by Nic Lewis, Jan 19, 2021 in ClilmateEtc.
- The pattern effect is the dependence of outgoing radiation to space on the spatial pattern of surface warming.
- A pattern effect, relative to that in equilibrium, can be caused both by evolution over time in the climate system’s response to forcing and by its internal variability.
- The paper fails to distinguish between a historical period pattern effect that is forced, which will unwind very slowly, and one that is caused by internal variability, which can quickly unwind, causing rapid warming.
- The forced pattern effect is very small in CAM5.3
- The pattern effect found in the paper is greatly affected by being estimated during the hiatus.
- The estimated post-hiatus unforced historical pattern effect is non-negligible in CAM5.3 when using the AMIP2 sea surface temperature dataset, as in the paper, but negligible when using the UK Met Office HadISST1 dataset.
- The historical pattern effect is not robust; it varies hugely between models and SST datasets.
- The paper’s claims about greater committed warming directly reflect its estimate of the size of the historical pattern effect.
A new paper “Greater committed warming after accounting for the pattern effect” led by Chen Zhou (Zhou et al.) has recently been published in Nature Climate Change. Here is the accompanying press release.