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.
As you already know, Hurricane Maria is a Category 5 storm menacing the Leewards, and heading, likely, for Puerto Rico.
Please avoid making the mistakes that were made in talking about Irma. There will probably be no Category 5 storm hitting Puerto Rico. The storm will probably be a Category 4 before it hits. So, reporters will sloppily declare that “a category 5 storm is heading for Puerto Rico” then later Rush Limberger will say “Look there was never no such storm, see?” and so on.
But, a Category 4 storm is still nothing to sneeze into, and Puerto Rico and the other island in this storm’s path are in big trouble.
As we wait for that to develop further, let’s talk a bit about predicting hurricane seasons. A lot of people are arguing about whether or not global warming means more, or bigger, or whatever, Atlantic hurricanes. (Short answer: there are probably already more hurricanes in the Atlantic, and bigger ones, but they are hard to count because they are in fact rare events, and science says that there will likely be more in the future). One of the dumber counter arguments to science suggesting that there may be bigger storms, or more of them, is this: You can’t even predict the weather for next weekend, so what the heck, right?
The counter argument to that is this: Ok, fine, we don’t know very accurately what the weather is going to be like next weekend, but what would you say if I told you that we can do a pretty good job of telling, before the hurricane season starts, how many named storms there will be? Huh? Wouldn’t that be amazing?
Turns out we can. And the fact that we can suggests that we should be trusting the models, generally, and therefore, expecting more and bigger hurricanes.
I looked at the predictions made in several recent years by several groups that do this prediction, and found out that the total average wrongness averaging across all of them is down near one hurricane, with the range of wrongness being between -8 and 4, but with most of the predictions being within just a few one way or another.
First, a quick look at the number of named tropical storms in the Atlantic per year:
People will tell you there is no trend here, but as you can see, about 44% of the variation seen in the number of storms over time is accounted for by year, so there is a good argument that there is an increasing trend. One might argue that back in the 70s we missed some Hurricanes. That, I do not buy, but if you need to believe that, you can see there is still a trend from 1980 on. So there is an increase.
But I digress. Here’s the point I wanted to make with this graph. The number of hurricanes in a given year varies quite a bit, from 4 to 28 over this time period (and less over the most recent years). So, a method of prediction that gets within two or three in either direction is pretty good.
The number of named storms (many, usually most, of which will be hurricanes) that will happen in a give season in the Atlantic is predicted with reasonable accuracy by several groups. Here’s a chart showing several different prediction groups compared to reality.
The light blue line is the actual number, and you can see that except for 2011 and 2012, the number of storms predicted by various groups, and the number that occur, are very similar. Let’s assume 2011 and 2012 are strange years and arbitrarily ignore them (I know, this would normally be cheating but we’ll come back to that in a minute).
Looking only at those years, one prediction undershot by 4, one prediction undershot by 3, and 7 overshot by 3 or 4. The other 20 predictions were off by no more than two storms.
So, why is it OK to fudge the data like that? Well, it isn’t really, but the last two years of predictions have been off by one or fewer storms on average, and I’m assuming the predictions are getting better and better. In other words, if I were to lay odds on predicting three years in a row a few years in the future, I’d bet that the average difference between all the predictions an the actual observations would be less than one named storm, and I’d win that bet. For this reason I don’t care so much about older data.
Notice that I’m only using predictions made prior to the start of the season, not later updates which some groups do provide.
For this year, we’ve had 13 named storms so far, and all the various groups predicted 14. There is plenty of time to have a couple more storms, so likely, this year will be a bit more active than expected, but just by a couple of storms.
Back to Maria for a moment, you may be wondering if this storm will hit the coast along the lower 48. It is possible, it is too early to tell, but history and the models that exist so far both suggest that it probably will not, but stay tuned.