ReviewATMOSPHERIC SCIENCE

Context for interpreting equilibrium climate sensitivity and transient climate response from the CMIP6 Earth system models

See allHide authors and affiliations

Science Advances  24 Jun 2020:
Vol. 6, no. 26, eaba1981
DOI: 10.1126/sciadv.aba1981

Figures

  • Fig. 1 Historical values of ECS and TCR.

    Assessed values of ECS (blue bars) and TCR (red bars), ranges from models of ECS (orange bars), and TCR (green bars; single value from the AR1 is green dot); numbers are individual model values of ECS from CMIP5 and CMIP6 (available on the ESGF as of March 2020). The numbers denoting individual models for CMIP5 are listed in Table 1 and those for CMIP6 in Table 2. Sources for values: AR1: table 3.2a of [IPCC First Assessment Report Ch. 3 (5)]; (ECS, 19 models with variable clouds; TCR, 1 model). AR2/CMIP1: figure 6.4 and table 6.3 of [IPCC Second Assessment Report Ch. 6 (18)] (ECS, 9 models; TCR, 13 models). AR3/CMIP2: table 9.1 of [IPCC Third Assessment Report, Ch. 9 (20)] (ECS, 14 models; TCR, 19 models). AR4/CMIP3: figure 10.25 of [IPCC Fourth Assessment Report Ch. 10 (21)] (ECS and TCR, 19 models). AR5/CMIP5: figure 9.42 and table 9.5 of [IPCC Fifth Assessment Report Ch. 9 (25)] (ECS, 23 models; TCR, 30 models; this differs somewhat from currently available CMIP5 models in the ESGF in Table 1). CMIP6: ECS (37 models) and TCR (37 models), with data available from a total of 39 models on the ESGF in March 2020 (Table 2).

  • Fig. 2 ECS as a function of TCR.

    (A) From the CMIP5 models in the IPCC AR5 (black line is linear fit); (B) same as (A) except for CMIP6 models (black line is a linear fit). Note that 27 models are plotted for CMIP5 (Table 1) compared to a total of 23 and 30 models that supplied ECS and TCR values, respectively, to the IPCC AR5 used for the ranges in Fig. 1. The greater number of models plotted here denotes those with sufficient available data on the ESGF to perform corresponding ECS and TCR calculations, as defined in the ESMValTool discussed in the text. The R2 values are given in the upper left parts of each panel. The numbers denoting individual models for CMIP5 in (A) are listed in Table 1 and those for CMIP6 in (B) in Table 2.

  • Fig. 3 ECS calculated for the CMIP6 models in Table 2 using the Gregory method over different time scales.

    Using the entire 150-year 4xCO2 experiment (black line), there is an ECS value of 3.7°C; using only the first 20 years (blue dots and blue line), there is an ECS of 3.3°C; and using the last 130 years, there is an ECS of 4.0°C (orange dots and orange line).

  • Fig. 4 Effective radiative forcing from aerosols versus ECS.

    Values supplied by the modeling groups (Table 3); black line is linear fit with R2 of 0.36. The numbers denoting individual models are listed in Table 2.

Tables

  • Table 1 ECS and TCR values (°C) calculated from CMIP5 model data available on the ESGF in March 2020.

    Model numbers denote individual models (in second column) in Figs. 1, 2, and 4. Model acronyms are defined at https://pcmdi.llnl.gov/mips/cmip5/availability.html.

    CMIP5 model
    number
    ModelECSTCR
    1ACCESS1-03.81.9
    2ACCESS1-33.51.6
    3BNU-ESM3.92.5
    4CCSM42.91.7
    5CNRM-CM53.32.0
    6CNRM-CM5-21.8
    7CSIRO-Mk3-6-04.11.7
    8CanESM23.72.3
    9FGOALS-g23.41.4
    10FGOALS-s24.22.4
    11GFDL-CM34.01.9
    12GFDL-ESM2G2.41.1
    13GFDL-ESM2M2.41.4
    14GISS-E2-H2.31.7
    15GISS-E2-R2.11.5
    16HadGEM2-ES4.62.5
    17IPSL-CM5A-LR4.12.0
    18IPSL-CM5A-MR2.0
    19IPSL-CM5B-LR2.61.5
    20MIROC-ESM4.72.2
    21MIROC52.71.4
    22MPI-ESM-LR3.62.0
    23MPI-ESM-MR3.52.0
    24MPI-ESM-P3.52.0
    25MRI-CGCM32.61.6
    26NorESM1-M2.81.4
    27bcc-csm1-12.81.7
    28bcc-csm1-1-m2.92.1
    29inmcm42.11.3
    Multimodel mean3.21.8
    SD0.70.4
  • Table 2 ECS and TCR values (°C) calculated from CMIP6 model data available on the ESGF in March 2020.

    Model numbers denote individual models (in second column) in Figs. 1, 2, and 4. Model acronyms are defined at https://wcrp-cmip.github.io/CMIP6_CVs/docs/CMIP6_source_id.html, and modeling groups at https://wcrp-cmip.github.io/CMIP6_CVs/docs/CMIP6_source_id.html.

    CMIP6 model
    number
    ModelECSTCR
    30ACCESS-CM24.72.1
    31ACCESS-ESM1-53.92.0
    32AWI-CM-1-1-MR3.22.0
    33BCC-CSM2-MR3.01.7
    34BCC-ESM13.31.8
    35CAMS-CSM1-02.31.7
    36CESM25.22.0
    37CESM2-WACCM4.82.0
    38CNRM-CM6-14.82.1
    39CNRM-CM6-1-HR4.32.5
    40CNRM-ESM2-14.81.9
    41CanESM55.62.7
    42E3SM-1-05.33.0
    43EC-Earth34.3
    44EC-Earth3-Veg4.32.6
    45FGOALS-f3-L3.02.1
    46GFDL-CM43.92.1
    47GFDL-ESM42.61.6
    48GISS-E2-1-G2.71.8
    49GISS-E2-1-H3.11.9
    50GISS-E2-2-G2.41.7
    51HadGEM3-GC31-LL5.62.6
    52HadGEM3-GC31-MM5.42.6
    53IITM-ESM1.7
    54INM-CM4-81.81.3
    55INM-CM5-01.9
    56IPSL-CM6A-LR4.62.3
    57KACE-1-0-G4.51.4
    58MCM-UA-1-03.71.9
    59MIROC-ES2L2.71.6
    60MIROC62.61.6
    61MPI-ESM1-2-HR3.01.7
    62MPI-ESM1-2-LR3.01.8
    63MRI-ESM2-03.21.6
    64NESM34.72.7
    65NorCPM11.6
    66NorESM2-LM2.51.5
    67SAM0-UNICON3.72.3
    68UKESM1-0-LL5.32.8
    Multimodel mean3.72.0
    SD1.10.4
  • Table 3 Subsample of CMIP6 models shown in Fig. 1, with information supplied by the modeling groups regarding details of aerosol forcing and formulation and possible reasons for ECS values.

    For the GFDL models, the higher sensitivities in parentheses denoted by asterisks result from longer runs and attempts to filter out unforced variability. Model acronyms are defined at https://wcrp-cmip.github.io/CMIP6_CVs/docs/CMIP6_source_id.html, and modeling groups at https://wcrp-cmip.github.io/CMIP6_CVs/docs/CMIP6_source_id.html.

    ModelECS (K)TCR (K)Aerosol ERF
    (W m2)
    Aerosol schemeReasons for ΔECS from CMIP5?Paper for more
    information
    E3SM_15.33.0−1.65Prognostic—direct and
    indirect
    No CMIP5 equivalent but unusually
    large positive SW cloud feedback
    Golaz et al. (61)
    CESM2
    CESM2-WACCM
    5.3
    4.8
    2.0
    1.9
    −1.67Prognostic—direct and
    indirect
    Increase by >1k from CESM1 related
    to cloud feedbacks and
    aerosol-cloud interactions
    Gettelman et al. (49)
    GFDL-CM4
    GFDL-ESM4
    3.9 (5.0*)
    2.7 (3.4*)
    2.1
    1.6
    −0.7
    −0.7
    Prognostic—direct and
    indirect
    Preliminary investigation into the
    causes for this lower climate
    sensitivity in ESM4.1 compared to
    CM4.0 have indicated at least six
    drivers (3 –ve aerosol-climate
    feedbacks, −ve stratospheric
    ozone feedback, changes in ocean
    heat uptake, explicit
    representation of CO2)
    Held et al. (62)
    Winton et al. (63)
    HadGEM3-GC3.1-LL
    UKESM1
    5.5
    5.4
    2.6
    2.8
    −1.1
    −1.17
    Prognostic—direct and
    indirect
    Cloud-aerosol interactions and cloud
    microphysics
    Bodas-Salcedo et al. (50)
    Andrews et al. (64)
    Sellar et al. (65)
    MIROC62.61.6−0.76Prognostic—direct and
    indirect(?) (SPRINTARS)
    Very little change from CMIP5
    to CMIP6
    Tatebe et al. (66)
    MRI-ESM23.11.6−1.22Prognostic—direct and
    indirect effects
    Small increase in sensitivity (2.6–3.1)
    and many changes having a small
    impact, with largest impact possibly
    coming from changes to
    entrainment-detrainment rates
    (but not yet fully tested)
    Yukimoto et al. (67)
    MPI-ESM1.23.0−0.6Specified, direct only
    (MACv2-SP)
    Tuned with cloud parameters to be
    the same as CMIP5. Pretuned
    version had ECS = 7 caused by
    a +ve low-cloud feedback in the
    tropics
    Mauritsen et al. (68)
    EC-Earth3
    EC-Earth3-veg
    4.2
    4.3
    2.6Not yet
    known
    Specified, direct only
    (MACv2Sp)
    Early indications of the role of
    cloud-aerosol interactions
    Wyser et al. (69)
    INM-CM5
    INM-CM4.8
    1.9
    1.8
    1.3−0.5Prognostic—direct
    effect only
    No change in ECS from CMIP5
    although a lot of changes in
    parametrization of cloud and
    condensate
    ACCESS-CM2
    ACCESS-ESM1.5
    4.7
    3.9
    Not yet
    known
    Prognostic—direct and
    indirect
    Using HadGEM3-GC3.1 atmospheric
    component, so high ECS aligned to
    this
    Using ACCESS1.3 CMIP5 model
    physics—little change
    AWI-ESM3.22.2Not knownSpecified—direct
    (MACv2Sp)
    No CMIP5 model, but interesting
    from the “parent” model, MPI-ESM
    CanESM55.622.7Prognostic—direct and
    indirect effect
    Large increase since CMIP5 model
    (3.7–5.6)—at least half seems to
    be related to cloud feedback
    increase
    Swart et al. (70)
    Paper on cloud
    feedbacks and ECS
    paper planned for
    2020
    NorESM2-LM2.5−1.2Prognostic—direct and
    indirect
    Small decrease since CMIP5 model
    (2.9–2.5), which is not yet
    understood
    Paper hoped for in
    early 2020
    IPSL-CM6A-LR4.62.3−0.6Specified—direct and
    indirect
    Lurton et al. paper
    planned for 2020
    Servonnat et al. paper
    planned for 2020

Stay Connected to Science Advances

Navigate This Article