TY - JOUR
T1 - Natural variability contributes to model–satellite differences in tropical tropospheric warming
AU - Po-Chedley, Stephen
AU - Santer, Benjamin D.
AU - Fueglistaler, Stephan
AU - Zelinka, Mark D.
AU - Cameron-Smith, Philip J.
AU - Painter, Jeffrey F.
AU - Fu, Qiang
N1 - Funding Information:
ACKNOWLEDGMENTS. We thank the World Climate Research Program, which, through its Working Group on Coupled Modeling, coordinated and promoted CMIP6. We thank the climate modeling groups for producing and making available their model output; the ESGF for archiving the data and providing access; and the multiple funding agencies that support CMIP6 and ESGF. We acknowledge high-performance computing support from Cheyenne (DOI: 10.5065/D6RX99HX) provided by the National Center for Atmospheric Research’s Computational and Information Systems Laboratory, sponsored by the NSF, which was used for initial AMIP experiments. Work at Lawrence Livermore National Laboratory (LLNL) was performed under the auspices of US Department of Energy Contract DE-AC52-07NA27344. S.P.-C. was supported by LLNL Laboratory Directed Research and Development Program (18-ERD-054). P.J.C.-S. was supported by the Energy Exascale Earth System Model project, funded by the US Department of Energy, Office of Science, Office of Biological and Environmental Research. M.D.Z. was supported by the Regional and Global Model Analysis Program of the Office of Science at the US Department of Energy. The views, opinions, and findings contained in this report are those of the authors and should not be construed as a position, policy, or decision of the US Government or the US Department of Energy.
Publisher Copyright:
© 2021 National Academy of Sciences. All rights reserved.
PY - 2021/3/30
Y1 - 2021/3/30
N2 - A long-standing discrepancy exists between general circulation models (GCMs) and satellite observations: The multimodel mean temperature of the midtroposphere (TMT) in the tropics warms at approximately twice the rate of observations. Using a large ensemble of simulations from a single climate model, we find that tropical TMT trends (1979–2018) vary widely and that a subset of realizations are within the range of satellite observations. Realizations with relatively small tropical TMT trends are accompanied by subdued sea-surface warming in the tropical central and eastern Pacific. Observed changes in sea-surface temperature have a similar pattern, implying that the observed tropical TMT trend has been reduced by multidecadal variability. We also assess the latest generation of GCMs from the Coupled Model Intercomparison Project Phase 6 (CMIP6). CMIP6 simulations with muted warming over the central and eastern Pacific also show reduced tropical tropospheric warming. We find that 13% of the model realizations have tropical TMT trends within the observed trend range. These simulations are from models with both small and large climate sensitivity values, illustrating that the magnitude of tropical tropospheric warming is not solely a function of climate sensitivity. For global averages, one-quarter of model simulations exhibit TMT trends in accord with observations. Our results indicate that even on 40-y timescales, natural climate variability is important to consider when comparing observed and simulated tropospheric warming and is sufficiently large to explain TMT trend differences between models and satellite data.
AB - A long-standing discrepancy exists between general circulation models (GCMs) and satellite observations: The multimodel mean temperature of the midtroposphere (TMT) in the tropics warms at approximately twice the rate of observations. Using a large ensemble of simulations from a single climate model, we find that tropical TMT trends (1979–2018) vary widely and that a subset of realizations are within the range of satellite observations. Realizations with relatively small tropical TMT trends are accompanied by subdued sea-surface warming in the tropical central and eastern Pacific. Observed changes in sea-surface temperature have a similar pattern, implying that the observed tropical TMT trend has been reduced by multidecadal variability. We also assess the latest generation of GCMs from the Coupled Model Intercomparison Project Phase 6 (CMIP6). CMIP6 simulations with muted warming over the central and eastern Pacific also show reduced tropical tropospheric warming. We find that 13% of the model realizations have tropical TMT trends within the observed trend range. These simulations are from models with both small and large climate sensitivity values, illustrating that the magnitude of tropical tropospheric warming is not solely a function of climate sensitivity. For global averages, one-quarter of model simulations exhibit TMT trends in accord with observations. Our results indicate that even on 40-y timescales, natural climate variability is important to consider when comparing observed and simulated tropospheric warming and is sufficiently large to explain TMT trend differences between models and satellite data.
KW - Climate change
KW - General circulation models
KW - Natural climate variability
KW - Satellite data
UR - http://www.scopus.com/inward/record.url?scp=85102918017&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=85102918017&partnerID=8YFLogxK
U2 - 10.1073/pnas.2020962118
DO - 10.1073/pnas.2020962118
M3 - Article
C2 - 33753490
AN - SCOPUS:85102918017
SN - 0027-8424
VL - 118
JO - Proceedings of the National Academy of Sciences of the United States of America
JF - Proceedings of the National Academy of Sciences of the United States of America
IS - 13
M1 - e2020962118
ER -