Simulation of Present-Day and Future Permafrost and Seasonally Frozen Ground Conditions in CCSM4

2012 ◽  
Vol 25 (7) ◽  
pp. 2207-2225 ◽  
Author(s):  
David M. Lawrence ◽  
Andrew G. Slater ◽  
Sean C. Swenson
Keyword(s):  
First Century ◽  
Arctic Climate ◽  
Active Layer Thickness ◽  
Permafrost Degradation ◽  
Frozen Ground ◽  
Climate System Model ◽  
Near Surface ◽  
Community Land Model ◽  
Model Version ◽  
Twenty First Century

Abstract The representation of permafrost and seasonally frozen ground and their projected twenty-first century trends is assessed in the Community Climate System Model, version 4 (CCSM4) and the Community Land Model version 4 (CLM4). The combined impact of advances in CLM and a better Arctic climate simulation, especially for air temperature, improve the permafrost simulation in CCSM4 compared to CCSM3. Present-day continuous plus discontinuous permafrost extent is comparable to that observed [12.5 × 106 versus (11.8–14.6) × 106 km2], but active-layer thickness (ALT) is generally too thick and deep ground (>15 m) temperatures are too warm in CCSM4. Present-day seasonally frozen ground area is well simulated (47.5 × 106 versus 48.1 × 106 km2). ALT and deep ground temperatures are much better simulated in offline CLM4 (i.e., forced with observed climate), which indicates that the remaining climate biases, particularly excessive high-latitude snowfall biases, degrade the CCSM4 permafrost simulation. Near-surface permafrost (NSP) and seasonally frozen ground (SFG) area are projected to decline substantially during the twenty-first century [representative concentration projections (RCPs); RCP8.5: NSP by 9.0 × 106 km2, 72%, SFG by 7.1 × 106, 15%; RCP2.6: NSP by 4.1 × 106, 33%, SFG by 2.1 × 106, 4%]. The permafrost degradation rate is slower (2000–50) than in CCSM3 by ~35% because of the improved soil physics. Under the low RCP2.6 emissions pathway, permafrost state stabilizes by 2100, suggesting that permafrost related feedbacks could be minimized if greenhouse emissions could be reduced. The trajectory of permafrost degradation is affected by CCSM4 climate biases. In simulations with this climate bias ameliorated, permafrost degradation in RCP8.5 is lower by ~29%. Further reductions of Arctic climate biases will increase the reliability of permafrost projections and feedback studies in earth system models.

Twenty-First-Century Arctic Climate Change in CCSM4

2012 ◽  
Vol 25 (8) ◽  
pp. 2696-2710 ◽  
Author(s):  
Stephen J. Vavrus ◽  
Marika M. Holland ◽  
Alexandra Jahn ◽  
David A. Bailey ◽  
Benjamin A. Blazey
Keyword(s):  
Climate Change ◽  
Arctic Ocean ◽  
Radiative Forcing ◽  
First Century ◽  
Arctic Climate ◽  
The Arctic ◽  
Climate System Model ◽  
Temperature Isotherm ◽  
Twenty First Century ◽  
Arctic Climate Change

Abstract The authors summarize the twenty-first-century Arctic climate simulated by NCAR’s Community Climate System Model, version 4 (CCSM4). Under a strong radiative forcing scenario, the model simulates a much warmer, wetter, cloudier, and stormier Arctic climate with considerably less sea ice and a fresher Arctic Ocean. The high correlation among the variables composing these changes—temperature, precipitation, cloudiness, sea level pressure (SLP), and ice concentration—suggests that their close coupling collectively represents a fingerprint of Arctic climate change. Although the projected changes in CCSM4 are generally consistent with those in other GCMs, several noteworthy features are identified. Despite more global warming in CCSM4, Arctic changes are generally less than under comparable greenhouse forcing in CCSM3, as represented by Arctic amplification (16% weaker) and the date of a seasonally ice-free Arctic Ocean (20 years later). Autumn is the season of the most pronounced Arctic climate change among all the primary variables. The changes are very similar across the five ensemble members, although SLP displays the largest internal variability. The SLP response exhibits a significant trend toward stronger extreme Arctic cyclones, implying greater wave activity that would promote coastal erosion. Based on a commonly used definition of the Arctic (the area encompassing the 10°C July air temperature isotherm), the region shrinks by about 40% during the twenty-first century, in conjunction with a nearly 10-K warming trend poleward of 70°N. Despite this pronounced long-term warming, CCSM4 simulates a hiatus in the secular Arctic climate trends during a decade-long stretch in the 2040s and to a lesser extent in the 2090s. These pauses occur despite averaging over five ensemble members and are remarkable because they happen under the most extreme greenhouse-forcing scenario and in the most climatically sensitive region of the world.

scholarly journals Climate System Response to External Forcings and Climate Change Projections in CCSM4

2012 ◽  
Vol 25 (11) ◽  
pp. 3661-3683 ◽  
Author(s):  
Gerald A. Meehl ◽  
Warren M. Washington ◽  
Julie M. Arblaster ◽  
Aixue Hu ◽  
Haiyan Teng ◽  
...  
Keyword(s):  
Twentieth Century ◽  
Sea Ice ◽  
Meridional Overturning Circulation ◽  
Climate System ◽  
First Century ◽  
The Arctic ◽  
System Response ◽  
Transient Climate Response ◽  
Climate System Model ◽  
Twenty First Century

Results are presented from experiments performed with the Community Climate System Model, version 4 (CCSM4) for the Coupled Model Intercomparison Project phase 5 (CMIP5). These include multiple ensemble members of twentieth-century climate with anthropogenic and natural forcings as well as single-forcing runs, sensitivity experiments with sulfate aerosol forcing, twenty-first-century representative concentration pathway (RCP) mitigation scenarios, and extensions for those scenarios beyond 2100–2300. Equilibrium climate sensitivity of CCSM4 is 3.20°C, and the transient climate response is 1.73°C. Global surface temperatures averaged for the last 20 years of the twenty-first century compared to the 1986–2005 reference period for six-member ensembles from CCSM4 are +0.85°, +1.64°, +2.09°, and +3.53°C for RCP2.6, RCP4.5, RCP6.0, and RCP8.5, respectively. The ocean meridional overturning circulation (MOC) in the Atlantic, which weakens during the twentieth century in the model, nearly recovers to early twentieth-century values in RCP2.6, partially recovers in RCP4.5 and RCP6, and does not recover by 2100 in RCP8.5. Heat wave intensity is projected to increase almost everywhere in CCSM4 in a future warmer climate, with the magnitude of the increase proportional to the forcing. Precipitation intensity is also projected to increase, with dry days increasing in most subtropical areas. For future climate, there is almost no summer sea ice left in the Arctic in the high RCP8.5 scenario by 2100, but in the low RCP2.6 scenario there is substantial sea ice remaining in summer at the end of the century.

scholarly journals Probabilistic Projections of Climate Change over China under the SRES A1B Scenario Using 28 AOGCMs

2011 ◽  
Vol 24 (17) ◽  
pp. 4741-4756 ◽  
Author(s):  
Weilin Chen ◽  
Zhihong Jiang ◽  
Laurent Li
Keyword(s):  
Climate Change ◽  
Interannual Variability ◽  
General Circulation ◽  
Regional Scale ◽  
First Century ◽  
Climate System Model ◽  
Huai River ◽  
Twenty First Century ◽  
The Impact ◽  
A1b Scenario

Probabilistic projection of climate change consists of formulating the climate change information in a probabilistic manner at either global or regional scale. This can produce useful results for studies of the impact of climate change impact and change mitigation. In the present study, a simple yet effective approach is proposed with the purpose of producing probabilistic results of climate change over China for the middle and end of the twenty-first century under the Special Report on Emissions Scenarios A1B (SRES A1B) emission scenario. Data from 28 coupled atmosphere–ocean general circulation models (AOGCMs) are used. The methodology consists of ranking the 28 models, based on their ability to simulate climate over China in terms of two model evaluation metrics. Different weights were then given to the models according to their performances in present-day climate. Results of the evaluation for the current climate show that five models that have relatively higher resolutions—namely, the Istituto Nazionale di Geofisica e Vulcanologia ECHAM4 (INGV ECHAM4), the third climate configuration of the Met Office Unified Model (UKMO HadCM3), the CSIRO Mark version 3.5 (Mk3.5), the NCAR Community Climate System Model, version 3 (CCSM3), and the Model for Interdisciplinary Research on Climate 3.2, high-resolution version [MIROC3.2 (hires)]—perform better than others over China. Their corresponding weights (normalized to 1) are 0.289, 0.096, 0.058, 0.048, and 0.044, respectively. Under the A1B scenario, surface air temperature is projected to increase significantly for both the middle and end of the twenty-first century, with larger magnitude over the north and in winter. There are also significant increases in rainfall in the twenty-first century under the A1B scenario, especially for the period 2070–99. As far as the interannual variability is concerned, the most striking feature is that there are high probabilities for the future intensification of interannual variability of precipitation over most of China in both winter and summer. For instance, over the Yangtze–Huai River basin (28°–35°N, 105°–120°E), there is a 60% probability of increased interannual standard deviation of precipitation by 20% in summer, which is much higher than that of the mean precipitation. In general there are small differences between weighted and unweighted projections, but the uncertainties in the projected changes are reduced to some extent after weighting.

Climate Change Projections in CESM1(CAM5) Compared to CCSM4

2013 ◽  
Vol 26 (17) ◽  
pp. 6287-6308 ◽  
Author(s):  
Gerald A. Meehl ◽  
Warren M. Washington ◽  
Julie M. Arblaster ◽  
Aixue Hu ◽  
Haiyan Teng ◽  
...  
Keyword(s):  
Climate Change ◽  
Meridional Overturning Circulation ◽  
Climate System ◽  
First Century ◽  
System Model ◽  
Future Climate Change ◽  
System Response ◽  
Climate Change Projections ◽  
Model Version ◽  
Twenty First Century

Abstract Future climate change projections for phase 5 of the Coupled Model Intercomparison Project (CMIP5) are presented for the Community Earth System Model version 1 that includes the Community Atmospheric Model version 5 [CESM1(CAM5)]. These results are compared to the Community Climate System Model, version 4 (CCSM4) and include simulations using the representative concentration pathway (RCP) mitigation scenarios, and extensions for those scenarios beyond 2100 to 2300. Equilibrium climate sensitivity of CESM1(CAM5) is 4.10°C, which is higher than the CCSM4 value of 3.20°C. The transient climate response is 2.33°C, compared to the CCSM4 value of 1.73°C. Thus, even though CESM1(CAM5) includes both the direct and indirect effects of aerosols (CCSM4 had only the direct effect), the overall climate system response including forcing and feedbacks is greater in CESM1(CAM5) compared to CCSM4. The Atlantic Ocean meridional overturning circulation (AMOC) in CESM1(CAM5) weakens considerably in the twenty-first century in all the RCP scenarios, and recovers more slowly in the lower forcing scenarios. The total aerosol optical depth (AOD) changes from ~0.12 in 2006 to ~0.10 in 2100, compared to a preindustrial 1850 value of 0.08, so there is less negative forcing (a net positive forcing) from that source during the twenty-first century. Consequently, the change from 2006 to 2100 in aerosol direct forcing in CESM1(CAM5) contributes to greater twenty-first century warming relative to CCSM4. There is greater Arctic warming and sea ice loss in CESM1(CAM5), with an ice-free summer Arctic occurring by about 2060 in RCP8.5 (2040s in September) as opposed to about 2100 in CCSM4 (2060s in September).

Attribution of Projected Changes in Atmospheric Moisture Transport in the Arctic: A Self-Organizing Map Perspective

2009 ◽  
Vol 22 (15) ◽  
pp. 4135-4153 ◽  
Author(s):  
Natasa Skific ◽  
Jennifer A. Francis ◽  
John J. Cassano
Keyword(s):  
Twentieth Century ◽  
Moisture Transport ◽  
First Century ◽  
The Arctic ◽  
Self Organizing Map ◽  
Total Change ◽  
Intergovernmental Panel ◽  
Climate System Model ◽  
Twenty First Century ◽  
Self Organizing

Abstract Meridonal moisture transport into the Arctic derived from one simulation of the National Center for Atmospheric Research Community Climate System Model (CCSM3), spanning the periods of 1960–99, 2010–30, and 2070–89, is analyzed. The twenty-first-century simulation incorporates the Intergovernmental Panel on Climate Change (IPCC) Special Report on Emission Scenarios (SRES) A2 scenario for CO2 and sulfate emissions. Modeled and observed [from the 40-yr ECMWF Re-Analysis (ERA-40)] sea level pressure (SLP) fields are classified using a neural network technique called self-organizing maps to distill a set of characteristic atmospheric circulation patterns over the region north of 60°N. Model performance is validated for the twentieth century by comparing the frequencies of occurrence of particular circulation regimes in the model to those from the ERA-40. The model successfully captures dominant SLP patterns, but differs from observations in the frequency with which certain patterns occur. The model’s twentieth-century vertical mean moisture transport profile across 70°N compares well in terms of structure but exceeds the observations by about 12% overall. By relating moisture transport to a particular circulation regime, future changes in moisture transport across 70°N are assessed and attributed to changes in frequency with which the atmosphere resides in particular SLP patterns and/or to other factors, such as changes in the meridional moisture gradient. By the late twenty-first century, the transport is projected to increase by about 21% in this model realization, with the largest contribution (32%) to the total change occurring in summer. Only about one-quarter of the annual increase is due to changes in pattern occupancy, suggesting that the majority is related to mainly thermodynamic factors. A larger poleward moisture transport likely constitutes a positive feedback on the system through related increases in latent heat release and the emission of longwave radiation to the surface.

scholarly journals Will There Be a Significant Change to El Niño in the Twenty-First Century?

2012 ◽  
Vol 25 (6) ◽  
pp. 2129-2145 ◽  
Author(s):  
Samantha Stevenson ◽  
Baylor Fox-Kemper ◽  
Markus Jochum ◽  
Richard Neale ◽  
Clara Deser ◽  
...  
Keyword(s):  
Climate Change ◽  
El Niño ◽  
El Nino ◽  
Southern Oscillation ◽  
Ocean Dynamics ◽  
First Century ◽  
Climate System Model ◽  
Enso Variability ◽  
Tropical Variability ◽  
Twenty First Century

Abstract The El Niño–Southern Oscillation (ENSO) response to anthropogenic climate change is assessed in the following 1° nominal resolution Community Climate System Model, version 4 (CCSM4) Coupled Model Intercomparison Project phase 5 (CMIP5) simulations: twentieth-century ensemble, preindustrial control, twenty-first-century projections, and stabilized 2100–2300 “extension runs.” ENSO variability weakens slightly with CO2; however, various significance tests reveal that changes are insignificant at all but the highest CO2 levels. Comparison with the 1850 control simulation suggests that ENSO changes may become significant on centennial time scales; the lack of signal in the twentieth- versus twenty-first-century ensembles is due to their limited duration. Changes to the mean state are consistent with previous studies: a weakening of the subtropical wind stress curl, an eastward shift of the tropical convective cells, a reduction in the zonal SST gradient, and an increase in vertical thermal stratification take place as CO2 increases. The extratropical thermocline deepens throughout the twenty-first century, with the tropical thermocline changing slowly in response. The adjustment time scale is set by the relevant ocean dynamics, and the delay in its effect on ENSO variability is not diminished by increasing ensemble size. The CCSM4 results imply that twenty-first-century simulations may simply be too short for identification of significant tropical variability response to climate change. An examination of atmospheric teleconnections, in contrast, shows that the remote influences of ENSO do respond rapidly to climate change in some regions, particularly during boreal winter. This suggests that changes to ENSO impacts may take place well before changes to oceanic tropical variability itself become significant.

scholarly journals Uncertainties in Future Projections of Summer Droughts and Heat Waves over the Contiguous United States

2017 ◽  
Vol 30 (16) ◽  
pp. 6225-6246 ◽  
Author(s):  
Julio E. Herrera-Estrada ◽  
Justin Sheffield
Keyword(s):  
United States ◽  
Heat Waves ◽  
The United States ◽  
First Century ◽  
Climate Mitigation ◽  
Large Uncertainty ◽  
Near Surface ◽  
Future Projections ◽  
Twenty First Century ◽  
Atmospheric Coupling

Droughts and heat waves have important impacts on multiple sectors including water resources, agriculture, electricity generation, and public health, so it is important to understand how they will be affected by climate change. However, there is large uncertainty in the projected changes of these extreme events from climate models. In this study, historical biases in models are compared against their future projections to understand and attempt to constrain these uncertainties. Biases in precipitation, near-surface air temperature, evapotranspiration, and a land–atmospheric coupling metric are calculated for 24 models from phase 5 of the Coupled Model Intercomparison Project (CMIP5) against 2 models from phase 2 of the North American Land Data Assimilation System (NLDAS-2) as reference for 1979–2005. These biases are highly correlated across variables, with some models being hotter and drier and others wetter and cooler. Models that overestimate summer precipitation project larger increases in precipitation, evapotranspiration, and land–atmospheric coupling over important agricultural regions by the end of the twenty-first century (2070–99) under RCP8.5, although the percentage variance explained is low. Changes in the characteristics of droughts and heat waves are calculated and linked to historical biases in precipitation and temperature. A method to constrain uncertainty by ranking models based on historical performance is discussed but the rankings differ widely depending on the variable considered. Despite the large uncertainty that remains in the magnitude of the changes, there is consensus among models that droughts and heat waves will increase in multiple regions in the United States by the end of the twenty-first century unless climate mitigation actions are taken.

scholarly journals The changing nature of hydroclimatic risks across South Africa

2021 ◽  
Vol 168 (3-4) ◽  
Author(s):  
Adam Schlosser ◽  
Andrei Sokolov ◽  
Ken Strzepek ◽  
Tim Thomas ◽  
Xiang Gao ◽  
...  
Keyword(s):  
South Africa ◽  
Air Temperature ◽  
Climate Models ◽  
Global Climate ◽  
Coupled Model ◽  
Surface Air Temperature ◽  
First Century ◽  
Near Surface ◽  
Climate Targets ◽  
Twenty First Century

AbstractWe present results from large ensembles of projected twenty-first century changes in seasonal precipitation and near-surface air temperature for the nation of South Africa. These ensembles are a result of combining Monte Carlo projections from a human-Earth system model of intermediate complexity with pattern-scaled responses from climate models of the Coupled Model Intercomparison Project Phase 5 (CMIP5). These future ensemble scenarios consider a range of global actions to abate emissions through the twenty-first century. We evaluate distributions of surface-air temperature and precipitation change over three sub-national regions: western, central, and eastern South Africa. In all regions, we find that without any emissions or climate targets in place, there is a greater than 50% likelihood that mid-century temperatures will increase threefold over the current climate’s two-standard deviation range of variability. However, scenarios that consider more aggressive climate targets all but eliminate the risk of these salient temperature increases. A preponderance of risk toward decreased precipitation (3 to 4 times higher than increased) exists for western and central South Africa. Strong climate targets abate evolving regional hydroclimatic risks. Under a target to limit global climate warming to 1.5 °C by 2100, the risk of precipitation changes within South Africa toward the end of this century (2065–2074) is commensurate to the risk during the 2030s without any global climate target. Thus, these regional hydroclimate risks over South Africa could be delayed by 30 years and, in doing so, provide invaluable lead-time for national efforts to prepare, fortify, and/or adapt.

scholarly journals Deglacial permafrost carbon dynamics in MPI-ESM

2018 ◽  
Author(s):  
Thomas Schneider von Deimling ◽  
Thomas Kleinen ◽  
Gustaf Hugelius ◽  
Christian Knoblauch ◽  
Christian Beer ◽  
...  
Keyword(s):  
Boundary Conditions ◽  
Soil Carbon ◽  
Active Layer ◽  
Carbon Accumulation ◽  
Surface Model ◽  
Model Parameters ◽  
Moderate Increase ◽  
Permafrost Degradation ◽  
Frozen Ground ◽  
Near Surface

Abstract. We have developed a new module to calculate soil organic carbon (SOC) accumulation in perennially frozen ground in the land surface model JSBACH. Running this offline version of MPI-ESM we have modelled permafrost carbon accumulation and release from the Last Glacial Maximum (LGM) to the Pre-industrial (PI). Our simulated near-surface PI permafrost extent of 16.9 Mio km2 is close to observational evidence. Glacial boundary conditions, especially ice sheet coverage, result in profoundly different spatial patterns of glacial permafrost extent. Deglacial warming leads to large-scale changes in soil temperatures, manifested in permafrost disappearance in southerly regions, and permafrost aggregation in formerly glaciated grid cells. In contrast to the large spatial shift in simulated permafrost occurrence, we infer an only moderate increase of total LGM permafrost area (18.3 Mio km2) – together with pronounced changes in the depth of seasonal thaw. Reconstructions suggest a larger spread of glacial permafrost towards more southerly regions, but with a highly uncertain extent of non-continuous permafrost. Compared to a control simulation without describing the transport of SOC into perennially frozen ground, the implementation of our newly developed module for simulating permafrost SOC accumulation leads to a doubling of simulated LGM permafrost SOC storage (amounting to a total of ~ 150 PgC). Despite LGM temperatures favouring a larger permafrost extent, simulated cold glacial temperatures – together with low precipitation and low CO2 levels – limit vegetation productivity and therefore prevent a larger glacial SOC build-up in our model. Changes in physical and biogeochemical boundary conditions during deglacial warming lead to an increase in mineral SOC storage towards the Holocene (168 PgC at PI), which is below observational estimates (575 PgC in continuous and discontinuous permafrost). Additional model experiments clarified the sensitivity of simulated SOC storage to model parameters, affecting long-term soil carbon respiration rates and simulated active layer depths. Rather than a steady increase in carbon release from the LGM to PI as a consequence of deglacial permafrost degradation, our results suggest alternating phases of soil carbon accumulation and loss as an effect of dynamic changes in permafrost extent, active layer depths, soil litter input, and heterotrophic respiration.

scholarly journals The CCSM4 Land Simulation, 1850–2005: Assessment of Surface Climate and New Capabilities

2012 ◽  
Vol 25 (7) ◽  
pp. 2240-2260 ◽  
Author(s):  
David M. Lawrence ◽  
Keith W. Oleson ◽  
Mark G. Flanner ◽  
Christopher G. Fletcher ◽  
Peter J. Lawrence ◽  
...  
Keyword(s):  
Land Use ◽  
Air Temperature ◽  
Climate Simulation ◽  
Biogeochemical Model ◽  
Earth System ◽  
Climate System Model ◽  
Community Land Model ◽  
Model Version ◽  
Surface Climate ◽  
Global Land

Abstract This paper reviews developments for the Community Land Model, version 4 (CLM4), examines the land surface climate simulation of the Community Climate System Model, version 4 (CCSM4) compared to CCSM3, and assesses new earth system features of CLM4 within CCSM4. CLM4 incorporates a broad set of improvements including additions of a carbon–nitrogen (CN) biogeochemical model, an urban canyon model, and transient land cover and land use change, as well as revised soil and snow submodels. Several aspects of the surface climate simulation are improved in CCSM4. Improvements in the simulation of soil water storage, evapotranspiration, surface albedo, and permafrost that are apparent in offline CLM4 simulations are generally retained in CCSM4. The global land air temperature bias is reduced and the annual cycle is improved in many locations, especially at high latitudes. The global land precipitation bias is larger in CCSM4 because of bigger wet biases in central and southern Africa and Australia. New earth system capabilities are assessed. The present-day air temperature within urban areas is warmer than surrounding rural areas by 1°–2°C, which is comparable to or greater than the change in climate occurring over the last 130 years. The snow albedo feedback is more realistic and the radiative forcing of snow aerosol deposition is calculated as +0.083 W m−2 for present day. The land carbon flux due to land use, wildfire, and net ecosystem production is a source of carbon to the atmosphere throughout most of the historical simulation. CCSM4 is increasingly suited for studies of the role of land processes in climate and climate change.

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