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Author: Mary Kathleen Brennan Publisher: ISBN: Category : Languages : en Pages : 57
Book Description
Arctic sea ice concentrations have undergone rapid declines in recent decades. Many factors have been shown to contribute to this decline, and much of it has been attributed to greenhouse gas forcing and natural variability. In order to understand the relative roles of these factors on Arctic sea ice decline, a longer record of spatially complete data is needed. This project employs data assimilation to combine climate model output and proxy records to reconstruct past climate fields using the Last Millennium Reanalysis (LMR) framework, resulting in spatially complete gridded fields with annual resolution over the last two millennia. First the use of the LMR framework to reconstruct Arctic sea ice concentrations is tested through two methods: pseudo proxy experiments and comparing real proxy reconstructions to other records. Pseudo proxy results indicate strong performance in reconstructing Arctic sea ice. Correlation coefficients between the true and reconstructed values range between 0.63 and 0.77 depending on the climate model output used in the assimilation. The total Arctic sea ice extent reconstructed with the LMR using real proxy data compare well with satellite observations with correlation coefficients ranging between 0.54 and 0.84 depending on the climate model data used in the assimilation. These reconstructions were also compared to other records that precede satellite data and the LMR reconstructions show larger and longer lasting sea ice decline in response to early 20th century warming. The total sea ice extent minimum observed in these reconstructions between 1920-1960 is similar to the values observed in the 1990s. Next, two major questions are investigated using the 2000-year Arctic sea ice reconstruction: (1) Are the current sea ice changes unprecedented? and (2) Does sea ice respond to volcanic eruptions? The first is investigated through examining the distribution of total Arctic sea ice extent. The results indicate that both the trends and values of sea ice extent observed in the satellite era are unprecedented with respect to the LMR reconstruction of the last 1000 years. The second question is investigated through a composite average of sea ice extent before and after the 23 largest volcanic eruptions. These results show a statistically significant increase in total Arctic sea ice extent one year after an eruption. Finally, the sensitivity of these reconstructions to proxy location, model prior and the number of prior ensemble members used in the data assimilation scheme is examined. These experiments indicate that the proxies in the Arctic region (above 60N) explain most of the variance in the LMR sea ice reconstructions as expected. The role of the model prior is investigated by comparing the covariance between surface air temperature and Arctic sea ice across four different models. Overall the covariance is very similar except in some isolated regions in central Russia and China, in the North Atlantic and the central Pacific. In these regions the correlation coefficient is positive, but the coefficient of efficiency is negative indicating that there is a difference in the mean or variance in the covariance across models. 200 ensemble members are found to be sufficient in representing the variance in the full 1000 year last millennium model runs.
Author: Mary Kathleen Brennan Publisher: ISBN: Category : Languages : en Pages : 57
Book Description
Arctic sea ice concentrations have undergone rapid declines in recent decades. Many factors have been shown to contribute to this decline, and much of it has been attributed to greenhouse gas forcing and natural variability. In order to understand the relative roles of these factors on Arctic sea ice decline, a longer record of spatially complete data is needed. This project employs data assimilation to combine climate model output and proxy records to reconstruct past climate fields using the Last Millennium Reanalysis (LMR) framework, resulting in spatially complete gridded fields with annual resolution over the last two millennia. First the use of the LMR framework to reconstruct Arctic sea ice concentrations is tested through two methods: pseudo proxy experiments and comparing real proxy reconstructions to other records. Pseudo proxy results indicate strong performance in reconstructing Arctic sea ice. Correlation coefficients between the true and reconstructed values range between 0.63 and 0.77 depending on the climate model output used in the assimilation. The total Arctic sea ice extent reconstructed with the LMR using real proxy data compare well with satellite observations with correlation coefficients ranging between 0.54 and 0.84 depending on the climate model data used in the assimilation. These reconstructions were also compared to other records that precede satellite data and the LMR reconstructions show larger and longer lasting sea ice decline in response to early 20th century warming. The total sea ice extent minimum observed in these reconstructions between 1920-1960 is similar to the values observed in the 1990s. Next, two major questions are investigated using the 2000-year Arctic sea ice reconstruction: (1) Are the current sea ice changes unprecedented? and (2) Does sea ice respond to volcanic eruptions? The first is investigated through examining the distribution of total Arctic sea ice extent. The results indicate that both the trends and values of sea ice extent observed in the satellite era are unprecedented with respect to the LMR reconstruction of the last 1000 years. The second question is investigated through a composite average of sea ice extent before and after the 23 largest volcanic eruptions. These results show a statistically significant increase in total Arctic sea ice extent one year after an eruption. Finally, the sensitivity of these reconstructions to proxy location, model prior and the number of prior ensemble members used in the data assimilation scheme is examined. These experiments indicate that the proxies in the Arctic region (above 60N) explain most of the variance in the LMR sea ice reconstructions as expected. The role of the model prior is investigated by comparing the covariance between surface air temperature and Arctic sea ice across four different models. Overall the covariance is very similar except in some isolated regions in central Russia and China, in the North Atlantic and the central Pacific. In these regions the correlation coefficient is positive, but the coefficient of efficiency is negative indicating that there is a difference in the mean or variance in the covariance across models. 200 ensemble members are found to be sufficient in representing the variance in the full 1000 year last millennium model runs.
Author: Mary Kathleen Brennan Publisher: ISBN: Category : Languages : en Pages : 0
Book Description
Arctic sea ice has undergone rapid declines in recent decades. Given the short satellite record (1979–present), disentangling the relative role of natural variability and anthropogenic forcing on recent declines remains an important unresolved problem. In order to acquire a longer, reliable record of Arctic sea ice we employ data assimilation to combine temperature observations and climate model output. This technique results in fully gridded spatial fields of various climate variables throughout the Instrumental Era (1850-present). Specifically, the goal of this research is to reconstruct Arctic sea ice coverage and thickness on both annual and monthly timescales. We first reconstruct Arctic sea ice on annual timescales using an offline approach where each time step is independent from one another. This work reveals larger declines in total Arctic sea ice extent during the early 20th century (1900–1940) than previously estimated. Next, we build a Linear Inverse Model to forecast Arctic sea ice and other climate conditions on monthly timescales. We find that the Linear Inverse Model is able to skillfully forecast Arctic climate conditions during statistically stable time periods and is thus most useful when used as a model emulator. We then embed the Linear Inverse Model into a data assimilation scheme to produce monthly reconstructions of Arctic climate throughout the Instrumental Era.
Author: Thomas Johannes Maierhofer Publisher: ISBN: Category : Languages : en Pages : 0
Book Description
The short satellite-observed period from 1979 to 2023 has seen the Antarctic sea ice changedramatically. The sea ice generally increased until 2014 then precipitously decreased from 2014 to 2017. Record lows were then observed in February 2022 and February 2023. To evaluate these recent changes in the context of anthropogenic climate change requires information on Antarctic sea ice variability over the full 20th century. However, only temporally and spatially sparse data are available before 1979, creating a need for statistical reconstructions. We create a stochastic ensemble reconstruction of monthly Antarctic sea ice extent from 1900-1979 using a novel Bayesian spatio-temporal model. This model produces a set of 2500 plausible reconstructions of sea ice extent by sector. These reconstructions improve on prior approaches with realistic month-to-month changes and interdecadal trends as well as plausible interactions between the sectors. These unique features allow the direct computation of extreme event probabilities for the pre-satellite period of the 20th century. For example, we compute a 0.44% probability of reconstructing a decline in total Antarctic sea ice extent as extreme or more extreme than the 2014-2017 decline. We compute a 16% probability of observing a sea ice minimum as low or lower than the February 2022 minimum in total sea ice extent of 2.22 mio. km2, and a probability of 4% for the February 2023 minimum of 2.04 mio. km2. We also propose a novel approach to modeling the Antarctic sea ice edge using a functional regression model. The sea ice edge on a given day is treated as a continuous set of points circling the South Pole and the latitudes of these points are modeled as a function of their longitude. This enables the estimation and visualization of a circumpolar annual cycle and interannual development of the sea ice, providing novel insight into the regionality of sea ice variability. We develop statistical techniques for reconstructing 1966-1978 Antarctic sea ice extent using early satellite images in the visible and infrared spectrum. These images have not previously been analyzed due to severe missingness and cloud cover occluding the sea ice. Combining extensive preprocessing with modern statistical methods, we produce monthly sea ice concentration maps from which we compute historic sea ice extent.
Author: David N. Thomas Publisher: John Wiley & Sons ISBN: 0470756926 Category : Technology & Engineering Languages : en Pages : 419
Book Description
Sea ice, which covers up to 7% of the planet’s surface, is a major component of the world’s oceans, partly driving ocean circulation and global climate patterns. It provides a habitat for a rich diversity of marine organisms, and is an extremely valuable source of information in studies of global climate change and the evolution of present day life forms. Increasingly sea ice is being used as a proxy for extraterrestrial ice covered systems. Sea Ice provides a comprehensive review of our current available knowledge of polar pack ice, the study of which is severely constrained by the logistic difficulties of working in such harsh and remote regions of the earth. The book’s editors, Drs Thomas and Dieckmann have drawn together an impressive group of international contributing authors, providing a well-edited and integrated volume, which will stand for many years as the standard work on the subject. Contents of the book include details of the growth, microstructure and properties of sea ice, large-scale variations in thickness and characteristics, its primary production, micro-and macrobiology, sea ice as a habitat for birds and mammals, sea ice biogeochemistry, particulate flux, and the distribution and significance of palaeo sea ice. Sea Ice is an essential purchase for oceanographers and marine scientists, environmental scientists, biologists, geochemists and geologists. All those involved in the study of global climate change will find this book to contain a wealth of important information. All libraries in universities and research establishments where these subjects are studied and taught will need multiple copies on their shelves. David Thomas is at the School of Ocean Sciences, University of Wales, Bangor, UK. Gerhard Dieckmann is at the Alfred Wegener Institute for Polar and Marine Research, Bremerhaven, Germany
Author: Intergovernmental Panel on Climate Change (IPCC) Publisher: Cambridge University Press ISBN: 1139917196 Category : Science Languages : en Pages : 1554
Book Description
This Fifth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC) will again form the standard scientific reference for all those concerned with climate change and its consequences, including students and researchers in environmental science, meteorology, climatology, biology, ecology and atmospheric chemistry. It provides invaluable material for decision makers and stakeholders at international, national and local level, in government, businesses, and NGOs. This volume provides: • An authoritative and unbiased overview of the physical science basis of climate change • A more extensive assessment of changes observed throughout the climate system than ever before • New dedicated chapters on sea-level change, biogeochemical cycles, clouds and aerosols, and regional climate phenomena • Extensive coverage of model projections, both near-term and long-term climate projections • A detailed assessment of climate change observations, modelling, and attribution for every continent • A new comprehensive atlas of global and regional climate projections for 35 regions of the world
Author: Eustathios Chiotis Publisher: CRC Press ISBN: 1351260235 Category : Science Languages : en Pages : 406
Book Description
This book highlights climate as a complex physical, chemical, biological, and geological system, in perpetual change, under astronomical, predominantly, solar control. It has been shaped to some degree through the past glaciation cycles repeated in the last three million years. The Holocene, the current interglacial epoch which started ca. 11,700 years ago, marks the transition from the Stone Age to the unprecedented cultural evolution of our civilization. Significant climate changes have been recorded in natural archives during the Holocene, including the rapid waning of ice sheets, millennial shifting of the monsoonal fringe in the northern hemisphere, and abrupt centennial events. A typical case of severe environmental change is the greening of Sahara in the Early Holocene and the gradual desertification again since the fifth millennium before present. Climate Changes in the Holocene: Impact, Adaptation, and Resilience investigates the impact of natural climate changes on humans and civilization through case studies from various places, periods, and climates. Earth and human society are approached as a complex system, thereby emphasizing the necessity to improve adaptive capacity in view of the anthropogenic global warming and ecosystem degradation. Features: Written by distinguished experts, the book presents the fundamentals of the climate system, the unparalleled progress achieved in the last decade in the fields of intensified research for improved understanding of the carbon cycle, climate components, and their interaction. Presents the application of paleoclimatology and modeling in climate reconstruction. Examines the new era of satellite-based climate monitoring and the prospects of reduced carbon dioxide emissions.
Author: Intergouvernemental panel on climate change. Working group 1 Publisher: Cambridge University Press ISBN: 110705799X Category : Climatic changes Languages : en Pages : 1553
Book Description
The report also provides a comprehensive assessment of past and future sea level change in a dedicated chapter.
Author: Mary Kathleen Brennan
Author: Mary Kathleen Brennan
Author: Mary Kathleen Brennan
Author: Thomas Johannes Maierhofer
Author: Dabang Jiang
Author: Adam Philip
Author: Xiaotong Xiao
Author: David N. Thomas
Author: Intergovernmental Panel on Climate Change (IPCC)
Author: Eustathios Chiotis
Author: Intergouvernemental panel on climate change. Working group 1