AMOC stability and diverging response to Arctic sea ice decline in two climate models

2021 ◽  
pp. 1-47
Author(s):  
Hui Li ◽  
Alexey Fedorov ◽  
Wei Liu
Keyword(s):  
Sea Ice ◽  
Climate Models ◽  
Horizontal Resolution ◽  
Arctic Sea Ice ◽  
Meridional Overturning Circulation ◽  
Quasi Equilibrium ◽  
Freshwater Transport ◽  
Sea Ice Decline ◽  
Basin Scale ◽  
Arctic Sea

AbstractThis study compares the impacts of Arctic sea ice decline on the Atlantic Meridional Overturning Circulation (AMOC) in two configurations of the Community Earth System Model (CESM) with different horizontal resolution. In a suite of model experiments we impose radiative imbalance at the ice surface, replicating a loss of sea ice cover comparable to the observed during 1979-2014, and find dramatic differences in the AMOC response between the two models. In the lower-resolution configuration, the AMOC weakens by about one third over the first 100 years, approaching a new quasi-equilibrium. By contrast, in the higher-resolution configuration, the AMOC weakens by ~10% during the first 20-30 years followed by a full recovery driven by invigorated deep water formation in the Labrador Sea and adjacent regions. We investigate these differences using a diagnostic AMOC stability indicator, which reflects the AMOC freshwater transport in and out of the basin and hence the strength of the basin-scale salt-advection feedback. This indicator suggests that the AMOC in the lower-resolution model is less stable and more sensitive to surface perturbations, as confirmed by hosing experiments mimicking Arctic freshening due to sea ice decline. Differences between the models’ mean states, including the Atlantic mean surface freshwater fluxes, control the differences in AMOC stability. Our results demonstrate that the AMOC stability indicator is indeed useful for evaluating AMOC sensitivity to perturbations. Finally, we emphasize that, despite the differences in the long-term adjustment, both models simulate a multi-decadal AMOC weakening caused by Arctic sea ice decline, relevant to climate change.

scholarly journals Response of Northern Hemisphere weather and climate to Arctic sea ice decline: Resolution independence in Polar Amplification Model Intercomparison Project (PAMIP) simulations

2021 ◽  
pp. 1-39
Author(s):  
Jan Streffing ◽  
Tido Semmler ◽  
Lorenzo Zampieri ◽  
Thomas Jung
Keyword(s):  
Sea Ice ◽  
Horizontal Resolution ◽  
Arctic Sea Ice ◽  
Model Intercomparison ◽  
Polar Amplification ◽  
Sea Ice Decline ◽  
Arctic Sea ◽  
Weather And Climate ◽  
Intercomparison Project ◽  
The Impact

AbstractThe impact of Arctic sea ice decline on the weather and climate in mid-latitudes is still much debated, with observation suggesting a strong and models a much weaker link. In this study, we use the atmospheric model OpenIFS, in a set of model experiments following the protocol outlined in the Polar Amplification Model Intercomparison Project (PAMIP), to investigate whether the simulated atmospheric response to future changes in Arctic sea ice fundamentally depends on model resolution. More specifically, we increase the horizontal resolution of the model from 125km to 39km with 91 vertical levels; in a second step resolution is further increased to 16km with 137 levels in the vertical. The model does produce a response to sea ice decline with a weaker mid latitude Atlantic jet and increased blocking in the high latitude Atlantic, but no sensitivity to resolution can be detected with 100 members. Furthermore we find that the ensemble convergence toward the mean is not impacted by the model resolutions considered here.

Impact of the Atlantic Meridional Overturning Circulation (AMOC) on Arctic Surface Air Temperature and Sea Ice Variability

2011 ◽  
Vol 24 (24) ◽  
pp. 6573-6581 ◽  
Author(s):  
Salil Mahajan ◽  
Rong Zhang ◽  
Thomas L. Delworth
Keyword(s):  
Sea Ice ◽  
Surface Air Temperature ◽  
Arctic Sea Ice ◽  
Meridional Overturning Circulation ◽  
The Arctic ◽  
Sea Ice Extent ◽  
Atlantic Sector ◽  
Control Simulation ◽  
Sea Ice Decline ◽  
Arctic Sea

Abstract The simulated impact of the Atlantic meridional overturning circulation (AMOC) on the low-frequency variability of the Arctic surface air temperature (SAT) and sea ice extent is studied with a 1000-year-long segment of a control simulation of the Geophysical Fluid Dynamics Laboratory Climate Model version 2.1. The simulated AMOC variations in the control simulation are found to be significantly anticorrelated with the Arctic sea ice extent anomalies and significantly correlated with the Arctic SAT anomalies on decadal time scales in the Atlantic sector of the Arctic. The maximum anticorrelation with the Arctic sea ice extent and the maximum correlation with the Arctic SAT occur when the AMOC index leads by one year. An intensification of the AMOC is associated with a sea ice decline in the Labrador, Greenland, and Barents Seas in the control simulation, with the largest change occurring in winter. The recent declining trend in the satellite-observed sea ice extent also shows a similar pattern in the Atlantic sector of the Arctic in the winter, suggesting the possibility of a role of the AMOC in the recent Arctic sea ice decline in addition to anthropogenic greenhouse-gas-induced warming. However, in the summer, the simulated sea ice response to the AMOC in the Pacific sector of the Arctic is much weaker than the observed declining trend, indicating a stronger role for other climate forcings or variability in the recently observed summer sea ice decline in the Chukchi, Beaufort, East Siberian, and Laptev Seas.

Impact of CMIP6 biomass burning emissions on Arctic sea ice loss

2021 ◽  
Author(s):  
Patricia DeRepentigny ◽  
Alexandra Jahn ◽  
Marika Holland ◽  
John Fasullo ◽  
Jean-François Lamarque ◽  
...  
Keyword(s):  
Sea Ice ◽  
Biomass Burning ◽  
Climate Models ◽  
Arctic Sea Ice ◽  
Fire Emissions ◽  
Annual Variability ◽  
Aerosol Forcing ◽  
Sea Ice Decline ◽  
Arctic Sea ◽  
Arctic Sea Ice Loss

<p>The use of the Global Fire Emissions Database (GFED) from 1997-2014 to create the CMIP6 historical biomass burning (BB) forcing allows for a more accurate representation of BB emissions in climate models, but also results in an unrealistic increase in their inter-annual variability compared to pre- and post-GFED years, especially in the Northern Hemisphere mid-latitudes. We find that this new BB forcing affects the simulated Arctic sea ice loss in several CMIP6 models, bringing them into better agreement with the observed sea ice decline by leading to enhanced sea ice loss in the early 21<sup>st</sup> century. This suggests that BB emissions may have played a role in the acceleration of the observed early 21<sup>st</sup> century Arctic sea ice loss.</p><p>Using the Community Earth System Model version 2 (CESM2), we conduct sensitivity experiments in which we use BB emissions with a fixed annual cycle over the GFED period, to remove the inter-annual variability between 40-70°N. These experiments show that the strong acceleration in sea ice decline since the late 1990s simulated by the CESM2 is caused by enhanced Arctic warming driven by the increased variability in BB emissions over the GFED period. We also find that about half of the increase in sea ice sensitivity to CO<sub>2</sub> and global mean surface temperature in the CESM2 compared to its CMIP5 counterpart, the CESM1, can be attributed to the change in BB emissions from CMIP5 to CMIP6, which suggests that the previously found improvement in sea ice sensitivity in CMIP6 models may in part be due to this new BB forcing and not only to changes in model physics. Overall, the results from this analysis highlight the influence of mid-latitude BB emissions on Arctic sea ice and provide new insights into the potential of a forced contribution to the observed accelerated early 21<sup>st</sup> century Arctic sea ice loss. Furthermore, this work highlights the importance of avoiding temporal discontinuities in prescribed aerosol forcing datasets as well as the need to better understand inter-model contrasts within the CMIP6 archive related to sensitivity to BB emissions.</p>

scholarly journals Persistent Freshening of the Arctic Ocean and Changes in the North Atlantic Salinity Caused by Arctic Sea Ice Decline

2021 ◽  
Author(s):  
Hui Li ◽  
Alexey Fedorov
Keyword(s):  
Sea Ice ◽  
Arctic Ocean ◽  
North Atlantic ◽  
Arctic Sea Ice ◽  
Meridional Overturning Circulation ◽  
The Arctic ◽  
Global Ocean ◽  
Ice Melting ◽  
Sea Ice Decline ◽  
Arctic Sea

Abstract Arctic sea ice has been declining over past several decades with the largest ice loss occurring in summer. This implies a strengthening of the sea ice seasonal cycle. Here, we examine global ocean salinity response to such changes of Arctic sea ice using simulations wherein we impose a radiative heat imbalance at the sea ice surface, inducing a sea ice decline comparable to the observed. The imposed perturbation leads to enhanced seasonal melting and a rapid retreat of Arctic sea ice within the first 5-10 years. We then observe a gradual freshening of the upper Arctic ocean that continues for about a century. The freshening is most pronounced within the central Arctic, including the Beaufort gyre, and is attributed to excess surface freshwater associated with the stronger seasonal sea ice melting, as well as a greater upper-ocean freshwater storage due to changes in ocean circulation. The freshening of the Nordic Seas can also occur via a distillation-like process in which denser saline waters with increased salinity are exported to the subtropical/tropical North Atlantic by meridional overturning circulation. Thus, enhanced seasonal sea ice melting in a warmer climate can lead to a persistent Arctic freshening with large impacts on the global salinity distribution.

scholarly journals Attribution of Arctic Sea Ice Decline from 1953 to 2012 to Influences from Natural, Greenhouse Gas, and Anthropogenic Aerosol Forcing

2018 ◽  
Vol 31 (19) ◽  
pp. 7771-7787 ◽  
Author(s):  
B. L. Mueller ◽  
N. P. Gillett ◽  
A. H. Monahan ◽  
F. W. Zwiers
Keyword(s):  
Sea Ice ◽  
Greenhouse Gas ◽  
Climate Models ◽  
Arctic Sea Ice ◽  
Sea Ice Extent ◽  
Anthropogenic Forcing ◽  
Detection And Attribution ◽  
Sea Ice Decline ◽  
Arctic Sea ◽  
Arctic Sea Ice Extent

The paper presents results from a climate change detection and attribution study on the decline of Arctic sea ice extent in September for the 1953–2012 period. For this period three independently derived observational datasets and simulations from multiple climate models are available to attribute observed changes in the sea ice extent to known climate forcings. Here we direct our attention to the combined cooling effect from other anthropogenic forcing agents (mainly aerosols), which has potentially masked a fraction of greenhouse gas–induced Arctic sea ice decline. The presented detection and attribution framework consists of a regression model, namely, regularized optimal fingerprinting, where observations are regressed onto model-simulated climate response patterns (i.e., fingerprints). We show that fingerprints from greenhouse gas, natural, and other anthropogenic forcings are detected in the three observed records of Arctic sea ice extent. Beyond that, our findings indicate that for the 1953–2012 period roughly 23% of the greenhouse gas–induced negative sea ice trend has been offset by a weak positive sea ice trend attributable to other anthropogenic forcing. We show that our detection and attribution results remain robust in the presence of emerging nonstationary internal climate variability acting upon sea ice using a perfect model experiment and data from two large ensembles of climate simulations.

scholarly journals Observation-based selection of climate models projects Arctic ice-free summers around 2035

2021 ◽  
Vol 2 (1) ◽  
Author(s):  
David Docquier ◽  
Torben Koenigk
Keyword(s):  
Model Selection ◽  
Sea Ice ◽  
Climate Models ◽  
Global Climate ◽  
Coupled Model ◽  
Arctic Sea Ice ◽  
Global Climate Models ◽  
The Arctic ◽  
Arctic Sea ◽  
Area And Volume

AbstractArctic sea ice has been retreating at an accelerating pace over the past decades. Model projections show that the Arctic Ocean could be almost ice free in summer by the middle of this century. However, the uncertainties related to these projections are relatively large. Here we use 33 global climate models from the Coupled Model Intercomparison Project 6 (CMIP6) and select models that best capture the observed Arctic sea-ice area and volume and northward ocean heat transport to refine model projections of Arctic sea ice. This model selection leads to lower Arctic sea-ice area and volume relative to the multi-model mean without model selection and summer ice-free conditions could occur as early as around 2035. These results highlight a potential underestimation of future Arctic sea-ice loss when including all CMIP6 models.

scholarly journals What Do Global Climate Models Tell Us about Future Arctic Sea Ice Coverage Changes?

Climate ◽  
2020 ◽  
Vol 8 (1) ◽  
pp. 15 ◽  
Author(s):  
Ge Peng ◽  
Jessica L. Matthews ◽  
Muyin Wang ◽  
Russell Vose ◽  
Liqiang Sun
Keyword(s):  
Sea Ice ◽  
Climate Models ◽  
Climate Adaptation ◽  
Global Climate ◽  
Arctic Sea Ice ◽  
Global Climate Models ◽  
Climate Projections ◽  
Emission Scenarios ◽  
Ice Coverage ◽  
Arctic Sea

The prospect of an ice-free Arctic in our near future due to the rapid and accelerated Arctic sea ice decline has brought about the urgent need for reliable projections of the first ice-free Arctic summer year (FIASY). Together with up-to-date observations and characterizations of Arctic ice state, they are essential to business strategic planning, climate adaptation, and risk mitigation. In this study, the monthly Arctic sea ice extents from 12 global climate models are utilized to obtain projected FIASYs and their dependency on different emission scenarios, as well as to examine the nature of the ice retreat projections. The average value of model-projected FIASYs is 2054/2042, with a spread of 74/42 years for the medium/high emission scenarios, respectively. The earliest FIASY is projected to occur in year 2023, which may not be realistic, for both scenarios. The sensitivity of individual climate models to scenarios in projecting FIASYs is very model-dependent. The nature of model-projected Arctic sea ice coverage changes is shown to be primarily linear. FIASY values predicted by six commonly used statistical models that were curve-fitted with the first 30 years of climate projections (2006–2035), on other hand, show a preferred range of 2030–2040, with a distinct peak at 2034 for both scenarios, which is more comparable with those from previous studies.

scholarly journals Seasonal to interannual Arctic sea ice predictability in current global climate models

2014 ◽  
Vol 41 (3) ◽  
pp. 1035-1043 ◽  
Author(s):  
S. Tietsche ◽  
J. J. Day ◽  
V. Guemas ◽  
W. J. Hurlin ◽  
S. P. E. Keeley ◽  
...  
Keyword(s):  
Sea Ice ◽  
Climate Models ◽  
Global Climate ◽  
Arctic Sea Ice ◽  
Global Climate Models ◽  
Arctic Sea
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