scholarly journals Forced Patterns of Sea Level Rise in the Community Earth System Model Large Ensemble From 1920 to 2100

2020 ◽  
Vol 125 (6) ◽  
Author(s):  
John T. Fasullo ◽  
Peter R. Gent ◽  
R. S. Nerem
Keyword(s):  
Sea Level Rise ◽  
Sea Level ◽  
Earth System Model ◽  
System Model ◽  
Earth System ◽  
Large Ensemble ◽  
Community Earth System Model

scholarly journals Altimeter-era emergence of the patterns of forced sea-level rise in climate models and implications for the future

2018 ◽  
Vol 115 (51) ◽  
pp. 12944-12949 ◽  
Author(s):  
John T. Fasullo ◽  
R. Steven Nerem
Keyword(s):  
Sea Level Rise ◽  
Sea Level ◽  
Climate Models ◽  
Internal Variability ◽  
Forced Response ◽  
Earth System Model ◽  
System Model ◽  
Earth System ◽  
Community Earth System Model

The satellite altimeter record has provided an unprecedented database for understanding sea-level rise and has recently reached a major milestone at 25 years in length. A challenge now exists in understanding its broader significance and its consequences for sea-level rise in the coming decades and beyond. A key question is whether the pattern of altimeter-era change is representative of longer-term trends driven by anthropogenic forcing. In this work, two multimember climate ensembles, the Community Earth System Model (CESM) and the Earth System Model Version 2M (ESM2M), are used to estimate patterns of forced change [also known as the forced response (FR)] and their magnitudes relative to internal variability. It is found that the spatial patterns of 1993–2018 trends in the ensembles correlate significantly with the contemporaneous FRs (0.55 ± 0.10 in the CESM and 0.61 ± 0.09 in the ESM2M) and the 1950–2100 FRs (0.43 ± 0.10 in the CESM and 0.51 ± 0.11 in the ESM2M). Unforced runs for each model show such correlations to be extremely unlikely to have arisen by chance, indicating an emergence of both the altimeter-era and long-term FRs and suggesting a similar emergence in nature. Projected patterns of the FR over the coming decades resemble those simulated during the altimeter era, suggesting a continuation of the forced pattern of change in nature in the coming decades. Notably, elevated rates of rise are projected to continue in regions that are susceptible to tropical cyclones, exacerbating associated impacts in a warming climate.

scholarly journals Implementation and Initial Evaluation of the Glimmer Community Ice Sheet Model in the Community Earth System Model

2013 ◽  
Vol 26 (19) ◽  
pp. 7352-7371 ◽  
Author(s):  
William H. Lipscomb ◽  
Jeremy G. Fyke ◽  
Miren Vizcaíno ◽  
William J. Sacks ◽  
Jon Wolfe ◽  
...  
Keyword(s):  
Sea Level Rise ◽  
Sea Level ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Earth System Model ◽  
System Model ◽  
Thermomechanical Coupling ◽  
Quasi Equilibrium ◽  
Earth System ◽  
Community Earth System Model

Abstract The Glimmer Community Ice Sheet Model (Glimmer-CISM) has been implemented in the Community Earth System Model (CESM). Glimmer-CISM is forced by a surface mass balance (SMB) computed in multiple elevation classes in the CESM land model and downscaled to the ice sheet grid. Ice sheet evolution is governed by the shallow-ice approximation with thermomechanical coupling and basal sliding. This paper describes and evaluates the initial model implementation for the Greenland Ice Sheet (GIS). The ice sheet model was spun up using the SMB from a coupled CESM simulation with preindustrial forcing. The model's sensitivity to three key ice sheet parameters was explored by running an ensemble of 100 GIS simulations to quasi equilibrium and ranking each simulation based on multiple diagnostics. With reasonable parameter choices, the steady-state GIS geometry is broadly consistent with observations. The simulated ice sheet is too thick and extensive, however, in some marginal regions where the SMB is anomalously positive. The top-ranking simulations were continued using surface forcing from CESM simulations of the twentieth century (1850–2005) and twenty-first century (2005–2100, with RCP8.5 forcing). In these simulations the GIS loses mass, with a resulting global-mean sea level rise of 16 mm during 1850–2005 and 60 mm during 2005–2100. This mass loss is caused mainly by increased ablation near the ice sheet margin, offset by reduced ice discharge to the ocean. Projected sea level rise is sensitive to the initial geometry, showing the importance of realistic geometry in the spun-up ice sheet.

The Community Earth System Model (CESM) Large Ensemble Project: A Community Resource for Studying Climate Change in the Presence of Internal Climate Variability

2015 ◽  
Vol 96 (8) ◽  
pp. 1333-1349 ◽  
Author(s):  
J. E. Kay ◽  
C. Deser ◽  
A. Phillips ◽  
A. Mai ◽  
C. Hannay ◽  
...  
Keyword(s):  
Climate Change ◽  
Climate Variability ◽  
Model Error ◽  
Earth System Model ◽  
First Century ◽  
System Model ◽  
Earth System ◽  
Large Ensemble ◽  
Internal Climate Variability ◽  
Community Earth System Model

Abstract While internal climate variability is known to affect climate projections, its influence is often underappreciated and confused with model error. Why? In general, modeling centers contribute a small number of realizations to international climate model assessments [e.g., phase 5 of the Coupled Model Intercomparison Project (CMIP5)]. As a result, model error and internal climate variability are difficult, and at times impossible, to disentangle. In response, the Community Earth System Model (CESM) community designed the CESM Large Ensemble (CESM-LE) with the explicit goal of enabling assessment of climate change in the presence of internal climate variability. All CESM-LE simulations use a single CMIP5 model (CESM with the Community Atmosphere Model, version 5). The core simulations replay the twenty to twenty-first century (1920–2100) 30 times under historical and representative concentration pathway 8.5 external forcing with small initial condition differences. Two companion 1000+-yr-long preindustrial control simulations (fully coupled, prognostic atmosphere and land only) allow assessment of internal climate variability in the absence of climate change. Comprehensive outputs, including many daily fields, are available as single-variable time series on the Earth System Grid for anyone to use. Early results demonstrate the substantial influence of internal climate variability on twentieth- to twenty-first-century climate trajectories. Global warming hiatus decades occur, similar to those recently observed. Internal climate variability alone can produce projection spread comparable to that in CMIP5. Scientists and stakeholders can use CESM-LE outputs to help interpret the observational record, to understand projection spread and to plan for a range of possible futures influenced by both internal climate variability and forced climate change.

scholarly journals Predicting Near-Term Changes in the Earth System: A Large Ensemble of Initialized Decadal Prediction Simulations Using the Community Earth System Model

2018 ◽  
Vol 99 (9) ◽  
pp. 1867-1886 ◽  
Author(s):  
S. G. Yeager ◽  
G. Danabasoglu ◽  
N. A. Rosenbloom ◽  
W. Strand ◽  
S. C. Bates ◽  
...  
Keyword(s):  
Earth System Model ◽  
Prediction Skill ◽  
System Model ◽  
Decadal Prediction ◽  
Earth System ◽  
Large Ensemble ◽  
Past Climate ◽  
Radiative Forcings ◽  
Community Earth System Model ◽  
Near Term

AbstractThe objective of near-term climate prediction is to improve our fore-knowledge, from years to a decade or more in advance, of impactful climate changes that can in general be attributed to a combination of internal and externally forced variability. Predictions initialized using observations of past climate states are tested by comparing their ability to reproduce past climate evolution with that of uninitialized simulations in which the same radiative forcings are applied. A new set of decadal prediction (DP) simulations has recently been completed using the Community Earth System Model (CESM) and is now available to the community. This new large-ensemble (LE) set (CESM-DPLE) is composed of historical simulations that are integrated forward for 10 years following initialization on 1 November of each year between 1954 and 2015. CESM-DPLE represents the “initialized” counterpart to the widely studied CESM Large Ensemble (CESM-LE); both simulation sets have 40-member ensembles, and they use identical model code and radiative forcings. Comparing CESM-DPLE to CESM-LE highlights the impacts of initialization on prediction skill and indicates that robust assessment and interpretation of DP skill may require much larger ensembles than current protocols recommend. CESM-DPLE exhibits significant and potentially useful prediction skill for a wide range of fields, regions, and time scales, and it shows widespread improvement over simpler benchmark forecasts as well as over a previous initialized system that was submitted to phase 5 of the Coupled Model Intercomparison Project (CMIP5). The new DP system offers new capabilities that will be of interest to a broad community pursuing Earth system prediction research.

scholarly journals Low-Frequency North Atlantic Climate Variability in the Community Earth System Model Large Ensemble

2018 ◽  
Vol 31 (2) ◽  
pp. 787-813 ◽  
Author(s):  
Who M. Kim ◽  
Stephen Yeager ◽  
Ping Chang ◽  
Gokhan Danabasoglu
Keyword(s):  
Boundary Conditions ◽  
Time Scales ◽  
North Atlantic ◽  
Low Frequency ◽  
Earth System Model ◽  
System Model ◽  
Earth System ◽  
Large Ensemble ◽  
Low Frequency Variability ◽  
Community Earth System Model

There is observational and modeling evidence that low-frequency variability in the North Atlantic has significant implications for the global climate, particularly for the climate of the Northern Hemisphere. This study explores the representation of low-frequency variability in the Atlantic region in historical large ensemble and preindustrial control simulations performed with the Community Earth System Model (CESM). Compared to available observational estimates, it is found that the simulated variability in Atlantic meridional overturning circulation (AMOC), North Atlantic sea surface temperature (NASST), and Sahel rainfall is underestimated on multidecadal time scales but comparable on interannual to decadal time scales. The weak multidecadal North Atlantic variability appears to be closely related to weaker-than-observed multidecadal variations in the simulated North Atlantic Oscillation (NAO), as the AMOC and consequent NASST variability is impacted, to a great degree, by the NAO. Possible reasons for this weak multidecadal NAO variability are explored with reference to solutions from two atmosphere-only simulations with different lower boundary conditions and vertical resolution. Both simulations consistently reveal weaker-than-observed multidecadal NAO variability despite more realistic boundary conditions and better resolved dynamics than coupled simulations. The authors thus conjecture that the weak multidecadal NAO variability in CESM is likely due to deficiencies in air–sea coupling, resulting from shortcomings in the atmospheric model or coupling details.

CO2 increase experiments using the Community Earth System Model (CESM): Relationship to climate sensitivity and comparison of CESM1 to CESM2

2020 ◽  
Author(s):  
Julio T. Bacmeister ◽  
Cecile Hannay ◽  
Brian Medeiros ◽  
Andrew Gettelman ◽  
Richard Neale ◽  
...  
Keyword(s):  
Climate Sensitivity ◽  
Earth System Model ◽  
System Model ◽  
Earth System ◽  
Community Earth System Model
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