342 results on '"LeGrande, Allegra N."'
Search Results
2. Comment on gmd-2023-237
- Author
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LeGrande, Allegra N., primary
- Published
- 2024
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- View/download PDF
3. Ice Melt, Sea Level Rise and Superstorms: Evidence from Paleoclimate Data, Climate Modeling, and Modern Observations that 2{\deg}C Global Warming is Dangerous
- Author
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Hansen, James, Sato, Makiko, Hearty, Paul, Ruedy, Reto, Kelley, Maxwell, Masson-Delmotte, Valerie, Russell, Gary, Tselioudis, George, Cao, Junji, Rignot, Eric, Velicogna, Isabella, Tormey, Blair, Donovan, Bailey, Kandiano, Evgeniya, von Schuckmann, Karina, Kharecha, Pushker, Legrande, Allegra N., Bauer, Michael, and Lo, Kwok-Wai
- Subjects
Physics - Atmospheric and Oceanic Physics - Abstract
We use numerical climate simulations, paleoclimate data, and modern observations to study the effect of growing ice melt from Antarctica and Greenland. Meltwater tends to stabilize the ocean column, inducing amplifying feedbacks that increase subsurface ocean warming and ice shelf melting. Cold meltwater and induced dynamical effects cause ocean surface cooling in the Southern Ocean and North Atlantic, thus increasing Earth's energy imbalance and heat flux into most of the global ocean's surface. Southern Ocean surface cooling, while lower latitudes are warming, increases precipitation on the Southern Ocean, increasing ocean stratification, slowing deepwater formation, and increasing ice sheet mass loss. These feedbacks make ice sheets in contact with the ocean vulnerable to accelerating disintegration. We hypothesize that ice mass loss from the most vulnerable ice, sufficient to raise sea level several meters, is better approximated as exponential than by a more linear response. Doubling times of 10, 20 or 40 years yield multi-meter sea level rise in about 50, 100 or 200 years. Recent ice melt doubling times are near the lower end of the 10-40 year range, but the record is too short to confirm the nature of the response. The feedbacks, including subsurface ocean warming, help explain paleoclimate data and point to a dominant Southern Ocean role in controlling atmospheric CO2, which in turn exercised tight control on global temperature and sea level. The millennial (500-2000 year) time scale of deep ocean ventilation affects the time scale for natural CO2 change and thus the time scale for paleo global climate, ice sheet, and sea level changes, but this paleo millennial time scale should not be misinterpreted as the time scale for ice sheet response to a rapid large human-made climate forcing., Comment: 78 pages, 58 figures; submitted to Atmos. Chem. Phys
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- 2016
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- View/download PDF
4. The DeepMIP contribution to PMIP4: experimental design for model simulations of the EECO, PETM, and pre-PETM (version 1.0)
- Author
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Lunt, Daniel J, Huber, Matthew, Anagnostou, Eleni, Baatsen, Michiel LJ, Caballero, Rodrigo, DeConto, Rob, Dijkstra, Henk A, Donnadieu, Yannick, Evans, David, Feng, Ran, Foster, Gavin L, Gasson, Ed, von der Heydt, Anna S, Hollis, Chris J, Inglis, Gordon N, Jones, Stephen M, Kiehl, Jeff, Turner, Sandy Kirtland, Korty, Robert L, Kozdon, Reinhardt, Krishnan, Srinath, Ladant, Jean-Baptiste, Langebroek, Petra, Lear, Caroline H, LeGrande, Allegra N, Littler, Kate, Markwick, Paul, Otto-Bliesner, Bette, Pearson, Paul, Poulsen, Christopher J, Salzmann, Ulrich, Shields, Christine, Snell, Kathryn, Staerz, Michael, Super, James, Tabor, Clay, Tierney, Jessica E, Tourte, Gregory JL, Tripati, Aradhna, Upchurch, Garland R, Wade, Bridget S, Wing, Scott L, Winguth, Arne ME, Wright, Nicky M, Zachos, James C, and Zeebe, Richard E
- Subjects
Earth Sciences - Abstract
Abstract. Past warm periods provide an opportunity to evaluate climate models under extreme forcing scenarios, in particular high ( > 800 ppmv) atmospheric CO2 concentrations. Although a post hoc intercomparison of Eocene ( ∼ 50 Ma) climate model simulations and geological data has been carried out previously, models of past high-CO2 periods have never been evaluated in a consistent framework. Here, we present an experimental design for climate model simulations of three warm periods within the early Eocene and the latest Paleocene (the EECO, PETM, and pre-PETM). Together with the CMIP6 pre-industrial control and abrupt 4 × CO2 simulations, and additional sensitivity studies, these form the first phase of DeepMIP – the Deep-time Model Intercomparison Project, itself a group within the wider Paleoclimate Modelling Intercomparison Project (PMIP). The experimental design specifies and provides guidance on boundary conditions associated with palaeogeography, greenhouse gases, astronomical configuration, solar constant, land surface processes, and aerosols. Initial conditions, simulation length, and output variables are also specified. Finally, we explain how the geological data sets, which will be used to evaluate the simulations, will be developed.
- Published
- 2017
5. Precipitation 17O‐Excess Altered During Tropical Convection: Evidence From Monsoon Cold Surges in Singapore.
- Author
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Zhang, Yilin, He, Shaoneng, Wee, Bernie, LeGrande, Allegra N., Wang, Jingyu, Goodkin, Nathalie, and Wang, Xianfeng
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OXYGEN isotopes ,ATMOSPHERIC circulation ,HYDROGEN isotopes ,MONSOONS ,RAINFALL ,HUMIDITY ,CONVECTION (Meteorology) - Abstract
Despite the recent recognition of 17O‐excess as a promising new tracer for hydrological processes, our knowledge of the control mechanisms underlying 17O‐excess in tropical regions remains limited. To understand how microphysical processes during tropical convection affect precipitation isotope ratios, particularly 17O‐excess, in Singapore, we collected precipitation samples at minute intervals from six rain events associated with cold surges during the Northeast Monsoon seasons and analyzed their triple oxygen isotopes. Our results show that precipitation δ18O decreases in the convective zones and then gradually increases in the stratiform zones, while d‐excess exhibits an inverse trend. This correlation between δ18O and d‐excess indicates that rain evaporation plays a crucial role in regulating precipitation isotopes. Moreover, the rain events with a higher upstream rainout amount have lower δ18O and higher 17O‐excess values, suggesting that precipitation δ18O and 17O‐excess likely reflect the integrated upstream convective activity. Microphysical processes associated with upstream convection, such as rain evaporation and vapor recycling, are potential mechanisms that increase 17O‐excess values along moisture transport pathways for a rain event, and hence, undermine the effectiveness of 17O‐excess as a tracer of moisture source humidity. Contrary to the negative correlation observed in monthly precipitation, there is generally a positive correlation between d‐excess and 17O‐excess at the event scale. However, this correlation weakens as convective rain intensifies, suggesting that stronger convection can attenuate the positive correlation between d‐excess and 17O‐excess. Therefore, it is crucial to consider how tropical convection alters 17O‐excess when utilizing this tracer to interpret atmospheric dynamics and hydrological processes. Plain Language Summary: Our study investigates the impact of tropical weather systems and cloud processes on rainwater isotopes in Singapore. Understanding the factors influencing rainwater isotopes is crucial for interpreting climate dynamics. We collected rain samples at minute intervals from six events associated with cold surges during the Northeast Monsoon season and analyzed their oxygen and hydrogen isotopes. Our findings revealed that rainwater isotopes undergo changes as they progress through different phases of these weather systems, mainly due to rain evaporation. Furthermore, we observed that the amount of upstream rain affects the isotopic composition of rainwater in Singapore, suggesting that rainwater isotopes mirror the overall activity of upstream weather systems. Additionally, we found that regionally organized, stronger convection can alter the correlation between different isotopic parameters. Our research emphasizes the importance of considering the modifying effect of tropical weather systems on rainwater isotopic composition when utilizing these tracers to interpret atmospheric and hydrological processes. This highlights the significance of high‐resolution monitoring work and emphasizes the role of microphysical processes in understanding modern climate change. Key Points: Rain evaporation plays a significant role in shaping tropical precipitation isotopesIntegrated upstream convection may increase 17O‐excess along moisture transport pathwaysRegional convection can attenuate the positive correlation between d‐excess and 17O‐excess [ABSTRACT FROM AUTHOR]
- Published
- 2024
- Full Text
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6. Ice melt, sea level rise and superstorms: evidence from paleoclimate data, climate modeling, and modern observations that 2 ∘C global warming could be dangerous
- Author
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Hansen, James, Sato, Makiko, Hearty, Paul, Ruedy, Reto, Kelley, Maxwell, Masson-Delmotte, Valerie, Russell, Gary, Tselioudis, George, Cao, Junji, Rignot, Eric, Velicogna, Isabella, Tormey, Blair, Donovan, Bailey, Kandiano, Evgeniya, von Schuckmann, Karina, Kharecha, Pushker, Legrande, Allegra N, Bauer, Michael, and Lo, Kwok-Wai
- Subjects
Earth Sciences ,Oceanography ,Physical Geography and Environmental Geoscience ,Geology ,Climate Action ,physics.ao-ph ,Astronomical and Space Sciences ,Atmospheric Sciences ,Meteorology & Atmospheric Sciences ,Atmospheric sciences ,Climate change science - Abstract
We use numerical climate simulations, paleoclimate data, and modern observations to study the effect of growing ice melt from Antarctica and Greenland. Meltwater tends to stabilize the ocean column, inducing amplifying feedbacks that increase subsurface ocean warming and ice shelf melting. Cold meltwater and induced dynamical effects cause ocean surface cooling in the Southern Ocean and North Atlantic, thus increasing Earth's energy imbalance and heat flux into most of the global ocean's surface. Southern Ocean surface cooling, while lower latitudes are warming, increases precipitation on the Southern Ocean, increasing ocean stratification, slowing deepwater formation, and increasing ice sheet mass loss. These feedbacks make ice sheets in contact with the ocean vulnerable to accelerating disintegration. We hypothesize that ice mass loss from the most vulnerable ice, sufficient to raise sea level several meters, is better approximated as exponential than by a more linear response. Doubling times of 10, 20 or 40 years yield multi-meter sea level rise in about 50, 100 or 200 years. Recent ice melt doubling times are near the lower end of the 10-40-year range, but the record is too short to confirm the nature of the response. The feedbacks, including subsurface ocean warming, help explain paleoclimate data and point to a dominant Southern Ocean role in controlling atmospheric CO2, which in turn exercised tight control on global temperature and sea level. The millennial (500-2000-year) timescale of deep-ocean ventilation affects the timescale for natural CO2 change and thus the timescale for paleo-global climate, ice sheet, and sea level changes, but this paleo-millennial timescale should not be misinterpreted as the timescale for ice sheet response to a rapid, large, human-made climate forcing. These climate feedbacks aid interpretation of events late in the prior interglacial, when sea level rose to +6-9 m with evidence of extreme storms while Earth was less than 1 °C warmer than today. Ice melt cooling of the North Atlantic and Southern oceans increases atmospheric temperature gradients, eddy kinetic energy and baroclinicity, thus driving more powerful storms. The modeling, paleoclimate evidence, and ongoing observations together imply that 2 °C global warming above the preindustrial level could be dangerous. Continued high fossil fuel emissions this century are predicted to yield (1) cooling of the Southern Ocean, especially in the Western Hemisphere; (2) slowing of the Southern Ocean overturning circulation, warming of the ice shelves, and growing ice sheet mass loss; (3) slowdown and eventual shutdown of the Atlantic overturning circulation with cooling of the North Atlantic region; (4) increasingly powerful storms; and (5) nonlinearly growing sea level rise, reaching several meters over a timescale of 50-150 years. These predictions, especially the cooling in the Southern Ocean and North Atlantic with markedly reduced warming or even cooling in Europe, differ fundamentally from existing climate change assessments. We discuss observations and modeling studies needed to refute or clarify these assertions.
- Published
- 2016
7. The Toba supervolcano eruption caused severe tropical stratospheric ozone depletion
- Author
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Osipov, Sergey, Stenchikov, Georgiy, Tsigaridis, Kostas, LeGrande, Allegra N., Bauer, Susanne E., Fnais, Mohammed, and Lelieveld, Jos
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- 2021
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8. Ice Melt, Sea Level Rise and Superstorms: Evidence from Paleoclimate Data, Climate Modeling, and Modern Observations Implies that 2°C Global Warming Above the Preindustrial Level Would Be Dangerous
- Author
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Hansen, James, primary, Sato, Makiko, primary, Hearty, Paul, primary, Ruedy, Reto, primary, Kelley, Maxwell, primary, Masson-Delmotte, Valerie, primary, Russell, Gary, primary, Tselioudis, George, primary, Cao, Junji, primary, Rignot, Eric, primary, Velicogna, Isabella, primary, Tormey, Blair, primary, Donovan, Bailey, primary, Kandiano, Evgeniya, primary, von Schuckmann, Karina, primary, Kharecha, Pushker, primary, Legrande, Allegra N, primary, Bauer, Michael, primary, and Lo, Kwok-Wai, primary
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- 2020
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9. The impact of ENSO and NAO initial conditions and anomalies on the modeled response to Pinatubo-sized volcanic forcing.
- Author
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Weierbach, Helen, LeGrande, Allegra N., and Tsigaridis, Kostas
- Subjects
VOLCANIC eruptions ,EL Nino ,POLAR vortex ,NORTH Atlantic oscillation ,SOUTHERN oscillation ,CLIMATE change - Abstract
Strong, strato-volcanic eruptions are a substantial, intermittent source of natural climate variability. Initial atmospheric and oceanic conditions, such as El Niño Southern Oscillation (ENSO) and the North Atlantic Oscillation (NAO), also naturally impact climate on interannual timescales. We examine how initial conditions of ENSO and NAO contribute to the evolution of climate in the period following a Pinatubo-type eruption using a large (81-member) ensemble of model simulations in GISS model E2.1-G. Simulations are initialized from sampled conditions of ENSO and NAO using the protocol of the coordinated CMIP6 Volcanic Model Intercomparison Project (VolMIP) – where aerosols are forced with respect to time, latitude, and height. We analyze paired anomalous variations (perturbed – control) to understand changes in global and regional climate responses under positive, negative, and neutral ENSO and NAO conditions. In particular, we find that for paired anomalies there is a high probability of strong (∼1.5 ∘ C) warming of northern Eurasia surface air temperature in the first winter after the volcanic eruption for negative NAO ensembles coincident with decreased lower stratospheric temperature at the poles, decreased geopotential height, and strengthening of the stratospheric polar vortex. Climate anomalies (relative to average conditions across the control period), however, show no mean warming and suggest that the strength of this response is impacted by conditions present in the selected period of the control run. Again using paired anomalies, we also observe that under both +ENSO and -ENSO ensembles sea surface temperature decreases in the first post-eruptive boreal winter coinciding with surface cooling from volcanic aerosols. Neutral ENSO ensembles, on the other hand, show variability in their response with no clear trend in post-eruptive warming or cooling. In general, paired anomalies from unperturbed simulations give insight into the evolution of the climate response to volcanic forcing; however, when compared with anomalies from climatological conditions, it is clear that paired anomalies are significantly affected by sampled initial conditions occurring at the time of the volcanic eruption. [ABSTRACT FROM AUTHOR]
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- 2023
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10. Supplementary material to "The Impact of Background ENSO and NAO Conditions and Anomalies on the Modeled Response to Pinatubo-Sized Volcanic Forcing"
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Weierbach, Helen, primary, LeGrande, Allegra N., additional, and Tsigaridis, Kostas, additional
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- 2023
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11. The Impact of Background ENSO and NAO Conditions and Anomalies on the Modeled Response to Pinatubo-Sized Volcanic Forcing
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Weierbach, Helen, primary, LeGrande, Allegra N., additional, and Tsigaridis, Kostas, additional
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- 2023
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12. Reduction in ENSO variability during the mid-Holocene: a multi-model perspective
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Tiwari, Shivangi, primary, Pausata, Francesco S. R., additional, LeGrande, Allegra N., additional, Griffiths, Michael L., additional, Beltrami, Hugo, additional, de Vernal, Anne, additional, Tabor, Clay R., additional, Litchmore, Daniel, additional, Chandan, Deepak, additional, and Peltier, W. Richard, additional
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- 2023
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13. Dansgaard-Oeschger events in climate models: review and baseline Marine Isotope Stage 3 (MIS3) protocol
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European Union Center (US), Robinson, Alexander J. [0000-0003-3519-5293], Malmierca-Vallet, Irene, Sime, Louise C., Abe-Ouchi, Ayako, Born, Andreas, Bouttes, Nathaelle, DItlevsen, Peter, Erb, Michael P., Feulner, Georg, Gowan, Evan J., Gregoire, Lauren, Guo, Chuncheng, Harrison, Sandy P., Andres, Heather, Kageyama, Masa, Klockmann, Marlene, Lambert, Fabrice, LeGrande, Allegra N., Merkel, Ute, Nazarenko, Larissa S., Nisancioglu, Kerim H., Oliver, Kevin, Otto-Bliesner, Bette, Peltier, William R., Prange, Matthias, Rehfeld, Kira, Robinson, Alexander J., Tarasov, Lev, Valdes, Paul J., Vettoretti, Guido, Weitzel, Nils, Zhang, Qiong, Zhang, Xu, European Union Center (US), Robinson, Alexander J. [0000-0003-3519-5293], Malmierca-Vallet, Irene, Sime, Louise C., Abe-Ouchi, Ayako, Born, Andreas, Bouttes, Nathaelle, DItlevsen, Peter, Erb, Michael P., Feulner, Georg, Gowan, Evan J., Gregoire, Lauren, Guo, Chuncheng, Harrison, Sandy P., Andres, Heather, Kageyama, Masa, Klockmann, Marlene, Lambert, Fabrice, LeGrande, Allegra N., Merkel, Ute, Nazarenko, Larissa S., Nisancioglu, Kerim H., Oliver, Kevin, Otto-Bliesner, Bette, Peltier, William R., Prange, Matthias, Rehfeld, Kira, Robinson, Alexander J., Tarasov, Lev, Valdes, Paul J., Vettoretti, Guido, Weitzel, Nils, Zhang, Qiong, and Zhang, Xu
- Abstract
Dansgaard-Oeschger (D-O) events, millennial-scale climate oscillations between stadial and interstadial conditions (of up to 10-15°C in amplitude at high northern latitudes), occurred throughout the Marine Isotope Stage 3 (MIS3; 27.8-59.4ka) period. The climate modelling community up to now has not been able to answer the question of whether our climate models are too stable to simulate D-O events. To address this, this paper lays the ground-work for a MIS3 D-O protocol for general circulation models which are used in the International Panel for Climate Change (IPCC) assessments. We review the following: D-O terminology, community progress on simulating D-O events in these IPCC-class models (processes and published examples), and evidence about the boundary conditions under which D-O events occur. We find that no model exhibits D-O-like behaviour under pre-industrial conditions. Some, but not all, models exhibit D-O-like oscillations under MIS3 and/or full glacial conditions. Greenhouse gases and ice sheet configurations are crucial. However most models have not run simulations of long enough duration to be sure which models show D-O-like behaviour, under either MIS3 or full glacial states. We propose a MIS3 baseline protocol at 34ka, which features low obliquity values, medium to low MIS3 greenhouse gas values, and the intermediate ice sheet configuration, which our review suggests are most conducive to D-O-like behaviour in models. We also provide a protocol for a second freshwater (Heinrich-event-preconditioned) experiment, since previous work suggests that this variant may be helpful in preconditioning a state in models which is conducive to D-O events. This review provides modelling groups investigating MIS3 D-O oscillations with a common framework, which is aimed at (1) maximising the chance of the occurrence of D-O-like events in the simulations, (2) allowing more precise model-data evaluation, and (3) providing an adequate central point for modellers to expl
- Published
- 2023
14. Dansgaard-Oeschger events in climate models:review and baseline Marine Isotope Stage 3 (MIS3) protocol
- Author
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Malmierca-Vallet, Irene, Sime, Louise C., Abe-Ouchi, Ayako, Born, Andreas, Bouttes, Nathaelle, DItlevsen, Peter, Erb, Michael P., Feulner, Georg, Gowan, Evan J., Gregoire, Lauren, Guo, Chuncheng, Harrison, Sandy P., Andres, Heather, Kageyama, Masa, Klockmann, Marlene, Lambert, Fabrice, LeGrande, Allegra N., Merkel, Ute, Nazarenko, Larissa S., Nisancioglu, Kerim H., Oliver, Kevin, Otto-Bliesner, Bette, Peltier, William R., Prange, Matthias, Rehfeld, Kira, Robinson, Alexander J., Tarasov, Lev, Valdes, Paul J., Vettoretti, Guido, Weitzel, Nils, Zhang, Qiong, Zhang, Xu, Malmierca-Vallet, Irene, Sime, Louise C., Abe-Ouchi, Ayako, Born, Andreas, Bouttes, Nathaelle, DItlevsen, Peter, Erb, Michael P., Feulner, Georg, Gowan, Evan J., Gregoire, Lauren, Guo, Chuncheng, Harrison, Sandy P., Andres, Heather, Kageyama, Masa, Klockmann, Marlene, Lambert, Fabrice, LeGrande, Allegra N., Merkel, Ute, Nazarenko, Larissa S., Nisancioglu, Kerim H., Oliver, Kevin, Otto-Bliesner, Bette, Peltier, William R., Prange, Matthias, Rehfeld, Kira, Robinson, Alexander J., Tarasov, Lev, Valdes, Paul J., Vettoretti, Guido, Weitzel, Nils, Zhang, Qiong, and Zhang, Xu
- Abstract
Dansgaard-Oeschger (D-O) events, millennial-scale climate oscillations between stadial and interstadial conditions (of up to 10-15°C in amplitude at high northern latitudes), occurred throughout the Marine Isotope Stage 3 (MIS3; 27.8-59.4ka) period. The climate modelling community up to now has not been able to answer the question of whether our climate models are too stable to simulate D-O events. To address this, this paper lays the ground-work for a MIS3 D-O protocol for general circulation models which are used in the International Panel for Climate Change (IPCC) assessments. We review the following: D-O terminology, community progress on simulating D-O events in these IPCC-class models (processes and published examples), and evidence about the boundary conditions under which D-O events occur. We find that no model exhibits D-O-like behaviour under pre-industrial conditions. Some, but not all, models exhibit D-O-like oscillations under MIS3 and/or full glacial conditions. Greenhouse gases and ice sheet configurations are crucial. However most models have not run simulations of long enough duration to be sure which models show D-O-like behaviour, under either MIS3 or full glacial states. We propose a MIS3 baseline protocol at 34ka, which features low obliquity values, medium to low MIS3 greenhouse gas values, and the intermediate ice sheet configuration, which our review suggests are most conducive to D-O-like behaviour in models. We also provide a protocol for a second freshwater (Heinrich-event-preconditioned) experiment, since previous work suggests that this variant may be helpful in preconditioning a state in models which is conducive to D-O events. This review provides modelling groups investigating MIS3 D-O oscillations with a common framework, which is aimed at (1) maximising the chance of the occurrence of D-O-like events in the simulations, (2) allowing more precise model-data evaluation, and (3) providing an adequate central point for modellers to e
- Published
- 2023
15. Investigating hydroclimatic impacts of the 168–158 BCE volcanic quartet and their relevance to the Nile River basin and Egyptian history
- Author
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Singh, Ram, primary, Tsigaridis, Kostas, additional, LeGrande, Allegra N., additional, Ludlow, Francis, additional, and Manning, Joseph G., additional
- Published
- 2023
- Full Text
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16. On the remote impacts of mid-Holocene Saharan vegetation on South American hydroclimate: a modelling intercomparison
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Tiwari, Shivangi, primary, Ramos, Riovie D., additional, Pausata, Francesco S.R., additional, LeGrande, Allegra N., additional, Griffiths, Michael, additional, Beltrami, Hugo, additional, Wainer, ILana, additional, de Vernal, Anne, additional, Litchmore, Daniel T., additional, Chandan, Deepak, additional, Peltier, W Richard, additional, and Tabor, Clay R, additional
- Published
- 2022
- Full Text
- View/download PDF
17. A Double Bootstrap Approach to Superposed Epoch Analysis to Evaluate Response Uncertainty
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Rao, Mukund P, Cook, Edward R, Cook, Benjamin I, Anchukaitis, Kevin J, D'Arrigo, Rosanne D, Krusic, Paul J, and LeGrande, Allegra N
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Meteorology And Climatology - Abstract
The association between climate variability and episodic events, such as the antecedent moisture conditions prior to wildfire or the cooling following volcanic eruptions, is commonly assessed using Superposed Epoch Analysis (SEA). In SEA the epochal response is typically calculated as the average climate conditions prior to and following all event years or their deviation from climatology. However, the magnitude and significance of the inferred climate association may be sensitive to the selection or omission of individual key years, potentially resulting in a biased assessment of the relationship between these events and climate. Here we describe and test a modified double-bootstrap SEA that generates multiple unique draws of the key years and evaluates the sign, magnitude, and significance of event-climate relationships within a probabilistic framework. This multiple resampling helps quantify multiple uncertainties inherent in conventional applications of SEA within dendrochronology and paleoclimatology. We demonstrate our modified SEA by evaluating the volcanic cooling signal in a Northern Hemisphere tree-ring temperature reconstruction and the link between drought and wildfire events in the western United States. Finally, we make our Matlab and R code available to be adapted for future SEA applications.
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- 2019
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18. Clumped‐Isotope Constraint on Upper‐Tropospheric Cooling During the Last Glacial Maximum
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Banerjee, Asmita, primary, Yeung, Laurence Y., additional, Murray, Lee T., additional, Tie, Xin, additional, Tierney, Jessica E., additional, and Legrande, Allegra N., additional
- Published
- 2022
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19. The 8,200-Year BP Event
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LeGrande, Allegra N. and Gornitz, Vivien, editor
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- 2009
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20. Assessing the Impact of Large Volcanic Eruptions of the Last Millennium (850-1850 CE) on Australian Rainfall Regimes
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Blake, Stephanie A. P, Lewis, Sophie C, LeGrande, Allegra N, and Miller, Ron L
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Meteorology And Climatology - Abstract
Explosive volcanism is an important natural climate forcing, impacting global surface temperatures and regional precipitation. Although previous studies have investigated aspects of the impact of tropical volcanism on various ocean–atmosphere systems and regional climate regimes, volcanic eruptions remain a poorly understood climate forcing and climatic responses are not well constrained. In this study, volcanic eruptions are explored in particular reference to Australian precipitation, and both the Indian Ocean Dipole (IOD) and El Niño–Southern Oscillation (ENSO). Using nine realizations of the last millennium (LM) (850–1850CE) with different time-evolving forcing combinations, from the NASA GISS ModelE2-R, the impact of the six largest tropical volcanic eruptions of this period are investigated. Overall, we find that volcanic aerosol forcing increased the likelihood of El Niño and positive IOD conditions for up to four years following an eruption, and resulted in positive precipitation anomalies over north-west (NW) and south-east (SE) Australia. Larger atmospheric sulfate loading during larger volcanic eruptions coincided with more persistent positive IOD and El Niño conditions, enhanced positive precipitation anomalies over NW Australia, and dampened precipitation anomalies over SE Australia.
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- 2018
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21. Multi-model Comparison of the Volcanic Sulfate Deposition from the 1815 Eruption of Mt. Tambora
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Marshall, Lauren, Schmidt, Anja, Toohey, Matthew, Carslaw, Ken S, Mann, Graham W, Sigl, Michael, Khodri, Myriam, Timmreck, Claudia, Zanchettin, Davide, Ball, William T, Bekki, Slimane, Brooke, James S. A, Dhomse, Sandip, Johnson, Colin, Lamarque, Jean-Francois, LeGrande, Allegra N, Mills, Michael J, Niemeier, Ulrike, Pope, James O, Poulain, Virginie, Robock, Alan, Rozanov, Eugene, Stenke, Andrea, Sukhodolov, Timofei, Tilmes, Simone, Tsigaridis, Kostas, and Tummon, Fiona
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Geophysics - Abstract
The eruption of Mt. Tambora in 1815 was the largest volcanic eruption of the past 500 years. The eruption had significant climatic impacts, leading to the 1816 "year without a summer", and remains a valuable event from which to understand the climatic effects of large stratospheric volcanic sulfur dioxide injections. The eruption also resulted in one of the strongest and most easily identifiable volcanic sulfate signals in polar ice cores, which are widely used to reconstruct the timing and atmospheric sulfate loading of past eruptions. As part of the Model Intercomparison Project on the climatic response to Volcanic forcing (VolMIP), five state-of-the-art global aerosol models simulated this eruption. We analyze both simulated background (no Tambora) and volcanic (with Tambora) sulfate deposition to polar regions and compare to ice core records. The models simulate overall similar patterns of background sulfate deposition, although there are differences in regional details and magnitude. However, the volcanic sulfate deposition varies considerably between the models with differences in timing, spatial pattern and magnitude. Mean simulated deposited sulfate on Antarctica ranges from 19 to 264 kgkm-2 and on Greenland from 31 to 194 kgkm-2, as compared to the mean ice-core derived estimates of roughly 50 kgkm-2 for both Greenland and Antarctica. The ratio of the hemispheric atmospheric sulfate aerosol burden after the eruption to the average ice sheet deposited sulfate varies between models by up to a factor of 15. Sources of this inter-model variability include differences in both the formation and the transport of sulfate aerosol. Our results suggest that deriving relationships between sulfate deposited on ice sheets and atmospheric sulfate burdens from model simulations may be associated with greater uncertainties than previously thought.
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- 2018
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22. The PMIP4 Contribution to CMIP6-Part 4: Scientific Objectives and Experimental Design of the PMIP4-CMIP6 Last Glacial Maximum Experiments and PMIP4 Sensitivity Experiments
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Kageyama, Masa, Albani, Samuel, Braconnot, Pascale, Harrison, Sandy P, Hopcroft, Peter O, Ivanovic, Ruza F, Lambert, Fabrice, Marti, Olivier, Peltier, W. Richard, Peterschmitt, Jean-Yves, Roche, Didier M, Tarasov, Lev, Zhang, Xu, Brady, Esther C, Haywood, Alan M, LeGrande, Allegra N, Lunt, Daniel J, Mahowald, Natalie M, Mikolajewicz, Uwe, Nisancioglu, Kerim H, Otto-Bliesner, Bette L, Renssen, Hans, Tomas, Robert A, Zhang, Qiong, Abe-Ouchi, Ayako, Bartlein, Patrick J, Cao, Jian, Li, Qiang, Lohmann, Gerrit, Ohgaito, Rumi, Shi, Xiaoxu, Volodin, Evgeny, Yoshida, Kohei, Zhang, Xiao, and Zheng, Weipeng
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Meteorology And Climatology - Abstract
The Last Glacial Maximum (LGM, 21,000 years ago) is one of the suite of paleoclimate simulations included in the current phase of the Coupled Model Intercomparison Project (CMIP6). It is an interval when insolation was similar to the present, but global ice volume was at a maximum, eustatic sea level was at or close to a minimum, greenhouse gas concentrations were lower, atmospheric aerosol loadings were higher than today, and vegetation and land-surface characteristics were different from today. The LGM has been a focus for the Paleoclimate Modelling Intercomparison Project (PMIP) since its inception, and thus many of the problems that might be associated with simulating such a radically different climate are well documented. The LGM state provides an ideal case study for evaluating climate model performance because the changes in forcing and temperature between the LGM and pre-industrial are of the same order of magnitude as those projected for the end of the 21st century. Thus, the CMIP6 LGM experiment could provide additional information that can be used to constrain estimates of climate sensitivity. The design of the Tier 1 LGM experiment (lgm) includes an assessment of uncertainties in boundary conditions, in particular through the use of different reconstructions of the ice sheets and of the change in dust forcing. Additional (Tier 2) sensitivity experiments have been designed to quantify feedbacks associated with land-surface changes and aerosol loadings, and to isolate the role of individual forcings. Model analysis and evaluation will capitalize on the relative abundance of paleoenvironmental observations and quantitative climate reconstructions already available for the LGM.
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- 2017
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23. Investigating stable oxygen and carbon isotopic variability in speleothem records over the last millennium using multiple isotope-enabled climate models
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Bühler, Janica C., primary, Axelsson, Josefine, additional, Lechleitner, Franziska A., additional, Fohlmeister, Jens, additional, LeGrande, Allegra N., additional, Midhun, Madhavan, additional, Sjolte, Jesper, additional, Werner, Martin, additional, Yoshimura, Kei, additional, and Rehfeld, Kira, additional
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- 2022
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24. Future Climate Change Under SSP Emission Scenarios With GISS‐E2.1
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Nazarenko, Larissa S., primary, Tausnev, Nick, additional, Russell, Gary L., additional, Rind, David, additional, Miller, Ron L., additional, Schmidt, Gavin A., additional, Bauer, Susanne E., additional, Kelley, Maxwell, additional, Ruedy, Reto, additional, Ackerman, Andrew S., additional, Aleinov, Igor, additional, Bauer, Michael, additional, Bleck, Rainer, additional, Canuto, Vittorio, additional, Cesana, Grégory, additional, Cheng, Ye, additional, Clune, Thomas L., additional, Cook, Ben I., additional, Cruz, Carlos A., additional, Del Genio, Anthony D., additional, Elsaesser, Gregory S., additional, Faluvegi, Greg, additional, Kiang, Nancy Y., additional, Kim, Daehyun, additional, Lacis, Andrew A., additional, Leboissetier, Anthony, additional, LeGrande, Allegra N., additional, Lo, Ken K., additional, Marshall, John, additional, Matthews, Elaine E., additional, McDermid, Sonali, additional, Mezuman, Keren, additional, Murray, Lee T., additional, Oinas, Valdar, additional, Orbe, Clara, additional, García‐Pando, Carlos Pérez, additional, Perlwitz, Jan P., additional, Puma, Michael J., additional, Romanou, Anastasia, additional, Shindell, Drew T., additional, Sun, Shan, additional, Tsigaridis, Kostas, additional, Tselioudis, George, additional, Weng, Ensheng, additional, Wu, Jingbo, additional, and Yao, Mao‐Sung, additional
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- 2022
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25. Investigating stable oxygen and carbon isotopic variability in speleothem records over the last millennium using multiple isotope-enabled climate models
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Bühler, Janica C., Axelsson, Josefine, Lechleitner, Franziska A., Fohlmeister, Jens, LeGrande, Allegra N., Midhun, Madhavan, Sjolte, Jesper, Werner, Martin, Yoshimura, Kei, Rehfeld, Kira, Bühler, Janica C., Axelsson, Josefine, Lechleitner, Franziska A., Fohlmeister, Jens, LeGrande, Allegra N., Midhun, Madhavan, Sjolte, Jesper, Werner, Martin, Yoshimura, Kei, and Rehfeld, Kira
- Abstract
The incorporation of water isotopologues into the hydrology of general circulation models (GCMs) facilitates the comparison between modeled and measured proxy data in paleoclimate archives. However, the variability and drivers of measured and modeled water isotopologues, as well as the diversity of their representation in different models, are not well constrained. Improving our understanding of this variability in past and present climates will help to better constrain future climate change projections and decrease their range of uncertainty. Speleothems are a precisely datable terrestrial paleoclimate archives and provide well-preserved (semi-)continuous multivariate isotope time series in the lower latitudes and mid-latitudes and are therefore well suited to assess climate and isotope variability on decadal and longer timescales. However, the relationships of speleothem oxygen and carbon isotopes to climate variables are influenced by site-specific parameters, and their comparison to GCMs is not always straightforward. Here we compare speleothem oxygen and carbon isotopic signatures from the Speleothem Isotopes Synthesis and Analysis database version 2 (SISALv2) to the output of five different water-isotope-enabled GCMs (ECHAM5-wiso, GISS-E2-R, iCESM, iHadCM3, and isoGSM) over the last millennium (850–1850 CE). We systematically evaluate differences and commonalities between the standardized model simulation outputs. The goal is to distinguish climatic drivers of variability for modeled isotopes and compare them to those of measured isotopes. We find strong regional differences in the oxygen isotope signatures between models that can partly be attributed to differences in modeled surface temperature. At low latitudes, precipitation amount is the dominant driver for stable water isotope variability; however, at cave locations the agreement between modeled temperature variability is higher than for precipitation variability. While modeled isotopic signatures at cav
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- 2022
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26. Investigating stable oxygen and carbon isotopic variability in speleothem records over the last millennium using multiple isotope-enabled climate models
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Bühler, Janica C, Axelsson, Josefine, Lechleitner, Franziska A, Fohlmeister, Jens, LeGrande, Allegra N, Midhun, Madhavan, Sjolte, Jesper, Werner, Martin, Yoshimura, Kei, Rehfeld, Kira, Bühler, Janica C, Axelsson, Josefine, Lechleitner, Franziska A, Fohlmeister, Jens, LeGrande, Allegra N, Midhun, Madhavan, Sjolte, Jesper, Werner, Martin, Yoshimura, Kei, and Rehfeld, Kira
- Abstract
The incorporation of water isotopologues into the hydrology of general circulation models (GCMs) facilitates the comparison between modeled and measured proxy data in paleoclimate archives. However, the variability and drivers of measured and modeled water isotopologues, as well as the diversity of their representation in different models, are not well constrained. Improving our understanding of this variability in past and present climates will help to better constrain future climate change projections and decrease their range of uncertainty. Speleothems are a precisely datable terrestrial paleoclimate archives and provide well-preserved (semi-)continuous multivariate isotope time series in the lower latitudes and mid-latitudes and are therefore well suited to assess climate and isotope variability on decadal and longer timescales. However, the relationships of speleothem oxygen and carbon isotopes to climate variables are influenced by site-specific parameters, and their comparison to GCMs is not always straightforward. Here we compare speleothem oxygen and carbon isotopic signatures from the Speleothem Isotopes Synthesis and Analysis database version 2 (SISALv2) to the output of five different water-isotope-enabled GCMs (ECHAM5-wiso, GISSE2-R, iCESM, iHadCM3, and isoGSM) over the last millennium (850–1850 CE). We systematically evaluate differences and commonalities between the standardized model simulation outputs. The goal is to distinguish climatic drivers of variability for modeled isotopes and compare them to those of measured isotopes. We find strong regional differences in the oxygen isotope signatures between models that can partly be attributed to differences in modeled surface temperature. At low latitudes, precipitation amount is the dominant driver for stable water isotope variability; however, at cave locations the agreement between modeled temperature variability is higher than for precipitation variability. While modeled isotopic signatures at cave
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- 2022
27. The Impact of Background ENSO and NAO Conditions and Anomalies on the Modeled Response to Pinatubo-Sized Volcanic Forcing.
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Weierbach, Helen, LeGrande, Allegra N., and Tsigaridis, Kostas
- Abstract
Strong, strato-volcanic eruptions are a substantial, intermittent source of natural climate variability. Background atmospheric and oceanic conditions such as El Niño Southern Oscillation (ENSO) and the North Atlantic Oscillation (NAO) also naturally impact climate on regular time scales. We examine how background conditions of ENSO and NAO impact the climate's response to a Pinatubo-type eruption using a large (81-member) ensemble of model simulations in GISS Model E2.1-G. Simulations are sampled from possible background conditions under the protocol of the coordinated CMIP6 Volcanic Model Intercomparison Project (VolMIP) – where aerosol forcing with time, latitude, and height. We analyze paired paired anomalous variation (perturbed - control) to understand changes in global and regional climate responses under positive, negative, and neutral ENSO and NAO conditions. In particular, we find that for paired anomalies there is a high probability of strong (~1.5 °C) post-eruptive winter warming for negative NAO ensembles with analysis coincident with decreased lower stratospheric temperature at the poles, decreased geopotential height, and strengthening of the stratospheric polar vortex. Historical anomalies (relative to climatology) show no mean warming and suggest that strength of this response is impacted by control conditions. Again using paired anomalies, we also observe that positive and negative ENSO ensembles relax the ENSO anomaly in the first post-eruptive Boreal Winter while neutral-phase ensembles are variable and show no clear response. In general, paired anomalies give insight into the evolution of the climate response to volcanic forcing, but are significantly impacted by background climate conditions present in control conditions. [ABSTRACT FROM AUTHOR]
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- 2023
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28. Model performance in simulating the mid-Holocene Green Sahara
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Tiwari, Shivangi, primary, Ramos, Riovie, additional, Pausata, Francesco S. R., additional, LeGrande, Allegra N., additional, Griffiths, Michael L., additional, Beltrami, Hugo, additional, Chandan, Deepak, additional, de Vernal, Anne, additional, Litchmore, Daniel, additional, Peltier, Richard, additional, and Tabor, Clay R., additional
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- 2022
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29. Effects of forcing differences and initial conditions on inter-model agreement in the VolMIP volc-pinatubo-full experiment
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Zanchettin, Davide, primary, Timmreck, Claudia, additional, Khodri, Myriam, additional, Schmidt, Anja, additional, Toohey, Matthew, additional, Abe, Manabu, additional, Bekki, Slimane, additional, Cole, Jason, additional, Fang, Shih-Wei, additional, Feng, Wuhu, additional, Hegerl, Gabriele, additional, Johnson, Ben, additional, Lebas, Nicolas, additional, LeGrande, Allegra N., additional, Mann, Graham W., additional, Marshall, Lauren, additional, Rieger, Landon, additional, Robock, Alan, additional, Rubinetti, Sara, additional, Tsigaridis, Kostas, additional, and Weierbach, Helen, additional
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- 2022
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30. Investigating hydroclimatic impacts of the 168–158 BCE volcanic quartet and their relevance to the Nile River basin and Egyptian history
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Singh, Ram, primary, Tsigaridis, Kostas, additional, LeGrande, Allegra N., additional, Ludlow, Francis, additional, and Manning, Joseph G., additional
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- 2022
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31. Supplementary material to "Investigating hydroclimatic impacts of the 168–158 BCE volcanic quartet and their relevance to the Nile River basin and Egyptian history"
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Singh, Ram, primary, Tsigaridis, Kostas, additional, LeGrande, Allegra N., additional, Ludlow, Francis, additional, and Manning, Joseph G., additional
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- 2022
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32. How Did Climate and Humans Respond to Past Volcanic Eruptions?
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Toohey, Matthew, Ludlow, Francis, and Legrande, Allegra N
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Meteorology And Climatology - Abstract
To predict and prepare for future climate change, scientists are striving to understand how global-scale climatic change manifests itself on regional scales and also how societies adapt or don't to sometimes subtle and complex climatic changes. In this regard, the strongest volcanic eruptions of the past are powerful test cases, showcasing how the broad climate system responds to sudden changes in radiative forcing and how societies have responded to the resulting climatic shocks. These issues were at the heart of the inaugural workshop of the Volcanic Impacts on Climate and Society (VICS) Working Group, convened in June 2016 at the Lamont-Doherty Earth Observatory of Columbia University in Palisades, N.Y. The 3-day meeting gathered approximately 50 researchers, who presented work intertwining the history of volcanic eruptions and the physical processes that connect eruptions with human and natural systems on a global scale.
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- 2016
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33. Investigating oxygen and carbon isotopic relationships in speleothem records over the last millennium using multiple isotope-enabled climate models
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Bühler, Janica C., primary, Axelsson, Josefine M., additional, Lechleitner, Franziska A., additional, Fohlmeister, Jens, additional, LeGrande, Allegra N., additional, Midhun, Madhavan, additional, Sjolte, Jesper, additional, Werner, Martin, additional, Yoshimura, Kei, additional, and Rehfeld, Kira, additional
- Published
- 2021
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34. Supplementary material to "Investigating oxygen and carbon isotopic relationships in speleothem records over the last millennium using multiple isotope-enabled climate models"
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Bühler, Janica C., primary, Axelsson, Josefine M., additional, Lechleitner, Franziska A., additional, Fohlmeister, Jens, additional, LeGrande, Allegra N., additional, Midhun, Madhavan, additional, Sjolte, Jesper, additional, Werner, Martin, additional, Yoshimura, Kei, additional, and Rehfeld, Kira, additional
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- 2021
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35. Supplementary material to "Effects of forcing differences and initial conditions on inter-model agreement in the VolMIP volc-pinatubo-full experiment"
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Zanchettin, Davide, primary, Timmreck, Claudia, additional, Khodri, Myriam, additional, Schmidt, Anja, additional, Toohey, Matthew, additional, Abe, Manabu, additional, Bekki, Slimane, additional, Cole, Jason, additional, Fang, Shih-Wei, additional, Feng, Wuhu, additional, Hegerl, Gabriele, additional, Johnson, Ben, additional, Lebas, Nicolas, additional, LeGrande, Allegra N., additional, Mann, Graham W., additional, Marshall, Lauren, additional, Rieger, Landon, additional, Robock, Alan, additional, Rubinetti, Sara, additional, Tsigaridis, Kostas, additional, and Weierbach, Helen, additional
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- 2021
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36. Effects of forcing differences and initial conditions on inter-model agreement in the VolMIP volc-pinatubo-full experiment
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Zanchettin, Davide, primary, Timmreck, Claudia, additional, Khodri, Myriam, additional, Schmidt, Anja, additional, Toohey, Matthew, additional, Abe, Manabu, additional, Bekki, Slimane, additional, Cole, Jason, additional, Fang, Shih-Wei, additional, Feng, Wuhu, additional, Hegerl, Gabriele, additional, Johnson, Ben, additional, Lebas, Nicolas, additional, LeGrande, Allegra N., additional, Mann, Graham W., additional, Marshall, Lauren, additional, Rieger, Landon, additional, Robock, Alan, additional, Rubinetti, Sara, additional, Tsigaridis, Kostas, additional, and Weierbach, Helen, additional
- Published
- 2021
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37. Spring-summer temperatures since AD 1780 reconstructed from stable oxygen isotope ratios in white spruce tree-rings from the Mackenzie Delta, northwestern Canada
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Porter, Trevor J., Pisaric, Michael F. J., Field, Robert D., Kokelj, Steven V., Edwards, Thomas W. D., deMontigny, Peter, Healy, Richard, and LeGrande, Allegra N.
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- 2014
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38. Hemispherically Asymmetric Volcanic Forcing of Tropical Hydroclimate During the Last Millennium
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Colose, Christopher M, Legrande, Allegra N, and Vuille, Mathias
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Meteorology And Climatology - Abstract
Volcanic aerosols exert the most important natural radiative forcing of the last millennium. State-of-the-art paleoclimate simulations of this interval are typically forced with diverse spatial patterns of volcanic forcing, leading to different responses in tropical hydroclimate. Recently, theoretical considerations relating the intertropical convergence zone (ITCZ) position to the demands of global energy balance have emerged in the literature, allowing for a connection to be made between the paleoclimate simulations and recent developments in the understanding of ITCZ dynamics. These energetic considerations aid in explaining the well-known historical, paleoclimatic, and modeling evidence that the ITCZ migrates away from the hemisphere that is energetically deficient in response to asymmetric forcing. Here we use two separate general circulation model (GCM) suites of experiments for the last millennium to relate the ITCZ position to asymmetries in prescribed volcanic sulfate aerosols in the stratosphere and related asymmetric radiative forcing. We discuss the ITCZ shift in the context of atmospheric energetics and discuss the ramifications of transient ITCZ migrations for other sensitive indicators of changes in the tropical hydrologic cycle, including global streamflow. For the first time, we also offer insight into the large-scale fingerprint of water isotopologues in precipitation (delta sup 18 Op) in response to asymmetries in radiative forcing. The ITCZ shifts away from the hemisphere with greater volcanic forcing. Since the isotopic composition of precipitation in the ITCZ is relatively depleted compared to areas outside this zone, this meridional precipitation migration results in a large-scale enrichment (depletion) in the isotopic composition of tropical precipitation in regions the ITCZ moves away from (toward). Our results highlight the need for careful consideration of the spatial structure of volcanic forcing for interpreting volcanic signals in proxy records and therefore in evaluating the skill of Common Era climate model output.
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- 2016
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39. The Model Intercomparison Project on the Climatic Response to Volcanic Forcing (VolMIP): Experimental Design and Forcing Input Data for CMIP6
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Zanchettin, Davide, Khodri, Myriam, Timmreck, Claudia, Toohey, Matthew, Schmidt, Anja, Gerber, Edwin P, Hegerl, Gabriele, Robock, Alan, Pausata, Francesco, Ball, William T, Bauer, Susanne E, LeGrande, Allegra N, and Tsigaridis, Kostas
- Subjects
Meteorology And Climatology - Abstract
The enhancement of the stratospheric aerosol layer by volcanic eruptions induces a complex set of responses causing global and regional climate effects on a broad range of timescales. Uncertainties exist regarding the climatic response to strong volcanic forcing identified in coupled climate simulations that contributed to the fifth phase of the Coupled Model Intercomparison Project (CMIP5). In order to better understand the sources of these model diversities, the Model Intercomparison Project on the climatic response to Volcanic forcing (VolMIP) has defined a coordinated set of idealized volcanic perturbation experiments to be carried out in alignment with the CMIP6 protocol. VolMIP provides a common stratospheric aerosol data set for each experiment to minimize differences in the applied volcanic forcing. It defines a set of initial conditions to assess how internal climate variability contributes to determining the response. VolMIP will assess to what extent volcanically forced responses of the coupled ocean-atmosphere system are robustly simulated by state-of-the-art coupled climate models and identify the causes that limit robust simulated behavior, especially differences in the treatment of physical processes. This paper illustrates the design of the idealized volcanic perturbation experiments in the VolMIP protocol and describes the common aerosol forcing input data sets to be used.
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- 2016
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40. Role of Atmospheric Chemistry in the Climate Impacts of Stratospheric Volcanic Injections
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Legrande, Allegra N, Tsigaridis, Kostas, and Bauer, Susanne E
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Meteorology And Climatology - Abstract
The climate impact of a volcanic eruption is known to be dependent on the size, location and timing of the eruption. However, the chemistry and composition of the volcanic plume also control its impact on climate. It is not just sulfur dioxide gas, but also the coincident emissions of water, halogens and ash that influence the radiative and climate forcing of an eruption. Improvements in the capability of models to capture aerosol microphysics, and the inclusion of chemistry and aerosol microphysics modules in Earth system models, allow us to evaluate the interaction of composition and chemistry within volcanic plumes in a new way. These modeling efforts also illustrate the role of water vapor in controlling the chemical evolution, and hence climate impacts, of the plume. A growing realization of the importance of the chemical composition of volcanic plumes is leading to a more sophisticated and realistic representation of volcanic forcing in climate simulations, which in turn aids in reconciling simulations and proxy reconstructions of the climate impacts of past volcanic eruptions. More sophisticated simulations are expected to help, eventually, with predictions of the impact on the Earth system of any future large volcanic eruptions.
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- 2016
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41. Supplement of: The Influence of Volcanic Eruptions on the Climate of Tropical South America During the Last Millennium in an Isotope-Enabled General Circulation Model
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Colose, Christopher, LeGrande, Allegra N, and Vuille, Mathias
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Meteorology And Climatology - Abstract
Currently, little is known on how volcanic eruptions impact large-scale climate phenomena such as South American paleo-intertropical Convergence Zone (ITCZ) position and summer monsoon behavior. In this paper, an analysis of observations and model simulations is employed to assess the influence of large volcanic eruptions on the climate of tropical South America. This problem is first considered for historically recent volcanic episodes for which more observations are available but where fewer events exist and the confounding effects of El NioSouthern Oscillation (ENSO) lead to inconclusive interpretation of the impact of volcanic eruptions at the continental scale. Therefore, we also examine a greater number of reconstructed volcanic events for the period 850CE to present that are incorporated into the NASA GISS ModelE2-R simulation of the last millennium.An advantage of this model is its ability to explicitly track water isotopologues throughout the hydrologic cycle and simulating the isotopic imprint following a large eruption. This effectively removes a degree of uncertainty associated with error-prone conversion of isotopic signals into climate variables, and allows for a direct comparison between GISS simulations and paleoclimate proxy records.Our analysis reveals that both precipitation and oxygen isotope variability respond with a distinct seasonal and spatial structure across tropical South America following an eruption. During austral winter, the heavy oxygen isotope in precipitation is enriched, likely due to reduced moisture convergence in the ITCZ domain and reduced rainfall over northern South America. During austral summer, however, more negative values of the precipitation isotopic composition are simulated over Amazonia, despite reductions in rainfall, suggesting that the isotopic response is not a simple function of the amount effect. During the South American monsoon season, the amplitude of the temperature response to volcanic forcing is larger than the rather weak and spatially less coherent precipitation signal, complicating the isotopic response to changes in the hydrologic cycle.
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- 2016
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42. The Influence of Volcanic Eruptions on the Climate of Tropical South America During the Last Millennium in an Isotope-Enabled General Circulation Model
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Colose, Christopher M, LeGrande, Allegra N, and Vuille, Mathias
- Subjects
Meteorology And Climatology - Abstract
Currently, little is known on how volcanic eruptions impact large-scale climate phenomena such as South American paleo-intertropical Convergence Zone (ITCZ) position and summer monsoon behavior. In this paper, an analysis of observations and model simulations is employed to assess the influence of large volcanic eruptions on the climate of tropical South America. This problem is first considered for historically recent volcanic episodes for which more observations are available but where fewer events exist and the confounding effects of El Niño-Southern Oscillation (ENSO) lead to inconclusive interpretation of the impact of volcanic eruptions at the continental scale. Therefore, we also examine a greater number of reconstructed volcanic events for the period 850 CE to present that are incorporated into the NASA GISS ModelE2-R simulation of the last millennium. An advantage of this model is its ability to explicitly track water isotopologues throughout the hydrologic cycle and simulating the isotopic imprint following a large eruption. This effectively removes a degree of uncertainty associated with error-prone conversion of isotopic signals into climate variables, and allows for a direct comparison between GISS simulations and paleoclimate proxy records. Our analysis reveals that both precipitation and oxygen isotope variability respond with a distinct seasonal and spatial structure across tropical South America following an eruption. During austral winter, the heavy oxygen isotope in precipitation is enriched, likely due to reduced moisture convergence in the ITCZ domain and reduced rainfall over northern South America. During austral summer, however, more negative values of the precipitation isotopic composition are simulated over Amazonia, despite reductions in rainfall, suggesting that the isotopic response is not a simple function of the "amount effect". During the South American monsoon season, the amplitude of the temperature response to volcanic forcing is larger than the rather weak and spatially less coherent precipitation signal, complicating the isotopic response to changes in the hydrologic cycle.
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- 2016
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43. How Will Sea Ice Loss Affect the Greenland Ice Sheet? On the Puzzling Features of Greenland Ice-Core Isotopic Composition
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Pausata, Francesco S. R, Legrande, Allegra N, and Roberts, William H. G
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Meteorology And Climatology - Abstract
The modern cryosphere, Earth's frozen water regime, is in fast transition. Greenland ice cores show how fast theses changes can be, presenting evidence of up to 15 C warming events over timescales of less than a decade. These events, called Dansgaard/Oeschger (D/O) events, are believed to be associated with rapid changes in Arctic sea ice, although the underlying mechanisms are still unclear. The modern demise of Arctic sea ice may, in turn, instigate abrupt changes on the Greenland Ice Sheet. The Arctic Sea Ice and Greenland Ice Sheet Sensitivity (Ice2Ice Chttps://ice2ice.b.uib.noD) initiative, sponsored by the European Research Council, seeks to quantify these past rapid changes to improve our understanding of what the future may hold for the Arctic. Twenty scientists gathered in Copenhagen as part of this initiative to discuss the most recent observational, technological, and model developments toward quantifying the mechanisms behind past climate changes in Greenland. Much of the discussion focused on the causes behind the changes in stable water isotopes recorded in ice cores. The participants discussed sources of variability for stable water isotopes and framed ways that new studies could improve understanding of modern climate. The participants also discussed how climate models could provide insights into the relative roles of local and nonlocal processes in affecting stable water isotopes within the Greenland Ice Sheet. Presentations of modeling results showed how a change in the source or seasonality of precipitation could occur not only between glacial and modern climates but also between abrupt events. Recent fieldwork campaigns illustrate an important role of stable isotopes in atmospheric vapor and diffusion in the final stable isotope signal in ice. Further, indications from recent fieldwork campaigns illustrate an important role of stable isotopes in atmospheric vapor and diffusion in the final stable isotope signal in ice. This feature complicates the quantitative interpretation of ice core signals but also makes the stable ice isotope signal a more robust regional indicator of climate, speakers noted. Meeting participants agreed that to further our understanding of these relationships, we need more process-focused field and laboratory campaigns.
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- 2016
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44. Volcanic Eruptions and Climate
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LeGrande, Allegra N and Anchukaitis, Kevin J
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Meteorology And Climatology - Abstract
Volcanic eruptions represent some of the most climatically important and societally disruptive short-term events in human history. Large eruptions inject ash, dust, sulfurous gases (e.g. SO2, H2S), halogens (e.g. Hcl and Hbr), and water vapor into the Earth's atmosphere. Sulfurous emissions principally interact with the climate by converting into sulfate aerosols that reduce incoming solar radiation, warming the stratosphere and altering ozone creation, reducing global mean surface temperature, and suppressing the hydrological cycle. In this issue, we focus on the history, processes, and consequences of these large eruptions that inject enough material into the stratosphere to significantly affect the climate system. In terms of the changes wrought on the energy balance of the Earth System, these transient events can temporarily have a radiative forcing magnitude larger than the range of solar, greenhouse gas, and land use variability over the last millennium. In simulations as well as modern and paleoclimate observations, volcanic eruptions cause large inter-annual to decadal-scale changes in climate. Active debates persist concerning their role in longer-term (multi-decadal to centennial) modification of the Earth System, however.
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- 2015
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45. A data–model approach to interpreting speleothem oxygen isotope records from monsoon regions
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Parker, Sarah E., primary, Harrison, Sandy P., additional, Comas-Bru, Laia, additional, Kaushal, Nikita, additional, LeGrande, Allegra N., additional, and Werner, Martin, additional
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- 2021
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46. The PMIP4 Last Glacial Maximum experiments: preliminary results and comparison with the PMIP3 simulations
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Kageyama, Masa, primary, Harrison, Sandy P., additional, Kapsch, Marie-L., additional, Lofverstrom, Marcus, additional, Lora, Juan M., additional, Mikolajewicz, Uwe, additional, Sherriff-Tadano, Sam, additional, Vadsaria, Tristan, additional, Abe-Ouchi, Ayako, additional, Bouttes, Nathaelle, additional, Chandan, Deepak, additional, Gregoire, Lauren J., additional, Ivanovic, Ruza F., additional, Izumi, Kenji, additional, LeGrande, Allegra N., additional, Lhardy, Fanny, additional, Lohmann, Gerrit, additional, Morozova, Polina A., additional, Ohgaito, Rumi, additional, Paul, André, additional, Peltier, W. Richard, additional, Poulsen, Christopher J., additional, Quiquet, Aurélien, additional, Roche, Didier M., additional, Shi, Xiaoxu, additional, Tierney, Jessica E., additional, Valdes, Paul J., additional, Volodin, Evgeny, additional, and Zhu, Jiang, additional
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- 2021
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47. A multi-model CMIP6-PMIP4 study of Arctic sea ice at 127 ka: sea ice data compilation and model differences
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Kageyama, Masa, Sime, Louise C., Sicard, Marie, Guarino, Maria-Vittoria, de Vernal, Anne, Stein, Ruediger, Schroeder, David, Malmierca-Vallet, Irene, Abe-Ouchi, Ayako, Bitz, Cecilia, Braconnot, Pascale, Brady, Esther C., Cao, Jian, Chamberlain, Matthew A., Feltham, Danny, Guo, Chuncheng, LeGrande, Allegra N., Lohmann, Gerrit, Meissner, Katrin J., Menviel, Laurie, Morozova, Polina, Nisancioglu, Kerim H., Otto-Bliesner, Bette L., O'ishi, Ryouta, Ramos Buarque, Silvana, Salas y Melia, David, Sherriff-Tadano, Sam, Stroeve, Julienne, Shi, Xiaoxu, Sun, Bo, Tomas, Robert A., Volodin, Evgeny, Yeung, Nicholas K. H., Zhang, Qiong, Zhang, Zhongshi, Zheng, Weipeng, and Ziehn, Tilo
- Abstract
The Last Interglacial period (LIG) is a period with increased summer insolation at high northern latitudes, which results in strong changes in the terrestrial and marine cryosphere. Understanding the mechanisms for this response via climate modelling and comparing the models' representation of climate reconstructions is one of the objectives set up by the Paleoclimate Modelling Intercomparison Project for its contribution to the sixth phase of the Coupled Model Intercomparison Project. Here we analyse the results from 16 climate models in terms of Arctic sea ice. The multi-model mean reduction in minimum sea ice area from the pre industrial period (PI) to the LIG reaches 50 % (multi-model mean LIG area is 3.20×106 km2, compared to 6.46×106 km2 for the PI). On the other hand, there is little change for the maximum sea ice area (which is 15–16×106 km2 for both the PI and the LIG. To evaluate the model results we synthesise LIG sea ice data from marine cores collected in the Arctic Ocean, Nordic Seas and northern North Atlantic. The reconstructions for the northern North Atlantic show year-round ice-free conditions, and most models yield results in agreement with these reconstructions. Model–data disagreement appear for the sites in the Nordic Seas close to Greenland and at the edge of the Arctic Ocean. The northernmost site with good chronology, for which a sea ice concentration larger than 75 % is reconstructed even in summer, discriminates those models which simulate too little sea ice. However, the remaining models appear to simulate too much sea ice over the two sites south of the northernmost one, for which the reconstructed sea ice cover is seasonal. Hence models either underestimate or overestimate sea ice cover for the LIG, and their bias does not appear to be related to their bias for the pre-industrial period. Drivers for the inter-model differences are different phasing of the up and down short-wave anomalies over the Arctic Ocean, which are associated with differences in model albedo; possible cloud property differences, in terms of optical depth; and LIG ocean circulation changes which occur for some, but not all, LIG simulations. Finally, we note that inter-comparisons between the LIG simulations and simulations for future climate with moderate (1 % yr−1) CO2 increase show a relationship between LIG sea ice and sea ice simulated under CO2 increase around the years of doubling CO2. The LIG may therefore yield insight into likely 21st century Arctic sea ice changes using these LIG simulations.
- Published
- 2021
48. A data–model approach to interpreting speleothem oxygen isotope records from monsoon regions
- Author
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Parker, Sarah E., Harrison, Sandy P., Comas-Bru, Laia, Kaushal, Nikita, LeGrande, Allegra N., Werner, Martin, Parker, Sarah E., Harrison, Sandy P., Comas-Bru, Laia, Kaushal, Nikita, LeGrande, Allegra N., and Werner, Martin
- Abstract
Reconstruction of past changes in monsoon climate from speleothem oxygen isotope (δ18O) records is complex because δ18O signals can be influenced by multiple factors including changes in precipitation, precipitation recycling over land, temperature at the moisture source, and changes in the moisture source region and transport pathway. Here, we analyse > 150 speleothem records of the Speleothem Isotopes Synthesis and AnaLysis (SISAL) database to produce composite regional trends in δ18O in monsoon regions; compositing minimises the influence of site-specific karst and cave processes that can influence individual site records. We compare speleothem δ18O observations with isotope-enabled climate model simulations to investigate the specific climatic factors causing these regional trends. We focus on differences in δ18O signals between the mid-Holocene, the peak of the Last Interglacial (Marine Isotope Stage 5e) and the Last Glacial Maximum as well as on δ18O evolution through the Holocene. Differences in speleothem δ18O between the mid-Holocene and the Last Interglacial in the East Asian and Indian monsoons are small, despite the larger summer insolation values during the Last Interglacial. Last Glacial Maximum δ18O values are significantly less negative than interglacial values. Comparison with simulated glacial–interglacial δ18O shows that changes are principally driven by global shifts in temperature and regional precipitation. Holocene speleothem δ18O records show distinct and coherent regional trends. Trends are similar to summer insolation in India, China and southwestern South America, but they are different in the Indonesian–Australian region. Redundancy analysis shows that 37 % of Holocene variability can be accounted for by latitude and longitude, supporting the differentiation of records into individual monsoon regions. Regression analysis of simulated precipitation δ18O and climate variables show significant relationships between global Holocene monsoon δ1
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- 2021
49. The PMIP4 Last Glacial Maximum experiments: preliminary results and comparison with the PMIP3 simulations
- Author
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Kageyama, Masa, Harrison, Sandy P, Kapsch, Marie-L, Lofverstrom, Marcus, Lora, Juan M, Mikolajewicz, Uwe, Sherriff-Tadano, Sam, Vadsaria, Tristan, Abe-Ouchi, Ayako, Bouttes, Nathaelle, Chandan, Deepak, Gregoire, Lauren J., Ivanovic, Ruza F., Izumi, Kenji, LeGrande, Allegra N., Lhardy, Fanny, Lohmann, Gerrit, Morozova, Polina A., Ohgaito, Rumi, Paul, André, Peltier, W. Richard, Poulsen, Christopher J., Quiquet, Aurélien, Roche, Didier M, Shi, Xiaoxu, Tierney, Jessica E., Valdes, Paul J., Volodin, Evgeny, Zhu, Jiang, Kageyama, Masa, Harrison, Sandy P, Kapsch, Marie-L, Lofverstrom, Marcus, Lora, Juan M, Mikolajewicz, Uwe, Sherriff-Tadano, Sam, Vadsaria, Tristan, Abe-Ouchi, Ayako, Bouttes, Nathaelle, Chandan, Deepak, Gregoire, Lauren J., Ivanovic, Ruza F., Izumi, Kenji, LeGrande, Allegra N., Lhardy, Fanny, Lohmann, Gerrit, Morozova, Polina A., Ohgaito, Rumi, Paul, André, Peltier, W. Richard, Poulsen, Christopher J., Quiquet, Aurélien, Roche, Didier M, Shi, Xiaoxu, Tierney, Jessica E., Valdes, Paul J., Volodin, Evgeny, and Zhu, Jiang
- Abstract
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 Intercomparison Project (PMIP) contribution to the Coupled Model Intercomparison Project (CMIP). Here, we provide a preliminary analysis and evaluation of the results of these LGM experiments (PMIP4, most of which are PMIP4-CMIP6) and compare them with the previous generation of simulations (PMIP3, most of which are PMIP3-CMIP5). We show that the global averages of the PMIP4 simulations span a larger range in terms of mean annual surface air temperature and mean annual precipitation compared to the PMIP3-CMIP5 simulations, with some PMIP4 simulations reaching a globally colder and drier state. However, the multi-model global cooling average is similar for the PMIP4 and PMIP3 ensembles, while the multi-model PMIP4 mean annual precipitation average is drier than the PMIP3 one. There are important differences in both atmospheric and oceanic circulations between the two sets of experiments, with the northern and southern jet streams being more poleward and the changes in the Atlantic Meridional Overturning Circulation being less pronounced in the PMIP4-CMIP6 simulations than in the PMIP3-CMIP5 simulations. Changes in simulated precipitation patterns are influenced by both temperature and circulation changes. Differences in simulated climate between individual models remain large. Therefore, although there are differences in the average behaviour across the two ensembles, the new simulation results are not fundamentally different from the PMIP3-CMIP5 results. Evaluation of large-scale climate features, such as land–sea contrast and polar amplification, confirms that the models capture these well and within the uncertainty of the p
- Published
- 2021
50. Large-scale features of Last Interglacial climate: results from evaluating the lig127k simulations for the Coupled Model Intercomparison Project (CMIP6)–Paleoclimate Modeling Intercomparison Project (PMIP4)
- Author
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Otto-Bliesner, Bette L., Brady, Esther C., Zhao, Anni, Brierley, Chris M., Axford, Yarrow, Capron, Emilie, Govin, Aline, Hoffman, Jeremy S., Isaacs, Elizabeth, Kageyama, Masa, Scussolini, Paolo, Tzedakis, Polychronis C., Williams, Charles J. R., Wolff, Eric, Abe-Ouchi, Ayako, Braconnot, Pascale, Ramos Buarque, Silvana, Cao, Jian, de Vernal, Anne, Guarino, Maria Vittoria, Guo, Chuncheng, LeGrande, Allegra N., Lohmann, Gerrit, Meissner, Katrin J., Menviel, Laurie, Morozova, Polina A., Nisancioglu, Kerim H., O'ishi, Ryouta, Salas y Mélia, David, Shi, Xiaoxu, Sicard, Marie, Sime, Louise, Stepanek, Christian, Tomas, Robert, Volodin, Evgeny, Yeung, Nicholas K. H., Zhang, Qiong, Zhang, Zhongshi, Zheng, Weipeng, Otto-Bliesner, Bette L., Brady, Esther C., Zhao, Anni, Brierley, Chris M., Axford, Yarrow, Capron, Emilie, Govin, Aline, Hoffman, Jeremy S., Isaacs, Elizabeth, Kageyama, Masa, Scussolini, Paolo, Tzedakis, Polychronis C., Williams, Charles J. R., Wolff, Eric, Abe-Ouchi, Ayako, Braconnot, Pascale, Ramos Buarque, Silvana, Cao, Jian, de Vernal, Anne, Guarino, Maria Vittoria, Guo, Chuncheng, LeGrande, Allegra N., Lohmann, Gerrit, Meissner, Katrin J., Menviel, Laurie, Morozova, Polina A., Nisancioglu, Kerim H., O'ishi, Ryouta, Salas y Mélia, David, Shi, Xiaoxu, Sicard, Marie, Sime, Louise, Stepanek, Christian, Tomas, Robert, Volodin, Evgeny, Yeung, Nicholas K. H., Zhang, Qiong, Zhang, Zhongshi, and Zheng, Weipeng
- Abstract
The modeling of paleoclimate, using physically based tools, is increasingly seen as a strong out-of-sample test of the models that are used for the projection of future climate changes. New to the Coupled Model Intercomparison Project (CMIP6) is the Tier 1 Last Interglacial experiment for 127 000 years ago (lig127k), designed to address the climate responses to stronger orbital forcing than the midHolocene experiment, using the same state-of-the-art models as for the future and following a common experimental protocol. Here we present a first analysis of a multi-model ensemble of 17 climate models, all of which have completed the CMIP6 DECK (Diagnostic, Evaluation and Characterization of Klima) experiments. The equilibrium climate sensitivity (ECS) of these models varies from 1.8 to 5.6 ∘C. The seasonal character of the insolation anomalies results in strong summer warming over the Northern Hemisphere continents in the lig127k ensemble as compared to the CMIP6 piControl and much-reduced minimum sea ice in the Arctic. The multi-model results indicate enhanced summer monsoonal precipitation in the Northern Hemisphere and reductions in the Southern Hemisphere. These responses are greater in the lig127k than the CMIP6 midHolocene simulations as expected from the larger insolation anomalies at 127 than 6 ka. New synthesis for surface temperature and precipitation, targeted for 127 ka, have been developed for comparison to the multi-model ensemble. The lig127k model ensemble and data reconstructions are in good agreement for summer temperature anomalies over Canada, Scandinavia, and the North Atlantic and for precipitation over the Northern Hemisphere continents. The model–data comparisons and mismatches point to further study of the sensitivity of the simulations to uncertainties in the boundary conditions and of the uncertainties and sparse coverage in current proxy reconstructions. The CMIP6–Paleoclimate Modeling Intercomparison Project (PMIP4) lig127k simulations, in
- Published
- 2021
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