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How do hurricanes relate to climate change?

Mark Robinson

Saturday, April 26, 2014, 7:49 PM - Something crashed to the ground in the distance. The clatter and bang of it carried through the deep roar of the wind. 

I tucked myself into the dubious shelter of the stairwell as the rattle of debris echoed through the stairs. Bits and pieces of buildings skittered by, borne aloft in the howling winds. 

Hurricane Katrina was tearing Gulfport apart and we were in the middle of it.

Storms are often used to characterize climate change simply because they’re sexy. Statistics in a bunch of scientific papers just can’t compete with flying debris and blazing lightning. Unfortunately, they’re not that great as an example of climate. One off events like Katrina are interesting and amazing to see, but a single hurricane is not evidence for a change.

UNEARTHED: Catch Mark on T.V. on The Weather Network for the latest episode of his adventures in Antarctica, Sunday 7 p.m. and 10 p.m. EDT

Many people have pointed to Al Gore’s “An Inconvenient Truth” as evidence that the science is bad or has no idea what’s going to happen when it comes to climate. Storms make great TV and they tend to get people’s attention in a film, so of course, the producers opted to put in lots of footage of things getting blown apart. Unfortunately this led to an idea that hurricanes were a great indicator of climate change. To truly understand climate change, you have to look at the science and that means digging into the literature. Less sexy, but a lot more realistic.  

Hurricane Katrina was the most destructive hurricane to ever strike the United States and as it made landfall, winds were measured in the 240 kph range. A harbinger of what’s to come? Perhaps.  

When it comes to climate change, hurricane research can be split into two main areas; what’s happening now and what’s going to happen. Is there evidence that climate change is affecting storms now and can computers models show us what may happen in the future?  

Flooding in the wake of Katrina. Photo: United States Geological Survey.

Flooding in the wake of Katrina. Photo: United States Geological Survey.

Hurricanes are a relatively rare phenomenon despite the amount of media coverage that every single one gets whenever it even comes close to the US mainland. That means that the data is sparse and even worse, much of it is unreliable before satellite data gathering. 

However, there are ways around that. Digging into sediment cores from tropical islands, getting observations from ships, even historical records from the islands.

We can also equate sea surface temperatures with hurricane activity: the warmer the water, the greater the activity. The correlation between sea surface temperature and hurricane activity is very well known and very tight.  

So, combine these two indices and we can get a pretty good idea of how historical storms moved through the various oceans. And, we can answer the question: is there evidence that climate change has already had an effect on hurricanes? As always, let’s look at the science. The Geophysical Fluid Dynamics Laboratory, an organization with the U.S. National Oceanic and Atmospheric Administration (NOAA), is a prime research institution and they have been studying this for many years. 

They say simply that we simply can’t detect any evidence, so far, that there has been a significant effect. There is an upward trend in the number of hurricanes reported, but it’s more likely that the rise is due to observations getting better from the data sparse 1850’s to our ever-observant 21st century (you can take a detailed look at the study here).

So, the science says that there doesn’t seem to be a trend in storm numbers. What about the number making landfall? Back to the science we go and we quickly find that the same problem exists. Numbers seem to be rising, but when adjusted for observation bias, there is no significant increase or decrease in the number of storms hitting the US.  

So, the data tells us that the climatic warming we’ve seen so far has not had any detectable impact on tropical storms. However, that word detectable is important. Given the problems with the data that we’ve seen, it’s possible that there are trends that we haven’t (or can’t see) yet. 

But what about the future?

This is where modeling comes in. Researchers use highly complex computer simulations to try and determine if future trends will stay the same or if things will change.

The news isn’t great. Researchers check their models by using data that we’ve collected since 1980 (a reasonable point to assume that hurricanes are fully observed by satellite etc) to test out their model output. So far, the models are doing a very good job of simulating what’s already happened given the current climatic conditions. Once the warming we’ve observed in plugged in, things change quite a bit.  

Kerry Emanuel stated in a 2010 paper in Nature Geoscience that “the globally averaged intensity of tropical cyclones to shift towards stronger storms, with intensity increases of 2–11 per cent by 2100.” At the same time, the paper states, “Existing modeling studies also consistently project decreases in the globally averaged frequency of tropical cyclones, by 6–34 per cent.” 

Translation; fewer hurricanes but the ones that do get going are going to be stronger.

Image: Federal Emergency Management Agency

Image: Federal Emergency Management Agency

Why fewer hurricanes if things are getting warmer? Remember, it takes more than just warm water to sustain a hurricane. Wind shear, the change of speed and/or direction of the wind through the height of the atmosphere, is critical to maintain a storm. With little shear, hurricanes can get going and sustain themselves. With climate change affecting the way winds move across the Atlantic, it’s expected that shear will increase. This means that while there’s tremendous potential, not all hurricanes will get going.  

The big problem for hurricanes is that while there’s going to be more fuel for storms in the form of warmer oceans, an increase in wind shear over the Atlantic will destroy nascent storms.

All of this actually went through my mind as Katrina roared ashore over us. Gulfport was hammered by the hurricane and even as the storm began to fade northwards, its most punishing blow was striking New Orleans. The storm surge that the massive hurricane had created swept into Lake Pontchartrain and the levees protecting the city failed.  

Katrina alone might not be a good scientific example of the effects of climate change, but as these storms become stronger, this is the kind of effect that may become more common.  

So, what do we do now?

UNEARTHED: Catch Mark on T.V. on The Weather Network for the latest episode of his adventures in Antarctica, Sunday 7 p.m. and 10 p.m. EDT

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