: Multi-decadal surface temperature changes may be forced by natural as well as anthropogenic factors, or arise unforced from the climate system. Distinguishing these factors is essential for estimating sensitivity to multiple climatic forcings and the amplitude of the unforced variability. Here we present 2,000-year-long global mean temperature reconstructions using seven different statistical methods that draw from a global collection of temperature-sensitive paleoclimate records. Our reconstructions display synchronous multi-decadal temperature fluctuations, which are coherent with one another and with fully forced CMIP5 millennial model simulations across the Common Era. The most significant attribution of pre-industrial (1300-1800 CE) variability at multi-decadal timescales is to volcanic aerosol forcing. Reconstructions and simulations qualitatively agree on the amplitude of the unforced global mean multi-decadal temperature variability, thereby increasing confidence in future projections of climate change on these timescales. The largest warming trends at timescales of 20 years and longer occur during the second half of the 20th century, highlighting the unusual character of the warming in recent decades.
221 citations
TL;DR: Five different statistical methods were applied to reconstruct the GMST of the past 12,000 years (Holocene) and the results were aggregated to generate a multi-method ensemble of plausible GMST and latitudinal-zone temperature reconstructions with a realistic range of uncertainties.
Abstract: An extensive new multi-proxy database of paleo-temperature time series (Temperature 12k) enables a more robust analysis of global mean surface temperature (GMST) and associated uncertainties than was previously available. We applied five different statistical methods to reconstruct the GMST of the past 12,000 years (Holocene). Each method used different approaches to averaging the globally distributed time series and to characterizing various sources of uncertainty, including proxy temperature, chronology and methodological choices. The results were aggregated to generate a multi-method ensemble of plausible GMST and latitudinal-zone temperature reconstructions with a realistic range of uncertainties. The warmest 200-year-long interval took place around 6500 years ago when GMST was 0.7 °C (0.3, 1.8) warmer than the 19th Century (median, 5th, 95th percentiles). Following the Holocene global thermal maximum, GMST cooled at an average rate −0.08 °C per 1000 years (−0.24, −0.05). The multi-method ensembles and the code used to generate them highlight the utility of the Temperature 12k database, and they are now available for future use by studies aimed at understanding Holocene evolution of the Earth system.
176 citations
Oeschger Centre for Climate Change Research1, University of Bern2, University of New South Wales3, Oregon State University4, Australian National University5, University of Cambridge6, Max Planck Society7, British Antarctic Survey8, University of Copenhagen9, University of Bordeaux10, Lamont–Doherty Earth Observatory11, University of Bremen12, University of Toronto13, Durham University14, Leibniz Center for Tropical Marine Ecology15, Alfred Wegener Institute for Polar and Marine Research16, University of Geneva17, Ca' Foscari University of Venice18, Siberian Federal University19, GNS Science20, Queen's University21, University of Lausanne22, Université du Québec à Montréal23, University of Southern California24, University of Nebraska–Lincoln25, University of Bristol26, Adam Mickiewicz University in Poznań27, Yale University28, Université Paris-Saclay29, National Center for Atmospheric Research30, Bjerknes Centre for Climate Research31, École pratique des hautes études32, United States Global Change Research Program33, University of Kiel34, Lund University35, Chinese Academy of Sciences36, Northeast Normal University37, Lehigh University38, ETH Zurich39, Utrecht University40, Peking University41
TL;DR: In this article, an observation-based synthesis of the understanding of past intervals with temperatures within the range of projected future warming suggests that there is a low risk of runaway greenhouse gas feedbacks for global warming of no more than 2 °C.
Abstract: Over the past 3.5 million years, there have been several intervals when climate conditions were warmer than during the pre-industrial Holocene. Although past intervals of warming were forced differently than future anthropogenic change, such periods can provide insights into potential future climate impacts and ecosystem feedbacks, especially over centennial-to-millennial timescales that are often not covered by climate model simulations. Our observation-based synthesis of the understanding of past intervals with temperatures within the range of projected future warming suggests that there is a low risk of runaway greenhouse gas feedbacks for global warming of no more than 2 °C. However, substantial regional environmental impacts can occur. A global average warming of 1–2 °C with strong polar amplification has, in the past, been accompanied by significant shifts in climate zones and the spatial distribution of land and ocean ecosystems. Sustained warming at this level has also led to substantial reductions of the Greenland and Antarctic ice sheets, with sea-level increases of at least several metres on millennial timescales. Comparison of palaeo observations with climate model results suggests that, due to the lack of certain feedback processes, model-based climate projections may underestimate long-term warming in response to future radiative forcing by as much as a factor of two, and thus may also underestimate centennial-to-millennial-scale sea-level rise.
160 citations
TL;DR: It is shown that a weaker latitudinal temperature gradient—that is, warming of the Arctic with respect to the Equator—during the early to middle part of the Holocene coincided with substantial decreases in mid-latitude net precipitation, consistent with the hypothesis that a weakened temperature gradient led to weaker mid-Latitude westerly flow, weaker cyclones and decreased net terrestrial mid- latitude precipitation.
Abstract: The latitudinal temperature gradient between the Equator and the poles influences atmospheric stability, the strength of the jet stream and extratropical cyclones1–3. Recent global warming is weakening the annual surface gradient in the Northern Hemisphere by preferentially warming the high latitudes4; however, the implications of these changes for mid-latitude climate remain uncertain5,6. Here we show that a weaker latitudinal temperature gradient—that is, warming of the Arctic with respect to the Equator—during the early to middle part of the Holocene coincided with substantial decreases in mid-latitude net precipitation (precipitation minus evapotranspiration, at 30° N to 50° N). We quantify the evolution of the gradient and of mid-latitude moisture both in a new compilation of Holocene palaeoclimate records spanning from 10° S to 90° N and in an ensemble of mid-Holocene climate model simulations. The observed pattern is consistent with the hypothesis that a weaker temperature gradient led to weaker mid-latitude westerly flow, weaker cyclones and decreased net terrestrial mid-latitude precipitation. Currently, the northern high latitudes are warming at rates nearly double the global average4, decreasing the Equator-to-pole temperature gradient to values comparable with those in the early to middle Holocene. If the patterns observed during the Holocene hold for current anthropogenically forced warming, the weaker latitudinal temperature gradient will lead to considerable reductions in mid-latitude water resources. A reduced gradient in temperatures between low and high latitudes during the Holocene led to drier mid-latitudes.
155 citations