Monday, September 9, 2013

Where Are The Hurricanes?

No, I don’t mean my alma mater’s football team.  I am wondering why my Tropical Updates have been so quiet this year.  Not that I’m complaining, mind you (and well aware of the karma-tempting that talking about it may bring), but other people are also beginning to notice, Chris Mooney at Mother Jones included.

There’s no getting around it. We are very near the seasonal peak of hurricane season, and we have not yet logged a hurricane. That’s weird.

Indeed, the climatological peak for hurricane activity in the Atlantic Ocean is September 10, as you can see in this helpful image from the National Hurricane Center:

graphic depicting the seasonal occurrence of Atlantic hurricanes

Climatology of hurricanes, by date, in the Atlantic. National Hurricane Center

So what’s up with this year?

There are a variety of factors that are known to make for quiet Atlantic hurricane seasons—particularly the occurrence of El Nino conditions (as occurred in 2002) in the Pacific Ocean, characterized by very warm tropical ocean waters. But this isn’t an El Nino year. Meanwhile, other relevant phenomena currently out there in the atmosphere—a lot of dry air coming off the Sahara Desert, for instance, and a general sinking of air over the tropical Atlantic—don’t seem as if they, alone, can account for the lack of activity. “As air sinks, it compresses, warms, and dries out,” explains Jeff Masters—and that’s not generally conducive to the rising air of hurricanes. “But that doesn’t seem like it should be enough to explain why its been so quiet,” Masters continues.

The truth is that scientists and forecasters don’t really know what caused the lull during this season—which underscores the ongoing tentativeness of our understanding of what sparks individual hurricanes, and what causes their seasonal variability in general.

But just as one snowstorm in December doesn’t mean a wicked winter is a-coming, one slow hurricane season so far — remember, it lasts until the end of November — doesn’t mean that climate change is a hoax and we can all donate our canned foods to the homeless shelter early this year.

In the 1970s, when Congress was debating the safety of the proposed supersonic transport program, Maine Senator Edmund Muskie had just heard conflicting scientific testimony. “Will somebody find me a one-handed scientist?” Muskie allegedly exclaimed. That, at least, would put an end to all the “on the one hand, on the other hand.”

But we don’t need any amputations to figure out some things that we can indeed say about hurricanes and global warming. Principally this: While scientists sort all this out, sea levels continue to rise due to global warming. The picture here is very clear. And that means that every single hurricane that hits land will push seawater farther inland when it does so. Or as one scientist told me in the wake of Sandy, “There is 100 percent certainty that sea level rise made this worse. Period.”

And then there’s the warming of the oceans, which leads to two more clear conclusions, according to Masters. Warmer oceans make hurricane seasons longer, and they also make it possible for storms to travel north. The first idea is supported by published research suggesting an increasing frequency of late-season storms like Sandy (persisting into November or later), and the latter is simply a deduction from principles of physics: If oceans are hotter, hurricanes are more likely to be able to travel north out of the tropics and still have their energy source sustained.

And that, it seems fair to say, is more than enough to worry about.

Keep the tarps, plywood, and granola bars handy.