scholarly journals Past terrestrial hydroclimate driven by Earth System Feedbacks

2021 ◽  
Author(s):  
Ran Feng
Keyword(s):  
Ice Sheets ◽  
Sedimentary Facies ◽  
Stationary Wave ◽  
Earth System ◽  
Surface Warming ◽  
Warming Pattern ◽  
Northern High Latitude ◽  
Major Loss ◽  
Co2 Level ◽  
High Lake Levels

Geologic evidence suggests drastic reorganizations of subtropical terrestrial hydroclimate during past warm intervals, including the mid-Piacenzian Warm Period (MP, 3.3 to 3.0 Ma). Despite having a similar to present-day atmospheric CO2 level (pCO2), MP featured moist subtropical conditions with high lake levels in Northern Africa, and mesic vegetation and sedimentary facies in subtropical Eurasia. Here, we demonstrate that major loss of the northern high-latitude ice sheets and continental greening, not the pCO2 forcing, are key to generating moist terrestrial conditions in subtropical Sahel and east Asia. In contrast to previous hypotheses, the moist conditions simulated in both regions are a product of enhanced tropospheric humidity and a stationary wave response to the surface warming pattern, both varying strongly in response to land cover changes. These results suggest that past terrestrial hydroclimate states were driven by Earth System Feedbacks, which may outweigh the direct effect of pCO2 forcing.

Mid-Pliocene mesic subtropical hydroclimate over continents driven by land surface changes

2021 ◽  
Author(s):  
Ran Feng ◽  
Tripti Bhattacharya ◽  
Bette Otto-bliesner ◽  
Esther Brady ◽  
Keyword(s):  
Land Surface ◽  
Atmospheric Carbon Dioxide ◽  
Hadley Circulation ◽  
Stationary Wave ◽  
Wave Pattern ◽  
Earth System ◽  
Surface Warming ◽  
Warming Pattern ◽  
Earth System Models ◽  
Surface Changes

<p>Earth System Models (ESMs) project drying of the northern subtropics by the end of the 21<sup>st</sup> century. However, geologic evidence from intervals with elevated concentrations of atmospheric carbon dioxide (pCO<sub>2</sub>), like the mid-Pliocene, suggest mesic subtropical conditions. Several hypotheses, including an El Niño-like SST pattern and weaker Hadley circulation, have been proposed to explain this mismatch. Here, we show that PlioMIP2 ensemble broadly capture the pattern of proxy reconstructed Pliocene hydroclimate, notably a wetter Sahel and southeast Asia. Sensitivity simulations reveal that this pattern is driven by summertime rainfall increases as a result of lowered albedo and a distinct surface warming pattern, generated by prescribed vegetation and ice sheet changes. The resultant tropospheric moistening and stationary wave pattern enhance moisture convergence into the northern subtropics. Our results suggest that mid-Pliocene hydroclimate is part of the Earth system feedback to sustained CO<sub>2</sub> concentrations similar to today.</p><p><img src="https://contentmanager.copernicus.org/fileStorageProxy.php?f=gepj.0005b442a70068203111161/sdaolpUECMynit/12UGE&app=m&a=0&c=d33f4ac1a0750ab37681b00412fa7633&ct=x&pn=gepj.elif&d=1" alt=""></p>

scholarly journals Instability of Northeast Siberian ice sheet during glacials

2018 ◽  
Author(s):  
Zhongshi Zhang ◽  
Qing Yan ◽  
Elizabeth J. Farmer ◽  
Camille Li ◽  
Gilles Ramstein ◽  
...  
Keyword(s):  
North America ◽  
Ice Sheets ◽  
Ice Sheet ◽  
Stationary Wave ◽  
Wave Pattern ◽  
Ocean Dynamics ◽  
Stationary Waves ◽  
Surface Warming ◽  
The North ◽  
East Siberian Sea

Abstract. It has been widely believed that Northeast (NE) Siberia remained ice-free during most Pleistocene Northern Hemisphere (NH) glaciations, while ice sheets extended gradually across North America and Northwest (NW) Eurasia. However, recent fieldwork has provided robust evidence of ice sheets occupying the shallow continental shelf of the East Siberian Sea during several Pleistocene glaciations. The debate surrounding the existence and history of this enigmatic NE Siberian ice sheet highlights fundamental gaps in our current understanding of the mechanisms of glacial climate evolution. Here, we combine climate and ice sheet simulations to demonstrate how ice-vegetation-atmosphere-ocean dynamics can lead to two ice sheet configurations: the well-known Laurentide-Eurasian configuration with large ice sheets over North America and NW Eurasia, and a circum-Arctic configuration with large ice sheets over NE Siberia and the Canadian Rockies. Compared to the Laurentide-Eurasian configuration, formation of the circum-Arctic configuration can occur with an atmospheric stationary wave pattern similar to today's. Once the circum-Arctic configuration is established, it amplifies atmospheric stationary waves, leading to surface warming in the North Pacific, ablation of the NE Siberian ice sheet, and ultimately a swing to the Laurentide-Eurasian configuration. Our simulations highlight the complexity of glacial climates, and may hint towards potential mechanisms for interglacial-glacial transitions.

scholarly journals Sensitivity of Global Warming to Carbon Emissions: Effects of Heat and Carbon Uptake in a Suite of Earth System Models

2017 ◽  
Vol 30 (23) ◽  
pp. 9343-9363 ◽  
Author(s):  
Richard G. Williams ◽  
Vassil Roussenov ◽  
Philip Goodwin ◽  
Laure Resplandy ◽  
Laurent Bopp
Keyword(s):  
Climate Sensitivity ◽  
Carbon Emissions ◽  
Radiative Forcing ◽  
Carbon Uptake ◽  
Earth System ◽  
Ocean Heat Uptake ◽  
Surface Warming ◽  
System Models ◽  
Heat Uptake ◽  
Earth System Models

Climate projections reveal global-mean surface warming increasing nearly linearly with cumulative carbon emissions. The sensitivity of surface warming to carbon emissions is interpreted in terms of a product of three terms: the dependence of surface warming on radiative forcing, the fractional radiative forcing from CO2, and the dependence of radiative forcing from CO2 on carbon emissions. Mechanistically each term varies, respectively, with climate sensitivity and ocean heat uptake, radiative forcing contributions, and ocean and terrestrial carbon uptake. The sensitivity of surface warming to fossil-fuel carbon emissions is examined using an ensemble of Earth system models, forced either by an annual increase in atmospheric CO2 or by RCPs until year 2100. The sensitivity of surface warming to carbon emissions is controlled by a temporal decrease in the dependence of radiative forcing from CO2 on carbon emissions, which is partly offset by a temporal increase in the dependence of surface warming on radiative forcing. The decrease in the dependence of radiative forcing from CO2 is due to a decline in the ratio of the global ocean carbon undersaturation to carbon emissions, while the increase in the dependence of surface warming is due to a decline in the ratio of ocean heat uptake to radiative forcing. At the present time, there are large intermodel differences in the sensitivity in surface warming to carbon emissions, which are mainly due to uncertainties in the climate sensitivity and ocean heat uptake. These uncertainties undermine the ability to predict how much carbon may be emitted before reaching a warming target.

Global Maps of Lake-Level Fluctuations since 30,000 yr B.P.

1979 ◽  
Vol 12 (1) ◽  
pp. 83-118 ◽  
Author(s):  
F. Alayne Street ◽  
A. T. Grove
Keyword(s):  
Lake Level ◽  
Ice Sheets ◽  
Literature Survey ◽  
Sea Surface ◽  
Lake Levels ◽  
Lake Level Fluctuations ◽  
Average Abundance ◽  
The Tropics ◽  
High Lake Levels ◽  
Precipitation And Temperature

This paper presents selected world maps of lake-level fluctuations since 30,000 yr B.P. These are based on a literature survey of 141 lake basins with radiocarbon-dated chronologies. The resulting patterns are subcontinental in scale and show orderly variations in space and time. They reflect substantial changes in continental precipitation, evaporation, and runoff, which are due to glacial/interglacial fluctuations in the atmospheric and oceanic circulations. In the tropics, high lake levels are essentially an interglacial or interstadial phenomenon, although there are important exceptions. Since extensive lakes during the Holocene corresponded with relatively high sea-surface temperatures, and therefore presumably with high evaporation rates on land, they are interpreted as the result of higher precipitation. Tropical aridity culminated in most areas at, or just after, the glacial maximum, although the present day is also characterized by a below-average abundance of surface water. In extratropical regions the mapped patterns are more complex. They vary markedly with latitude and proximity to major ice sheets. In these areas, evidence is at present insufficient to evaluate the relative contributions of precipitation and temperature to the observed lake-level record.

scholarly journals Semi-Lagrangian transport of oxygen isotopes in polythermal ice sheets: implementation and first results

2014 ◽  
Vol 7 (1) ◽  
pp. 1137-1174 ◽  
Author(s):  
T. Goelles ◽  
K. Grosfeld ◽  
G. Lohmann
Keyword(s):  
Hydrological Cycle ◽  
Ice Sheets ◽  
Ice Sheet ◽  
Ice Cores ◽  
Earth System ◽  
Tracer Transport ◽  
Stable Water Isotopes ◽  
Lagrangian Transport ◽  
Driving Mechanisms ◽  
Earth’S System

Abstract. Modelling the evolution of the Earth system on long timescales requires the knowledge and understanding of driving mechanisms, such as the hydrological cycle. This is dominant in all components of the Earth's system, such as atmosphere, ocean, land surfaces/vegetation and the cryosphere. Observations and measurements of stable water isotopes in climate archives can help to decipher and reconstruct climate change and its regional variations. For the cryosphere, the δ18O cycle in the current generation of Earth-System-Models is missing and an efficient and accurate tracer transport scheme is required. We describe ISOPOLIS 1.0 a modular semi-Lagrangian transport scheme of second order accuracy which is coupled to the polythermal and thermomechanical ice sheet model SICOPOLIS (version 2.9). Model skill is demonstrated by experiments with a simplified ice sheet geometry and by comparisons of simulated ice cores with data from Greenland (GRIP) and Antarctica (Vostok). The presented method is a valuable tool to investigate the transport of any kind of passive tracer inside polythermal ice sheets and is an important step to model the whole δ18O cycle.

scholarly journals A kinematic formalism for tracking ice–ocean mass exchange on the Earth's surface and estimating sea-level change

2020 ◽  
Vol 14 (9) ◽  
pp. 2819-2833
Author(s):  
Surendra Adhikari ◽  
Erik R. Ivins ◽  
Eric Larour ◽  
Lambert Caron ◽  
Helene Seroussi
Keyword(s):  
Solid Earth ◽  
Sea Level ◽  
Mass Exchange ◽  
Ice Sheets ◽  
Earth System ◽  
Generic Level ◽  
Ocean Mass ◽  
Geophysical Processes ◽  
Ice Sheet Dynamics ◽  
And Sea Level

Abstract. Polar ice sheets are important components of the Earth system. As the geometries of land, ocean and ice sheets evolve, they must be consistently captured within the lexicon of geodesy. Understanding the interplay between the processes such as ice-sheet dynamics, solid-Earth deformation, and sea-level adjustment requires both geodetically consistent and mass-conserving descriptions of evolving land and ocean domains, grounded ice sheets and floating ice shelves, and their respective interfaces. Here we present mathematical descriptions of a generic level set that can be used to track both the grounding lines and coastlines, in light of ice–ocean mass exchange and complex feedbacks from the solid Earth and sea level. We next present a unified method to accurately compute the sea-level contribution of evolving ice sheets based on the change in ice thickness, bedrock elevation and mean sea level caused by any geophysical processes. Our formalism can be applied to arbitrary geometries and at all timescales. While it can be used for applications with modeling, observations and the combination of two, it is best suited for Earth system models, comprising ice sheets, solid Earth and sea level, that seek to conserve mass.

Simulation of LGM ice sheets with the Community Earth System Model version 2 

2021 ◽  
Author(s):  
Sarah L Bradley ◽  
Michele Petrini ◽  
Raymond Sellevold ◽  
Miren Vizcaino ◽  
William H. Lipscomb ◽  
...  
Keyword(s):  
Ice Sheets ◽  
Ice Sheet ◽  
Earth System Model ◽  
System Model ◽  
Earth System ◽  
Last Deglaciation ◽  
Model Version ◽  
Starting Point ◽  
Community Earth System Model ◽  
The Last Deglaciation

<p>The last deglaciation provides as unique a framework to investigate the processes of ice sheet and climate interaction during periods of mass loss as in the current climate. Here we simulate the Last Glacial Maximum (LGM) northern hemisphere ice sheets climate, surface mass balance (SMB), and dynamics with the Community Earth System Model version 2 (CESM2, Danabasoglu et al., 2020)) and the Community Ice Sheet Model version 2 (CISM2, Lipscomb et al., 2019). This LGM simulation will be later used as starting point for coupled CESM2-CISM2 simulations of the last deglaciation.</p><p> </p><p>CESM2 is run at the nominal resolution used for IPCC-type projections (approx. 1 degree for all components). The model includes an advanced snow/firn and SMB calculation (van Kampenhout et al, 2019; Sellevold et al, 2019) the land component (CLM, cite) that has been evaluated and applied to the simulation of the future Greenland melt (van Kampenhout et al, 2020, Muntjewerf et al., 2020a,b, Sellevold & Vizcaino, 2020).</p><p> </p><p>Our analysis examines how the global, Arctic, and North Atlantic climate result in the simulated radiative and turbulent heat fluxes over the ice sheets, and the mass fluxes from precipitation, refreezing, runoff, and sublimation. We also examine the simulated ice streams in CISM2, which is run at 8 km under a higher-order approximation for ice flow.</p>

The role of efficient climate models in the projection of future climate feedback and surface warming

2021 ◽  
Author(s):  
Philip Goodwin ◽  
B.B. Cael
Keyword(s):  
Climate Model ◽  
Climate Feedback ◽  
Model Output ◽  
Earth System ◽  
Surface Warming ◽  
System Models ◽  
Model Ensembles ◽  
Computational Resources ◽  
Earth System Models ◽  
Global Mean

<p>Projecting the global climate feedback and surface warming responses to anthropogenic forcing scenarios remains a key priority for climate science. Here, we explore possible roles for efficient climate model ensembles in contributing to quantitative projections of future global mean surface warming and climate feedback within model hierarchies. By comparing complex and efficient (sometimes termed ‘simple’) model output to data we: (1) explore potential Bayesian approaches to model ensemble generation; (2) ask what properties an efficient climate model should have to contribute to the generation of future warming and climate feedback projections; (3) present new projections from efficient model ensembles.</p><p> </p><p>Climate processes relevant to global surface warming and climate feedback act over at least 14 orders of magnitude in space and time; from cloud droplet collisions and photosynthesis up to the global mean temperature and carbon storage over the 21<sup>st</sup> century. Due to computational resources, even the most complex Earth system models only resolve around 3 orders of magnitude in horizontal space (from grid scale up to global scale) and 6 orders of magnitude in time (from a single timestep up to a century).</p><p> </p><p>Complex Earth system models must therefore contain a great many parameterisations (including specified functional forms of equations and their coefficient values) representing sub grid-scale and sub time-scale processes. We know that these parameterisations affect the <em>quantitative</em> model projections, because different complex models produce a range of historic and future projections. However, complex Earth system models are too computationally expensive to fully sample the plausible combinations of their own parameterisations, typically being able to realise only several tens of simulations.</p><p> </p><p>In contrast, efficient climate models are able to utilise computational resources to resolve their own plausible combinations of parameterisations, through the construction of very large model ensembles. However, this parameterisation resolution occurs at the expense of a much-reduced resolution of relevant climate processes. Since the relative simplicity of efficient model representations may not capture the required complexity of the climate system, the <em>qualitative</em> nature of their simulated projections may be too simplistic. For example, an efficient climate model may use a single climate feedback value for all time and for all sources of radiative forcing, when in complex models (and the real climate system) climate feedbacks may vary over time and may respond differently to, say, localised aerosol forcing than to well mixed greenhouse gases.</p><p> </p><p>By far the dominant quantitative projections of global mean surface warming in the scientific literature, as used in the Intergovernmental Panel on Climate Change Assessment Reports, derive from relatively small ensembles of complex climate model output. However, computational resources impose an inherent trade-off between model resolution of relevant climate processes (affecting the qualitative nature of the model framework) and model ensemble resolution of plausible parameterisations (affecting the quantitative exploration of projections within that model framework). This computationally imposed trade-off suggests there may be a significant role for efficient model output, within a hierarchy of model complexities, when generating future warming projections.</p>

Dynamic Effect of Last Glacial Maximum Ice Sheet Topography on the East Asian Summer Monsoon

2020 ◽  
Vol 33 (16) ◽  
pp. 6929-6944 ◽  
Author(s):  
Yu Gao ◽  
Zhengyu Liu ◽  
Zhengyao Lu
Keyword(s):  
Summer Monsoon ◽  
East Asian Summer Monsoon ◽  
Asian Summer Monsoon ◽  
East Asian ◽  
Ice Sheets ◽  
Ice Sheet ◽  
Stationary Wave ◽  
Westerly Jet ◽  
Asian Summer ◽  
Ice Sheet Topography

AbstractThe effect of ice sheet topography on the East Asian summer monsoon (EASM) during the Last Glacial Maximum is studied using CCSM3 in a hierarchy of model configurations. It is found that receding ice sheets result in a weakened EASM, with the reduced ice sheet thickness playing a major role. The lower ice sheet topography weakens the EASM through shifting the position of the midlatitude jet, and through altering Northern Hemisphere stationary waves. In the jet shifting mechanism, the lowering of ice sheets shifts the westerly jet northward and decreases the westerly jet over the subtropics in summer, which reduces the advection of dry enthalpy and in turn precipitation over the EASM region. In the stationary wave mechanism, the lowering of ice sheets induces an anomalous stationary wave train along the westerly waveguide that propagates into the EASM region, generating an equivalent-barotropic low response; this leads to reduced lower-tropospheric southerlies, which in turn reduces the dry enthalpy advection into East Asia, and hence the EASM precipitation.

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