We obtain new insights into the reliability of long-term historical Atlantic tropical cyclone (‘TC’) counts through the use of a statistical model that relates variations in annual Atlantic TC counts to climate state variables. We find that the existence of a substantial undercount bias in late 19th through mid 20th century TC counts is inconsistent with the statistical relationship between TC counts and climate.Mann, Sabetelli and Neu find that the undercount is one (1.2 to be precise) by comparing the observed number of Atlantic tropical cyclones to that predicted using three proxys: sea surface temperature, El Nino and NAO indicies. The undercount bias is adjusted to give the best fit.
UPDATE: In the comments Henry Anonymouse asked for the full Fig. 1. (see below). By eyeball, it is pretty clear that the sea surface temperature is the driver, with El Nino and the NAO serving as modulating factors.