alt Hacker NewsYes I was wondering the same. Why is the mean using a different set of years than the total data set? There also seems to be a year where the swing was equally as extreme in the other direction, what year was this? Would be worth mentioning at least in the post.
Based on https://climatereanalyzer.org/clim/sst_daily/?dm_id=nino3.4, 1988 is the year from the dataset with the lowest temperature throughout June and July.