It isn’t. Well, it is a little, but not totally. OK, it is, but actually, it is complicated.
First, you are probably asking about the Atlantic hurricane season, not the global issue of hurricanes and typhoons and such. If you are asking world-wide, recent prior years were worse if counted by how many humans killed and how much damage done.
With respect to the Atlantic, this was a bad year and there are special features of this year that were bad in a way that is best accounted for by global warming. But looking at the Atlantic hurricanes from a somewhat different but valid perspective, last year was worse (so far) and this year is ordinary, within the context of global warming. So, let’s talk about the global warming question first.
How Global Warming Makes Hurricane Seasons Worse
The effects of global warming on hurricanes in the Atlantic have two interesting features that must be understood to place this discussion in proper context.
First, we are having a bunch of bad decades in a row probably because of global warming. If we compare pre-1980, for a decade, with post 1980, or pre vs. post 1990, or anything similar, the more recent years have had more hurricanes than the earlier years. Comparing to even earlier time periods is tricky because of differences in available data (Satellites make a difference, probably, even with giant weather features like hurricanes). This is mainly due to increasing sea surface temperatures, but there are other factors as well.
Hurricanes are more likely to form when sea surface temperatures are higher. Higher sea surface temperatures can make a hurricane larger or stronger. Hurricanes will last longer if there is more, higher, hurricane-hot sea to travel over. If sea surface temperatures are high enough to cause hurricanes earlier in the year or later in the year, the hurricane season can be longer. Possibly, storms that in a non-warmed world would not have made it to “named storm” status are moved to that level of strength and organization because of the elevated sea surface temperature.
Sea surface temperature increases of small amounts cause large changes in hurricanes, and large changes in hurricanes cause larger changes in potential damage level. The increase in Atlantic sea surface temperatures over recent decades have probably been sufficient, according to my thumb-suck estimate that I strongly suspect is close to correct, to make about half the hurricanes that would have existed anyway jump up one category. Then, when hurricanes get stronger, the amount of damage they can do goes up exponentially. So the sea surface temperature increases we’ve see with global warming easily explain the fact that we’ve had more hurricanes overall, and stronger ones, over the last twenty or thirty years than during the previous years back to when the data are still pretty good.
Second, the science says this will get worse. There is one 2007 study (by Vecci and Soden, in Geophysical Research Letters) that suggests that maybe in the Atlantic, smaller size hurricanes will be less likely to form because of increased vertical wind shear, but that study does not mean much for larger or stronger hurricanes. This decade old study is constantly cited as evidence that global warming will not increase hurricanes in the Atlantic. Other studies show that the overall amount of hurricane activity, and the potential higher end of hurricane strength, and the size, and the speed at which they form, and the amount of water they can contain, and possibly the likelihood of a hurricane stalling right after landfall, go up. Up. Up. Up. One study says down and that word, “down” it resonates across the land like a sonic boom. The other studies say we can expect, and to varying degrees already see, up, up, up, up, up, and denial makes words like “up” and “more” and “worse” and “exasperated” dangerously quiet. Please don’t fall into that trap. Oh, by the way,the one study that says “down” has not been replicated and though experts feel it has some merit, it is far from proven and there are reasons to suggest it my be problematic.
Comparing the 2017 Atlantic Hurricane Season to Other Years
Funny thing about hurricanes: They exist whether or not they menace you. Every year a certain number of hurricanes (usually) form and wander about in the Atlantic ocean for a while, maybe hitting some boats, but otherwise doing little more than causing some big waves to eventually reach beaches in the Caribbean or the eastern US.
This year, we’ve had four major hurricanes so far. Harvey, which maxed out as a Cat 4, ravaged and flooded Texas and Louisiana. Irma, maxing at Cat 5, ravaged Florida after wiping out islands in the Leewards and doing great damage to Cuba and elsewhere in the Caribbean. Maria, maxing out as a Cat 5, did major damage in the Leewards and notably wiped out Puerto Rico. So, four Major Hurricanes formed in the Atlantic and hit something major.
Meanwhile, Jose, another Major hurricane at Cat 4 status, still spinning about in the North Atlantic, is one of those that hit nothing. And that’s all so far this year.
Last year, there were almost exactly the same number of named storms in total (so far) and just like 2017, 2016 had four major hurricanes.
You remember Matthew, which scraped the Atlantic coast and was rather damaging. But do you remember Gaston (Cat 3)? Nicole (Cat 4)? Otto (Cat 3)?
Gaston and Nicole wandered about in the Atlantic and hit nothing. Otto was for real, it hit Central America, but not the US, so from the US perspective, it counts as a non-hitting hurricane. Also, it was only barely cat 3 and weakened quickly.
From 2000 to 2016, inclusively, we have had an average of 15 named storms per year, with a minimum of 8 and a maximum of 28, with most years being between 10 and 16. So far 2017 has had 13 named storms. We may have a couple more. So, likely, we will be right in the middle.
For the same period, the number of hurricanes has ranged from 2 to 15 with an average of about 7. This year, we have had … wait for it … 7. We may or ma not get another one, not very likely two more. In other words, this is an average year for the number of hurricanes.
For the same period, the number of major hurricanes ranges from 0 (though only one year ad zero, it is more typical to have 2 in a low year) to 7, but again, 7 is extreme. It is usually from 2-5. The average is just over 3. This year, we have four. That’s pretty typical.
So, within the context that the last couple of decades has had a somewhat higher than average frequency of hurricanes, and probably more strong ones than previous decades, this we had a typical year this year.
Why does it feel different? Why is it in fact difference, with respect to the horror of it all? Because we had more landfalls, and more serious landfalls.
Keep in mind that Harvey could have hit Houston differently and done more damage. Keep in mind that Cuba beat up Irma, then Irma failed to strike Florida in just the right way to do maximum damage. Keep in mind that after wiping out Puerto Rico, Maria swerved quickly out to sea. In other words, keep in mind that this year could have been much worse than it was.
This is the point that you must understand: Any year can be like this year, or worse. And, with increasing sea surface temperatures and other global warming related factors, worse still.