Text S2.
Autocorrelation of WCTH
Much of the autocorrelation in WCTH is dominated by the ENSO cycle,
which has been found to have decorrelation times between 6 and 10 months
(Berner et al., 2020; Burgers & van Oldenborgh, 2003). Autocorrelation
functions of WCTH are shown in Figure S3 where it can be seen
that in each of the five latitude bands the autocorrelation is well
below the e-fold point (indicated by the red line) within 12 months lag.
Sensitivity tests were performed to determine what block length is
acceptable. In the tropics the moving block resampling scheme was
applied to the WCTH averaged over the tropics (the region with the
latest decorrelation) using 6-, 12-, 24-, and 48-month block lengths.
There is no significant difference using a block length of 24 or 48
months, however results based on lengths below 24 months differ
substantially, and so a block length of 2 years was used for all results
shown in the main text.
Berner, J., Christensen, H. M., & Sardeshmukh, P. D. (2020). Does ENSO
regularity increase in a warming climate? Journal of Climate ,33 (4), 1247–1259. https://doi.org/10.1175/JCLI-D-19-0545.1
Burgers, G., & van Oldenborgh, G. J. (2003). On the impact of local
feedbacks in the central Pacific on the ENSO cycle. Journal of
Climate , 16 (14), 2396–2407. https://doi.org/10.1175/2766.1