Climate change is making hurricanes and their impacts worse. But as with all aspects of hurricanes, the hows and whys are complicated. Just as we’re still learning about how hurricanes themselves work, there remains much to be done to fully understand how our warming climate is changing these storms.
Part of the reason for this uncertainty is that, while we have plenty of robust and trustworthy models that can predict how hurricanes will behave in the future, our actual physical data-collection capabilities are not quite as extensive. Hurricanes can’t be studied in the same way storms on land are, where we have weather-monitoring and data-gathering technology in everyone’s backyard. All we can do to study these water-based storms is fly a plane through them (which we only do with storms that threaten the U.S.) or look at them from above with a satellite. And our satellite data only goes back to the 1970s. That means trends and changes over time are hard to spot.
All that said, as every hurricane season passes, scientists are seeing that the storms are behaving just as the models are predicting. They are growing stronger, they are holding more water, they are dumping more rain, and they are causing bigger floods. But there are a few other nuanced and more mysterious changes happening with these storms that may or may not be the result of climate change. Here’s a look at what scientists knows for sure—and what they’re still trying to put a finger on.
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What We Know for Sure
The first thing that we know, without question, is that global sea-level rise will guarantee that the flooding consequences of hurricanes will be more dramatic. “As the climate warms, the sea level will rise. That’s a very certain prediction. That means even if the hurricanes stay exactly the same their impacts can be worse,” says Allison Wing, an atmospheric scientist at Florida State University.
The biggest impact from sea-level rise will come from storm surge—the rush of water that happens when hurricane winds and a rise in atmospheric pressure push water up onto the shore. According to Suzana Camargo, an ocean and climate physicist at the Lamont-Doherty Earth Observatory at Columbia University’s Earth Institute, “Even if you have exactly the same hurricane you had 100 years ago, you will have a higher-level storm surge because you’re starting from a higher sea level. That makes more flooding and that aspect is most robust and most certain. We know that’s an issue.”
The next indisputable impact of climate change on hurricanes is that a warming climate will increase the amount of water that a hurricane can hold. The laws of physics tell us that a warmer atmosphere can hold more water. It’s one of (several) reasons why tropical climates are more wet and humid. And it’s something we’ve seen in other areas of weather impacts from climate change—warmer weather means a lot more rain. “As the atmosphere gets warmer it can hold more moisture, and increases the intensity of downpours and rains you get. It’s basic physics,” says Wing.
So the most confident statement we can make about climate change and hurricanes, based on physical data, observation, and modeling, is that they are going to get a lot wetter.
What We Probably Know
The next level of surety has to do with the increasing intensity of storms. Scientists believe, based on models and some early observational evidence, that as the climate warms hurricanes are going to become stronger. This belief is based on a theory by meteorologist and atmospheric scientist Kerry Emmanuel called the Potential Intensity Theory. It states that if you have a bigger difference in temperature between the ocean water and the atmosphere above it, a storm will become stronger.
“Warmer climates support stronger storms,” says Emmanuel. “There’s a speed limit beyond which a hurricane cannot go. That depends on the temperature of the ocean and the whole atmosphere above it. When you warm the two fluids, the air and the water, global warming raises the speed limit.”
According to Camargo, the models very strongly support this theory. “That’s a very clear projection and that’s not only what the models are doing but we already have some observation of that.” She says for the most part, the models are showing a 10-to-15 percent increase in intensity, which she notes is a small change in the big picture.
Still, Wing points out that our own measurements are not robust enough to say for sure if this has started happening yet: “The models that we use tend to support that [theory]. The thing that’s uncertain is whether or not they've gotten stronger already. It’s hard to say because hurricanes are a pretty rare event and there's a lot of variability from one year to the next. In addition, we don’t have reliable observations of intensity for very long. They only go back to the ’70s when we had satellites. It makes it hard to say what’s happened so far.”
What We’re Not Quite Sure About
One of the big remaining questions about how climate is impacting hurricanes has to do with the number of hurricanes we have every year. Right now there are about 90 hurricanes per year across the planet. Scientists are not quite sure why. And the lack of knowledge about what causes that very reliable number is creating a bit of a stir—because hurricane models are showing us that as the climate gets warmer there will probably be fewer hurricanes.
“I would say that right now our best guess is that in the future there will be fewer hurricanes or about the same. That’s very uncertain because that’s just what the models say and we don’t have a physical theory for why,” says Wing. “Since we don’t have the basic knowledge about what controls them, it’s hard to say what will happen in the future. So we can run our models but we don’t have the second line of evidence. That’s one of the biggest open questions in meteorology. What controls the number of cyclones each year?”
Camargo also points out that, while most models are showing that there will be fewer hurricanes, there are a few that actually predict there will be more. “You don’t have a clear theory to understand the number so it’s hard,” she says. Still, she notes that even with this uncertainty the models are predicting small changes in number, not big ones. “Even the ones that project increase or decrease are very small changes. Ten percent fewer. Small changes in the whole distribution. It’s not that we’re saying you’re changing from 90 to 0. Maybe we go up to 95 or maybe we go down to 85. That’s what we’re talking about.” But, she cautions, even if there are fewer storms, their intensity will increase, so fewer storms could still be able to cause more damage—especially if we don’t start adjusting our infrastructure and building practices (as we learned in the previous story in this series).
What We Don’t Know
There is a single study that the climate and hurricane scientific community is buzzing about right now and it’s one that we touched on in an earlier story in this series—the first comprehensive look at the speed of hurricanes over time seems to suggest that these storms are slowing down. “That is very new,” says Camargo. “Right now we just have one study. One study is saying it’s happening but we want to see more. Climate change could potentially be why, but there isn’t a study on that, so the link is not clear yet.”
One thing’s for sure, though—studying hurricanes is not easy and understanding their patterns and what makes them tick is a very active area of research. We have good models to help us predict the future, but the rarity of these storms (and the fact that we’ve only been able to see them from above for about 50 years) means there is still quite a bit of work to be done. Spotting trends, which is the key way that scientists determine the current impacts of climate change, is a tricky business.
“We don’t have enough hurricanes,” says Camargo. “It’s a rare event. Not having enough events and a long enough data set, it’s very hard to look at the trends and say ‘oh for sure this is happening.’” But she also says that, just because it’s hard to say what is happening right now, we can trust that our predictions of the future are solid. Our uncertainty about this moment “doesn't have anything to do with what we expect to happen in the future.” The warming planet is, without a doubt, changing our hurricanes.
