In a comment on a 2017 paper by Cheung et al., Kravtsov states that the results of Cheung et al. are invalidated by errors in the method used to estimate internal variability in historical surface temperatures, which involves using the ensemble mean of simulations from phase 5 of the Coupled Model Intercomparison Project (CMIP5) to estimate the forced signal. Kravtsov claims that differences between the forced signals in the individual models and as defined by the multimodel ensemble mean lead to errors in the assessment of internal variability in both model simulations and the instrumental record. Kravtsov proposes a different method, which instead uses CMIP5 models with at least four realizations to define the forced component. Here, it is shown that the conclusions of Cheung et al. are valid regardless of whether the method of Cheung et al. or that of Kravtsov is applied. Furthermore, many of the points raised by Kravtsov are discussed in Cheung et al., and the disagreements of Kravtsov appear to be mainly due to a misunderstanding of the aims of Cheung et al.
Bibliographical noteFunding Information:
Acknowledgments. We acknowledge the World Climate Research Programme’s Working Group on Coupled Modelling, which is responsible for CMIP, and we thank the climate modeling groups for producing and making available their model output. AHC acknowledges support from the U.S. National Science Foundation (AGS-1263225). MHE and LMF are supported by the Australian Research Council. We thank S. Kravtsov for making his data available. Kaplan SST version 2 data are provided by the NOAA/OAR/ESRL PSD, Boulder, Colorado, from their website at http://www.esrl.noaa. gov/psd/. HadISST data are provided by the Met Office Hadley Centre (online at http://www.metoffice.gov.uk/ hadobs). ERSST data are provided by NOAA (online at http://www.ncdc.noaa.gov/data-access/marineocean-data/ extended-reconstructed-sea-surface-temperature-ersst-v3b).
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- Interannual variability
- Interdecadal variability
- Multidecadal variability
- North Atlantic Ocean
- North Pacific Ocean
- Northern Hemisphere