Is global warming making hurricanes worse?

Answer

There is no simple answer to this question. That is partly because you have to define what you mean by “worse.” You might be asking whether we are seeing more hurricanes than we did in the past. Or you might be asking if individual hurricanes are getting stronger. Or you might be asking if we are seeing more damage from hurricanes.

Then, once you know what the question really is, you have to figure out what role climate change might be playing in each of these.

At the most basic level, most hurricane experts agree that warming ocean waters should, on average, make hurricanes more powerful. That’s because hurricanes get their energy from the evaporation of seawater — and seawater evaporates more easily when it’s warmer.

It is for this reason that the Intergovernmental Panel on Climate Change, or IPCC, the most authoritative climate-change group in the world, projects that there will be a “likely increase in tropical cyclone intensity” for the coming century, thanks to human-caused global warming. (The term hurricane is only used for Atlantic storms; tropical cyclone covers hurricane-like storms in all parts of the world).

Is it already happening? Possibly. There are hints in the data that suggest an increase in the number of hurricanes in the North Atlantic over the past few decades. The evidence is better for an increase in hurricane intensity. But in both cases, more data are needed before scientists can be certain.

Beyond that, while most climate models predict that the strongest tropical cyclones will get stronger as human-caused global warming continues (that’s why the word likely in the IPCC’s statement), some models suggest that the number of storms may not increase. Many factors influence the formation of hurricanes and tropical cyclones, including wind patterns, ocean currents, and local weather conditions. All of these may change in a warming world, in ways scientists are not yet certain of. So it is really hard to project how the numbers will change worldwide. There could be more hurricanes and tropical storms in the future. Or there could actually be fewer. This is a difficult problem and more data and research are needed.

If we are talking about damage, though, everyone agrees that it will get worse. Part of that will be due to global warming. Warming makes sea level higher, which means the kind of storm surges that devastated New Orleans during Hurricane Katrina will have a head start.

But a more important factor in the near term is likely to be population growth in low-lying countries like Bangladesh and near seacoasts in places like Florida, Texas, and Louisiana. We have already seen that kind of growth over the past couple of decades, putting tens or even hundreds of millions more people in harm’s way. Even a relatively mild hurricane can kill more people and destroy more property than the most powerful storm could have 50 years ago. So while Hurricane Katrina, for example, was the most damaging storm to hit the US on record, it was not the most powerful. It just happened to strike a major population center whose hurricane-protection system was not up to the job.