Except the argument isn't about the frequency of storms nor the occurrence of a severe storm, but the increase in frequency of severe storms. Essentially, if we put more energy into the system, then we shouldn't be surprised if more energy is outputted as a result of the same system.
> A sustained upward trend is found between the global proportion of Cat 4–5 hurricanes and ACCI (Fig. 4), balanced by a similar decrease in Cat 1–2 hurricanes. The results are independent of the choice of models to calculate the ACCI as can be seen by comparing Fig. 4a and b. In both cases the ACCI explains 80–85 % of the variance in the smoothed annual hurricane proportions with p < 0.01 (using unsmoothed data). This finding is consistent with the SST-related increases in Cat 4–5 and decreases in Cat 1–2 found by Kishtawal et al. (2012), the relationship of intense hurricanes with SST found by Hoyos et al. (2010), and the Atlantic landfall hurricane changes noted by Grinsted et al. (2012).
> A sustained upward trend is found between the global proportion of Cat 4–5 hurricanes and ACCI (Fig. 4), balanced by a similar decrease in Cat 1–2 hurricanes. The results are independent of the choice of models to calculate the ACCI as can be seen by comparing Fig. 4a and b. In both cases the ACCI explains 80–85 % of the variance in the smoothed annual hurricane proportions with p < 0.01 (using unsmoothed data). This finding is consistent with the SST-related increases in Cat 4–5 and decreases in Cat 1–2 found by Kishtawal et al. (2012), the relationship of intense hurricanes with SST found by Hoyos et al. (2010), and the Atlantic landfall hurricane changes noted by Grinsted et al. (2012).
Diagram: https://static-content.springer.com/image/art%3A10.1007%2Fs0...
https://link.springer.com/article/10.1007/S00382-013-1713-0