186 research outputs found
Climate of the Last Glacial Maximum: sensitivity studies and modelâdata comparison with the LOVECLIM coupled model.
The Last Glacial Maximum climate is one of the classical benchmarks used both to test the ability of coupled models to simulate climates different from that of the present-day and to better understand the possible range of mechanisms that could be involved in future climate change. It also bears the advantage of being one of the most well documented periods with respect to palaeoclimatic records, allowing a thorough data-model comparison. We present here an ensemble of Last Glacial Maximum climate simulations obtained with the Earth System model LOVECLIM, including coupled dynamic atmosphere, ocean and vegetation components. The climate obtained using standard parameter values is then compared to available proxy data for the surface ocean, vegetation, oceanic circulation and atmospheric conditions. Interestingly, the oceanic circulation obtained resembles that of the present-day, but with increased overturning rates. As this result is in contradiction with the current palaeoceanographic view, we ran a range of sensitivity experiments to explore the response of the model and the possibilities for other oceanic circulation states. After a critical review of our LGM state with respect to available proxy data, we conclude that the oceanic circulation obtained is not inconsistent with ocean circulation proxy data, although the water characteristics (temperature, salinity) are not in full agreement with water mass proxy data. The consistency of the simulated state is further reinforced by the fact that the mean surface climate obtained is shown to be generally in agreement with the most recent reconstructions of vegetation and sea surface temperatures, even at regional scales
An Atlantic-Pacific ventilation seesaw across the last deglaciation
It has been proposed that the rapid rise of atmospheric CO2across the last deglaciation was driven by the release of carbon from an extremely radiocarbon-depleted abyssal ocean reservoir that was âventedâ to the atmosphere primarily via the deep-and intermediate overturning loops in the Southern Ocean. While some radiocarbon observations from the intermediate ocean appear to confirm this hypothesis, others appear to refute it. Here we use radiocarbon measurements in paired benthic-and planktonic foraminifera to reconstruct the benthicâplanktonic14C age offset (i.e. âventilation ageâ) of intermediate waters in the western equatorial Atlantic. Our results show clear increases in local radiocarbon-based ventilation ages during Heinrich-Stadial 1 (HS1) and the Younger Dryas (YD). These are found to coincide with opposite changes of similar magnitude observed in the Pacific, demonstrating a âseesawâ in the ventilation of the intermediate Atlantic and Pacific Oceans that numerical model simulations of North Atlantic overturning collapse indicate was primarily driven by North Pacific overturning. We propose that this AtlanticâPacific ventilation seesaw would have combined with a previously identified North AtlanticâSouthern Ocean ventilation seesaw to enhance oceanâatmosphere CO2exchange during a âcollapseâ of the North Atlantic deep overturning limb. Whereas previous work has emphasized a more passive role for intermediate waters in deglacial climate change (merely conveying changes originating in the Southern Ocean) we suggest instead that the intermediate water seesaw played a more active role via relatively subtle but globally coordinated changes in ocean dynamics that may have further influenced oceanâatmosphere carbon exchange.We are grateful to Adam Scrivner for technical assistance in the laboratory, as well as the Royal Society and NERC grant NE/L006421/1 for research support. The UVic ESCM numerical ex-periments were performed on a computational cluster from the NCI National Facility systems at the Australian National University through the National Computational Merit Allocation Scheme sup-ported by the Australian Government. A.T. and T.F. acknowledge support from the US NSF grants 1341311, 1400914. L.M. is sup-ported by the Australian Research Council grant DE150100107.This is the final version. It was first published by Elsevier at http://www.sciencedirect.com/science/article/pii/S0012821X15003301
An AtlanticâPacific ventilation seesaw across the last deglaciation
It has been proposed that the rapid rise of atmospheric CO2 across the last deglaciation was driven by the release of carbon from an extremely radiocarbon-depleted abyssal ocean reservoir that was âventedâ to the atmosphere primarily via the deep- and intermediate overturning loops in the Southern Ocean. While some radiocarbon observations from the intermediate ocean appear to confirm this hypothesis, others appear to refute it. Here we use radiocarbon measurements in paired benthic- and planktonic foraminifera to reconstruct the benthicâplanktonic 14C age offset (i.e. âventilation ageâ) of intermediate waters in the western equatorial Atlantic. Our results show clear increases in local radiocarbon-based ventilation ages during Heinrich-Stadial 1 (HS1) and the Younger Dryas (YD). These are found to coincide with opposite changes of similar magnitude observed in the Pacific, demonstrating a âseesawâ in the ventilation of the intermediate Atlantic and Pacific Oceans that numerical model simulations of North Atlantic overturning collapse indicate was primarily driven by North Pacific overturning. We propose that this AtlanticâPacific ventilation seesaw would have combined with a previously identified North AtlanticâSouthern Ocean ventilation seesaw to enhance oceanâatmosphere CO2 exchange during a âcollapseâ of the North Atlantic deep overturning limb. Whereas previous work has emphasized a more passive role for intermediate waters in deglacial climate change (merely conveying changes originating in the Southern Ocean) we suggest instead that the intermediate water seesaw played a more active role via relatively subtle but globally coordinated changes in ocean dynamics that may have further influenced oceanâatmosphere carbon exchange
U.S. GLOBAL CHANGE RESEARCH PROGRAM CLIMATE SCIENCE SPECIAL REPORT (CSSR)
Fifth-Order Draft
Table of Contents
Front Matter
About This Report........................................................................................ 1
Guide to the Report......................................................................................4
Executive Summary ................................................................................... 12
Chapters
1. Our Globally Changing Climate .......................................................... 38
2. Physical Drivers of Climate Change ................................................... 98
3. Detection and Attribution of Climate Change .................................... 160
4. Climate Models, Scenarios, and Projections .................................... 186
5. Large-Scale Circulation and Climate Variability ................................ 228
6. Temperature Changes in the United States ...................................... 267
7. Precipitation Change in the United States ......................................... 301
8. Droughts, Floods, and Hydrology ......................................................... 336
9. Extreme Storms ....................................................................................... 375
10. Changes in Land Cover and Terrestrial Biogeochemistry ............ 405
11. Arctic Changes and their Effects on Alaska and the Rest of the United States..... 443
12. Sea Level Rise ....................................................................................... 493
13. Ocean Acidification and Other Ocean Changes .............................. 540
14. Perspectives on Climate Change Mitigation .................................... 584
15. Potential Surprises: Compound Extremes and Tipping Elements .......... 608
Appendices
A. Observational Datasets Used in Climate Studies ............................. 636
B. Weighting Strategy for the Fourth National Climate Assessment ................ 642
C. Detection and Attribution Methodologies Overview ............................ 652
D. Acronyms and Units ................................................................................. 664
E. Glossary ...................................................................................................... 66
U.S. GLOBAL CHANGE RESEARCH PROGRAM CLIMATE SCIENCE SPECIAL REPORT (CSSR)
Fifth-Order Draft
Table of Contents
Front Matter
About This Report........................................................................................ 1
Guide to the Report......................................................................................4
Executive Summary ................................................................................... 12
Chapters
1. Our Globally Changing Climate .......................................................... 38
2. Physical Drivers of Climate Change ................................................... 98
3. Detection and Attribution of Climate Change .................................... 160
4. Climate Models, Scenarios, and Projections .................................... 186
5. Large-Scale Circulation and Climate Variability ................................ 228
6. Temperature Changes in the United States ...................................... 267
7. Precipitation Change in the United States ......................................... 301
8. Droughts, Floods, and Hydrology ......................................................... 336
9. Extreme Storms ....................................................................................... 375
10. Changes in Land Cover and Terrestrial Biogeochemistry ............ 405
11. Arctic Changes and their Effects on Alaska and the Rest of the United States..... 443
12. Sea Level Rise ....................................................................................... 493
13. Ocean Acidification and Other Ocean Changes .............................. 540
14. Perspectives on Climate Change Mitigation .................................... 584
15. Potential Surprises: Compound Extremes and Tipping Elements .......... 608
Appendices
A. Observational Datasets Used in Climate Studies ............................. 636
B. Weighting Strategy for the Fourth National Climate Assessment ................ 642
C. Detection and Attribution Methodologies Overview ............................ 652
D. Acronyms and Units ................................................................................. 664
E. Glossary ...................................................................................................... 66
SMART: Spatial Modeling Algorithms for Reaction and Transport
Recent advances in microscopy and 3D reconstruction methods have allowed for
characterization of cellular morphology in unprecedented detail, including the
irregular geometries of intracellular subcompartments such as membrane-bound
organelles. These geometries are now compatible with predictive modeling of
cellular function. Biological cells respond to stimuli through sequences of
chemical reactions generally referred to as cell signaling pathways. The
propagation and reaction of chemical substances in cell signaling pathways can
be represented by coupled nonlinear systems of reaction-transport equations.
These reaction pathways include numerous chemical species that react across
boundaries or interfaces (e.g., the cell membrane and membranes of organelles
within the cell) and domains (e.g., the bulk cell volume and the interior of
organelles). Such systems of multi-dimensional partial differential equations
(PDEs) are notoriously difficult to solve because of their high dimensionality,
non-linearities, strong coupling, stiffness, and potential instabilities. In
this work, we describe Spatial Modeling Algorithms for Reactions and Transport
(SMART), a high-performance finite-element-based simulation package for model
specification and numerical simulation of spatially-varying reaction-transport
processes. SMART is based on the FEniCS finite element library, provides a
symbolic representation framework for specifying reaction pathways, and
supports geometries in 2D and 3D including large and irregular cell geometries
obtained from modern ultrastructural characterization methods.Comment: 5 pages, 2 figures, submitted to the Journal of Open Source Software
(JOSS), code available at https://github.com/RangamaniLabUCSD/smar
The intersection of diversity, equity, and inclusion with pediatric Patient and Family Advisory Councils
Patient and family advisory councils (PFACs) advance patient- and family-centered care within childrenâs hospitals but may not reflect the diversity of the communities they serve. We sought to assess PFAC diversity among childrenâs hospitals and explore barriers, drivers, and enablers of recruitment, retention, and engagement of patient and family advisors (PFAs) with diverse perspectives and backgrounds. We performed a mixed methods study to evaluate structure, composition, recruitment, and engagement strategies of childrenâs hospital PFACs. Individuals likely to have knowledge of or responsibility for PFACs at each Childrenâs Hospital Association (CHA) member hospital were asked to complete an electronic questionnaire. A subset of respondents from hospitals varying in size and region participated in 1-hour virtual interviews. We received valid responses from 166 (73%) of 228 CHA member hospitals. Eighty-eight percent reported having at least one PFAC. Only 21% selected âdefinitely trueâ when asked if their PFACs reflected the racial and ethnic diversity of the community served. Twelve respondents from various childrenâs hospitals participated in qualitative interviews. Five themes emerged: 1) Importance of Diversity in PFAC Membership; 2) Targeted, Personalized Recruitment and Engagement Strategies Facilitate Diverse PFACs; 3) Importance of Supporting PFAs from Diverse Backgrounds; 4) Ample Opportunities to Engage PFAs in Institutional Diversity, Equity, and Inclusion Efforts; and 5) External Factors as Drivers for Change within PFACs. Many PFACs are working to increase diversity, equity, and inclusion, but opportunities to close gaps remain. Findings may inform strategies to promote diversity, equity, and inclusion within PFACs across hospital systems.
Experience Framework
This article is associated with the Patient, Family & Community Engagement lens of The Beryl Institute Experience Framework (https://www.theberylinstitute.org/ExperienceFramework). Access other PXJ articles related to this lens. Access other resources related to this lens
The Growth and Decay of the Late Weichselian Ice Sheet in Western Svalbard and Adjacent Areas Based on Provenance Studies of Marine Sediments
The history of the Late Weichselian northwestern Barents Shelf, including western Svalbard, has been investigated by provenance/sedimentologist studies of five cores from the continental shelf and slope west of Svalbard. The chronostratigraphy of the cores is based on AMS 14C dates and oxygen isotope analyses. Interpretations of the cores suggest that the ice sheets of western Svalbard and northwestern Barents Sea experienced advances and retreats in two steps. The first significant ice advance beyond the present coastline occurred ca. 22,000 14C yr B.P. and was followed by an ice advance to the shelf edge ca. 18,000 14C yr B.P. Ice recession from the outer shelf and the southwestern Barents Sea began 14,800 14C yr B.P. and was followed by a second ice recession between 13,000 and 12,000 14 C yr B.P. during which ice withdrew from the inner shelf. A minor readvance of the ice sheet on the shelf west of Svalbard occurred close to 12,400 14C yr B.P. The first deglaciation event was associated with release of icebergs containing ice-rafted detritus, while the later episode also included significant amounts of meltwater and fine-grained sediment
Poor glycated haemoglobin control and adverse pregnancy outcomes in type 1 and type 2 diabetes mellitus: Systematic review of observational studies
BACKGROUND: Glycaemic control in women with diabetes is critical to satisfactory pregnancy outcome. A systematic review of two randomised trials concluded that there was no clear evidence of benefit from very tight versus tight glycaemic control for pregnant women with diabetes. METHODS: A systematic review of observational studies addressing miscarriage, congenital malformations and perinatal mortality among pregnant women with type 1 and type 2 diabetes was carried out. Literature searches were performed in MEDLINE, EMBASE, CINAHL and Cochrane Library. Observational studies with data on glycated haemoglobin (HbA(1c)) levels categorised into poor and optimal control (as defined by the study investigators) were selected. Relative risks and odds ratios were calculated for HbA(1c )and pregnancy outcomes. Adjusted relative risk estimates per 1-percent decrease in HbA(1c )were calculated for studies which contained information on mean and standard deviations of HbA(1c). RESULTS: The review identified thirteen studies which compared poor versus optimal glycaemic control in relation to maternal, fetal and neonatal outcomes. Twelve of these studies reported the outcome of congenital malformations and showed an increased risk with poor glycaemic control, pooled odds ratio 3.44 (95%CI, 2.30 to 5.15). For four of the twelve studies, it was also possible to calculate a relative risk reduction of congenital malformation for each 1-percent decrease in HbA(1c), these varied from 0.39 to 0.59. The risk of miscarriage was reported in four studies and was associated with poor glycaemic control, pooled odds ratio 3.23 (95%CI, 1.64 to 6.36). Increased perinatal mortality was also associated with poor glycaemic control, pooled odds ratio 3.03 (95%CI, 1.87 to 4.92) from four studies. CONCLUSION: This analysis quantifies the increase in adverse pregnancy outcomes in women with diabetes who have poor glycaemic control. Relating percentage risk reduction in HbA(1c )to relative risk of adverse pregnancy events may be useful in motivating women to achieve optimal control prior to conception
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