In fairness though, they didn't just make up their bias assertion; it's in other published works[1] and there is real evidence that old measurements were incorrect (biased towards the high side) when compared to other available contemporary measurements.
[1]: Landsea, C. W. Mon. Weath. Rev. 121, 1703–1714 (1993) - https://journals.ametsoc.org/configurable/content/journals$0...