Question: How is climate change impacting hurricanes now and what’s expected in the future?
Nadir’s Answer: Natural fluctuations are indeed a feature of Earth’s climate. But, if we look at the climate of the past 150 years (for which we have direct temperature measurements) and compare to climate models, we find that the observed warming of the past 30 years or so is outside the range of natural fluctuations produced by models. Furthermore, models can only reproduce this warming when forced with the historically observed CO₂ increases (see Fig.1 of FAQ 10.1 of the last IPCC report).
Models are not perfect, of course, so we’d like to have another line of evidence which doesn’t rely on them. One such line of evidence is that warming from natural fluctuations would draw heat from the deep ocean and into the atmosphere, but we instead find that the deep ocean is warming at the same time as the atmosphere (see Fig. 2 of Cheng et al. 2017 below). For people who want to delve more deeply into this topic, I recommend FAQ 10.1 of Ch. 10 of IPCC 2013 and Climate Change: Evidence and Causes, NAS.