A good visualization, though it comes with the usual caveat that our records become sporadic before the 1960s (satellite data), with meteorologists in universal accord that some storms were completely missed back then.
It is also important to remember that seasonal hurricane activity is primarily dictated by natural cycles such as the Atlantic Multidecadal Oscillation, and not the background climate change signal. The AMO flipped phases in 1995, resulting in conditions generally becoming much more favorable for tropical cyclone activity in the Atlantic since then. 1970-1994 specifically (the last suppressed AMO phase) exhibited many extremely inactive seasons. In 1994, The Atlantic had 7 storms, 3 hurricanes, and 0 major hurricanes. One season later in 1995, there were 19 storms, 11 hurricanes, and 5 majors. Is this dramatic shift due to another 0.05C of warming, or is it due to a shift in conditions due to natural climate cycles? It’s the latter.
The effects of climate change act to increase moisture content and increase frequency of rapid intensification.. as well as the intensity ceiling of tropical cyclones. But the link to tropical cyclone frequency is much more dubious. It’s very difficult to correlate a statistically significant signal regarding TC frequency to climate change. I am talking about overall, globally here. There are certain specific regions of different basins which do exhibit an increase. Natural parameters like ENSO, the AMO, and intraseasonal MJO activity dominate the climate change signal.
2024 exhibited the warmest Atlantic Tropics in our records. And late August to mid September is historically the most active part of the season. Yet in 2024, zero storms formed between 20 August and 9 September. Is that also climate change? The reality is that natural variability (such as an unfavorable MJO phase) dominated the climate change signal, resulting in no activity. There were other factors responsible for that lull; I am simplifying quite a bit here to make a point.
Climate change induced warming may have actually helped create last seasons’ lull, to be honest. Climate change induced asymmetric warming of the Poles expands the Hadley cells, which results in stronger subtropical ridging and higher geopotential heights. Higher heights and stronger ridging result in vertically sinking air/subsidence, and sinking air compresses itself which induces adiabatic warming of the atmospheric column. Thunderstorms are a function of vertical gradience in temperature: specifically, between the ocean surface and tropopause. When temperatures aloft warm, this decreases the vertical temperature gradient which lowers lapse rates and therefore stabilizes the atmosphere. This means less thunderstorm activity which translates to fewer tropical cyclones. Warming the tropopause has the same thermodynamic effect on deep convection as cooling the sea surface temperatures.
Here is more about 2024, including its peak-season lull, from TSR:
https://www.tropicalstormrisk.com/docs/TSRATL2024Verification.pdf
Specifically,
https://i.imgur.com/3Yh0dns.png
And more from CSU:
https://tropical.colostate.edu/Forecast/2024_0903_seasondiscussion.pdf
Specifically,
In addition to the extremely warm sea surface temperatures, upper ocean heat content is at near-records levels as well, with values close to what were observed in 2023 at this time (Figure 13). So from a sea surface temperature/ocean heat perspective, the Atlantic hurricane season should be extremely active.
However, compared with 2023, upper-tropospheric temperatures are warmer this year in the MDR (Figure 14). This increase in upper-tropospheric temperatures may be causing a stabilizing effect that is suppressing deep convection across the MDR.
Historically, there has not been much of a relationship between the difference in upper level temperatures minus SST, but the upper-level temperatures are much warmer relative to SSTs in 2024 than they were in any other year (Figure 15). Perhaps this is a sign that upper-tropospheric warming, likely linked to El Niño on annual timescales and anthropogenic warming on decadal timescales, could cause additional stability issues in future years.
I just want to get ahead of the conversation here. Climate change is real and is forced by human activity. It has effects on tropical cyclones. Its effects are overall net-positive for storms (higher intensities). But it is not even close to the only factor at play here and the interaction between climate, its change over time, and hurricanes is so unfathomably complex that there will always be nuance which remains undiscussed. Particularly on social media platforms.. where nuance goes to die. Never outright dismiss climate change as an effect, but never overexaggerate it, either. It makes the public less trusting of scientists when you do this.