Possible pathways to a Dansgaard-Oeschger (DO) PMIP protocol

2021 ◽  
Author(s):  
Irene Malmierca-Vallet ◽  
Louise C. Sime ◽  
Paul J. Valdes
Keyword(s):  
General Circulation ◽  
Climate Changes ◽  
General Circulation Models ◽  
Ice Age ◽  
Climate Change Projections ◽  
The Past ◽  
External Perturbations ◽  
Mis 3 ◽  
Last Ice Age ◽  
Earth System Models

<p>The DO events of the last ice age represent one of the best studied abrupt climate transitions, yet we still lack a comprehensive explanation for them. There is uncertainty whether current IPCC-relevant models can effectively represent the processes that cause DO events. Current Earth system models (ESMs) seem overly stable against external perturbations and incapable of reproducing most abrupt climate changes of the past (Valdes, 2011). If this holds true, this could noticeably influence their capability to predict future abrupt transitions, with significant consequences for the delivery of precise climate change projections.  In this task, the objectives of this study are (1) to cross compare existing simulations that show spontaneous DO-type oscillations using a common set of diagnostics so we can compare the mechanisms and the characteristics of the oscillations, and (2) to formulate possible pathways to a DO PMIP protocol that could help investigate cold-period instabilities through a range of insolation-, freshwater-, GHG-, and NH ice sheet-related forcings, as well as evaluating the possibility of spontaneous internal oscillations.</p><p>Although most abrupt DO events happened during MIS3, only few studies investigate DO events in coupled general circulation models under MIS 3 conditions (e.g., Kawamura et al., 2017; Zhang and Prange, 2020). Here, we thus propose that the MIS3 period could be the focus of such a DO-event modelling protocol. More specific sensitivity experiments performed under MIS 3 boundary conditions are needed in order to (1) better understand the mechanisms behind millennial-scale climate variability, (2) explore AMOC variability under intermediate glacial conditions, and (3) help answer the question: “are models too stable?”.</p>

Dansgaard-Oeschger Tipping Events (TEs): Towards determining if IPCC-relevant models represent these TEs.

2021 ◽  
Author(s):  
Louise Sime ◽  
Irene Malmierca Vallet ◽  
Paul Valdes
Keyword(s):  
General Circulation ◽  
General Circulation Models ◽  
Last Glacial Period ◽  
Mis 3 ◽  
Common Framework ◽  
Intercomparison Project ◽  
Earth System Models ◽  
Paleoclimate Modelling ◽  
The Last Glacial ◽  
Millennial Scale

<p>Dansgaard-Oeschger (DO) events are abrupt, large climate swings that punctuated the last glacial period. There is uncertainty whether current IPCC-relevant models can effectively represent the processes that cause DO events. This has implications for whether these models are also capable of simulating future TEs,  and more in general, for the delivery of accurate climate change projections. Here we present progress on possible pathways to a DO Paleoclimate Modelling Intercomparison Project (PMIP) protocol. This is broad interest to the climate community since (1), there is currently no PMIP common guidance to investigate DO events, (2) it could help carry out simulations in Earth system models under a common framework, and (3) it will help guide a more methodical search for DO events in current models. A protocol could help investigate cold-period TEs through a range of insolation-, freshwater-, green-house-gas-, and Northern Hemisphere ice sheet-related forcings, as well as evaluating the possibility of spontaneous TEs. MIS3 was a period of noticeable millennial-scale climate variability, characterised by the most regular incidence of DO events (Schulz et al., 1999). Although most abrupt DO events happened during MIS3, only few studies investigate TEs in coupled general circulation models under MIS 3 conditions (e.g., Kawamura et al., 2017; Zhang and Prange, 2020). Here, we therefore suggest that the MIS3 period could be the focus of such a DO-event focussed modelling protocol. Experiments performed under MIS 3 boundary conditions may help (1) explore variability under intermediate glacial conditions, (2) better understand the mechanisms behind millennial-scale TEs, (3) look for spontaneous DO-type oscillations, and (4) help answer the question: “are models too stable?”.</p>

scholarly journals Plankton, from the last ice age to the year 3007

2008 ◽  
Vol 65 (3) ◽  
pp. 296-301 ◽  
Author(s):  
E. C. Pielou
Keyword(s):  
Positive Feedback ◽  
Climate Changes ◽  
Thermohaline Circulation ◽  
Canadian Arctic ◽  
Ice Age ◽  
Climate Forcing ◽  
The Arctic ◽  
Mackenzie Delta ◽  
The Past ◽  
Last Ice Age

Abstract Pielou, E. C. 2008. Plankton, from the last ice age to the year 3007. – ICES Journal of Marine Science, 65: 296–301. Climate forcing of the environment and biota has been happening since time immemorial, human forcing only for the past 200 years or so. This paper considers, first, climatic changes over the past 30 000 years, as indicated by plankton and their effects on plankton. Only fossilizable plankton can be observed: principally foraminifera, radiolaria, and pteropods in the zooplankton, and their food, principally coccolithophores, diatoms, and dinoflagellate cysts, in the phytoplankton. The soft-bodied zooplankton species—especially copepods—that lived with them can only be inferred. Large, abrupt climate changes took place, aided by positive feedback. Second, this paper attempts to predict how human forcing in the form of anthropogenic climate change is likely to affect marine ecosystems in the future. Past predictions have underestimated the speed at which warming is actually happening: positive feedback has been unexpectedly strong. Thus, the melting of snow and ice, by reducing the earth's albedo, has increased the amount of solar energy absorbed. Also, warming of the surface (water and land) has caused outgassing of methane from buried clathrates (hydrates), and methane is a strong greenhouse gas. Currently, predictions emphasize one or the other of two contrasted alternatives: abrupt cooling caused by a shutdown of the thermohaline circulation (the “ocean conveyor”) or abrupt warming caused by copious outgassing of methane. Both arguments (the former from oceanographers and the latter from geophysicists) are equally persuasive, and I have chosen to explore the methane alternative, because I am familiar with an area (the Beaufort Sea and Mackenzie Delta) where outgassing has recently (2007) been detected and is happening now: in the Arctic Ocean and the Canadian Arctic Archipelago, where disappearance of the ice will affect currents, temperature, thermocline, salinity, upwelling, and nutrients, with consequent effects on the zooplankton.

Modelling of palaeoclimates: examples from the recent past

1993 ◽  
Vol 341 (1297) ◽  
pp. 267-275 ◽  
Keyword(s):  
General Circulation ◽  
Three Dimensional ◽  
General Circulation Models ◽  
Ice Age ◽  
Atmospheric Composition ◽  
Equilibrium Studies ◽  
Orbital Parameters ◽  
Last Ice Age ◽  
The Last Glacial Maximum ◽  
The Last Glacial

Three-dimensional general circulation models have been used in equilibrium studies of past climates by fixing the slowly changing parts of the climate system (orbital parameters, ice sheets, atmospheric composition; Results are presented from studies of the m id-Holocene, the last glacial maximum and the initiation of the last ice age.

scholarly journals Historical droughts in Mediterranean regions during the last 500 years: a data/model approach

2007 ◽  
Vol 3 (2) ◽  
pp. 355-366 ◽  
Author(s):  
S. Brewer ◽  
S. Alleaume ◽  
J. Guiot ◽  
A. Nicault
Keyword(s):  
Drought Stress ◽  
General Circulation ◽  
Distance Measure ◽  
Severity Index ◽  
General Circulation Models ◽  
Ice Age ◽  
Drought Severity ◽  
Atmospheric Circulation Patterns ◽  
Dry Conditions ◽  
Simulated Climate

Abstract. We present here a new method for comparing the output of General Circulation Models (GCMs) with proxy-based reconstructions, using time series of reconstructed and simulated climate parameters. The method uses k-means clustering to allow comparison between different periods that have similar spatial patterns, and a fuzzy logic-based distance measure in order to take reconstruction errors into account. The method has been used to test two coupled ocean-atmosphere GCMs over the Mediterranean region for the last 500 years, using an index of drought stress, the Palmer Drought Severity Index. The results showed that, whilst no model exactly simulated the reconstructed changes, all simulations were an improvement over using the mean climate, and a good match was found after 1650 with a model run that took into account changes in volcanic forcing, solar irradiance, and greenhouse gases. A more detailed investigation of the output of this model showed the existence of a set of atmospheric circulation patterns linked to the patterns of drought stress: 1) a blocking pattern over northern Europe linked to dry conditions in the south prior to the Little Ice Age (LIA) and during the 20th century; 2) a NAO-positive like pattern with increased westerlies during the LIA; 3) a NAO-negative like period shown in the model prior to the LIA, but that occurs most frequently in the data during the LIA. The results of the comparison show the improvement in simulated climate as various forcings are included and help to understand the atmospheric changes that are linked to the observed reconstructed climate changes.

Ensemble climate predictions using climate models and observational constraints

2007 ◽  
Vol 365 (1857) ◽  
pp. 2029-2052 ◽  
Author(s):  
Peter A Stott ◽  
Chris E Forest
Keyword(s):  
Climate Change ◽  
General Circulation ◽  
Climate Changes ◽  
Climate Models ◽  
State Of The Art ◽  
General Circulation Models ◽  
Computationally Efficient ◽  
Temperature Changes ◽  
Large Ensembles ◽  
Past Climate Change

Two different approaches are described for constraining climate predictions based on observations of past climate change. The first uses large ensembles of simulations from computationally efficient models and the second uses small ensembles from state-of-the-art coupled ocean–atmosphere general circulation models. Each approach is described and the advantages of each are discussed. When compared, the two approaches are shown to give consistent ranges for future temperature changes. The consistency of these results, when obtained using independent techniques, demonstrates that past observed climate changes provide robust constraints on probable future climate changes. Such probabilistic predictions are useful for communities seeking to adapt to future change as well as providing important information for devising strategies for mitigating climate change.

scholarly journals Historical droughts in Mediterranean regions during the last 500 years: a data/model approach

2006 ◽  
Vol 2 (5) ◽  
pp. 771-800 ◽  
Author(s):  
S. Brewer ◽  
S. Alleaume ◽  
J. Guiot ◽  
A. Nicault
Keyword(s):  
Drought Stress ◽  
General Circulation ◽  
Distance Measure ◽  
Severity Index ◽  
General Circulation Models ◽  
Ice Age ◽  
Drought Severity ◽  
Atmospheric Circulation Patterns ◽  
Mediterranean Regions ◽  
Dry Conditions

Abstract. We present here a new method for comparing the output of General Circulation Models (GCMs) with proxy-based reconstructions, using time series of reconstructed and simulated climate parameters. The method uses k-means clustering to allow comparison between different periods that have similar spatial patterns, and a fuzzy logic-based distance measure in order to take reconstruction errors into account. The method has been used to test two coupled ocean-atmosphere GCMs over the Mediterranean region for the last 500 years, using an index of drought stress, the Palmer Drought Severity Index. The results showed that, whilst no model was able to exactly simulate the reconstructed changes, all simulations were an improvement over using the mean climate. Further, a good match was found after 1650 with a model run that took into account changes in volcanic forcing, solar irradiance, and greenhouse gases. A more detailed investigation of the output of this model showed the existence of a set of atmospheric circulation patterns linked to the patterns of drought stress: 1) a blocking pattern over northern Europe linked to dry conditions in the south prior to the Little Ice Age (LIA) and during the 20th century; 2) a NAO-positive like pattern with increased westerlies during the LIA; 3) a NAO-negative like period shown in the model prior to the LIA, but that occurs most frequently in the data during this period. The results of the comparison emphasise the importance of the inclusion of the various forcings in the models and help to understand the atmospheric changes connected to reconstructed climate changes.

scholarly journals In Anticipation of Extirpation

2020 ◽  
Vol 12 (1) ◽  
pp. 113-131 ◽  
Author(s):  
Patrick D. Nunn
Keyword(s):  
Sea Level Rise ◽  
Sea Level ◽  
Ice Age ◽  
Optimal Solutions ◽  
The Holocene ◽  
The Past ◽  
Coastal Cities ◽  
The People ◽  
Northwest Europe ◽  
Last Ice Age

Abstract As concern about sea level rise grows and optimal solutions are sought to address its causes and effects, little attention has been given to past analogs. This article argues that valuable insights into contemporary discussions about future sea level rise can be gained from understanding those of the past, specifically the ways in which coastal peoples and societies reacted during the period of postglacial sea level rise. For much of the Holocene, most continental people eschewed coastal living in favor of inland areas. In many places large coastal settlements appeared only after the development of polities and associated crosswater networks. Postglacial sea level rise affected coastal living in ways about which we remain largely ignorant. Yet, millennia-old stories from Australia and northwest Europe show how people responded, from which we can plausibly infer their motivations. Stories from Australia say the people have succeeded in halting sea level rise, whereas those from northwest Europe indicate that people have failed, leading to the drowning of coastal cities such as Ys (Brittany) and Cantre’r Gwaelod (Wales). This distinction is explained by the contrasting duration of postglacial sea level rise in these regions; around Australia, sea level stopped rising 7,000 years ago, while along many coasts of northwest Europe it has risen unceasingly since the last ice age ended. The nature of past human and societal responses to postglacial sea level rise holds important insights for the future.

The Advent of Climate Science

2020 ◽  
Author(s):  
Deborah R. Coen
Keyword(s):  
Research Program ◽  
General Circulation ◽  
Modern Science ◽  
Climate Science ◽  
General Circulation Models ◽  
World War ◽  
The Past ◽  
Measurement And Analysis ◽  
History Of ◽  
Definition Of

The advent of climate science can be defined as the historical emergence of a research program to study climate according to a modern definition of climate. Climate in this sense: (1) refers not simply to the average state of the atmosphere but also to its variability; (2) is multiscalar, concerned with phenomena ranging from the very small and fast to the very large and slow; and (3) is understood to be influenced by the oceans, lithosphere, cryosphere, and biosphere. Most accounts of the history of climate science to date have focused on the development of computerized general circulation models since World War Two. However, following this definition, the advent of climate science occurred well before the computer age. This entry therefore seeks to dispel the image of climate science as a recent invention and as the preserve of an exclusive, North American elite. The historical roots of today’s knowledge of climate change stretch surprisingly far back into the past and clear across the world, though the geographic focus here is on Europe and North America. The modern science of climate emerged out of interactions between learned and vernacular knowledge traditions, and has simultaneously appropriated and undermined traditional and indigenous forms of climate knowledge. Important precedents emerged in the 17th and 18th centuries, and it was in the late 19th century that a modern science of climate coalesced into a coordinated research program in part through the unification of divergent knowledge traditions around standardized techniques of measurement and analysis.

scholarly journals Spatiotemporal Trends and Attribution of Drought across China from 1901–2100

2020 ◽  
Vol 12 (2) ◽  
pp. 477
Author(s):  
Yongxia Ding ◽  
Shouzhang Peng
Keyword(s):  
Adverse Effects ◽  
General Circulation ◽  
Potential Evapotranspiration ◽  
Northern China ◽  
General Circulation Models ◽  
Research Unit ◽  
Mitigation Strategies ◽  
Climatic Research Unit ◽  
The Past ◽  
Spatiotemporal Trends

Investigating long-term drought trends is of great importance in coping with the adverse effects of global warming. However, little attention has been focused on studying the detailed spatial variability and attribution of drought variation in China. In this study, we first generated a 1 km resolution monthly climate dataset for the period 1901–2100 across China using the delta spatial downscaling method to assess the variability of the Standardized Precipitation Evaporation Index (SPEI). We then developed a simple approach to quantifying the contributions of water supply (precipitation) and demand (potential evapotranspiration, PET) on SPEI variability, according to the meaning of the differentiating SPEI equation. The results indicated that the delta framework could accurately downscale and correct low-spatial-resolution monthly temperatures and precipitation from the Climatic Research Unit and general circulation models (GCMs). Of the 27 GCMs analyzed, the BNU-ESM, CESM1-CAM5, and GFDL-ESM2M were found to be the most accurate in modeling future temperatures and precipitation. We also found that, compared with the past (1901–2017), the climate in the future (2018–2100) will tend toward significant droughts, although both periods showed a high spatial heterogeneity across China. Moreover, the proportion of areas with significantly decreasing SPEI trends was far greater than the proportion of those with increasing trends in most cases, especially for northwestern and northern China. Finally, the proposed approach to quantifying precipitation and PET contributions performed well according to logical evaluations. The percentage contributions of precipitation and PET on SPEI variability varied with study periods, representative concentration pathway scenarios, trend directions, and geographic spaces. In the past, PET contributions for significant downward trends and precipitation contributions for significantly upward trends accounted for 95% and 72%, while their future contributions were 57 ± 22%–149 ± 20% and 95 ± 27%–190 ± 58%, respectively. Overall, our results provide detailed insights for planning flexible adaptation and mitigation strategies to cope with the adverse effects of climate drought across China.

Geomorphological Development of the Memphite Floodplain Over the Past 6,000 Years

2013 ◽  
Vol 30 (2) ◽  
pp. 61-67 ◽  
Author(s):  
Judith Bunbury
Keyword(s):  
Landscape Change ◽  
Ice Age ◽  
Landscape Changes ◽  
River Systems ◽  
The Past ◽  
Landscape Processes ◽  
Northern Egypt ◽  
Last Ice Age ◽  
River Migration

Abstract The Memphite ruin mounds around the modern town of Mit Rahina in northern Egypt form a part of a region around which the capital of Egypt mi grated through time. Some of these migrations were the responses to landscape changes and the area is one that is subject to a number of types of landscape change. The delta and river systems as well as the deserts that surround Memphis changed profoundly as global temperatures rose at theend of the last ice age. This paper summarises the main landscape processes that affected the area and pro poses a model for river migration and delta-head change in the Memphite floodplain.

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