Thursday, November 1, 2012

Sandy Rides the Atmospheric River: Climate Change and the Monster Storm

Even though Sandy's remnants are still spinning down and the Midatlantic is only beginning its cleanup from the storm, people are already starting to talk about whether or not human-caused climate change may have created or worsened the storm.  I'm not going to cover the topic in depth, but there are a few things worthy of mention here.

First of all, Sandy was a huge storm, a monster created when a hurricane merged with an extratropical storm.  This scenario can lead to some of the largest and most intense storms our planet can experience - storms that combine the hot, wet tropical energy of a hurricane with the battling air masses of the mid latitudes.

This is not the first time such a storm has formed.  They have ranged in the Atlantic and the Pacific before, and as far as I know can occur in the Southern Hemisphere as well.  Sandy was a monster, but was it our creation?  Not necessarily.  Sandy passed over the warm Gulf Stream, which is warmer than usual right now, and this may have strengthened the storm a bit.  But even without this factor, Sandy would have been a very severe storm.

There's more, though.  A monster isn't defined just by what it is, but what it DOES.  Extratropical storms, even the huge ones, almost always move from west to east.  Had Sandy curved to the east, like so many other storms, it would have spent its wrath over the ocean.  Perhaps Sandy would have hit Newfoundland like the Perfect Storm, or could have crossed the ocean and hit Europe, but at that time the storm probably would have been weaker.

Sandy, on the other hand, turned west.  This was surprisingly well-forecast by computer models, and was caused by a deep meander in the atmospheric river we call the jet stream.  Erratic hurricane paths are not uncommon, and the 1938 hurricane followed a somewhat similar one.  The jet stream pattern was nevertheless quite unusual.  It's one we've seen before, though.  I wrote about it almost two years ago in the second most viewed post on this blog.  Lack of Arctic sea ice may make that weather pattern more common.

The quick summary?  The jet stream rotates around the North Pole both because of the Coreolis Effect and because the North Pole is the coldest spot in the hemisphere... or at least it was.  For most of the last few centuries (and perhaps since the last Ice Age) the Arctic Ocean has been frozen.  The thick ice allowed the air to become incredibly frigid.  Lately there has been very little sea ice.  Liquid is an incredible moderator of temperature, and an Arctic Ocean with open water tends to moderate the winter temperatures upwards towards the freezing point, because it can't get more than a few degrees below freezing (salt, of course, decreases the freezing temperature of water).  The Arctic Ocean is then perhaps less cold than Canada, Siberia, and Greenland.  So, the jet stream shifts south around those continents, and orbits around the new 'poles of cold' in the continental center.  This could lead to increased wandering in the atmospheric river... the kind that could grab a monster from the Atlantic and pull it right into the most populated part of the Eastern US coastline.

Jeff Masters does a good job of describing this in more detail here.

This is all new science of course.  We don't know anything for sure.  It's a bit scary though.

The hurricane season is winding down so we probably won't have to worry about any more hurricanes being ingested by nor'easters this year.  The pattern may, however, lead to a brutal winter in the Northeast this year.  Less sea ice doesn't warm New England all that much, it will still be plenty cold enough to snow, and we may have to deal with more storms than usual.

Or maybe not.  Last winter was a non-event here.

What do you think?  I'd love to hear any thoughts on the science and what the future may hold.  Please keep to the science though.  I know people like to argue about global warming on the Internet, and it's fine to have a debate if you can back up your claims, but I'm gonna delete any 'GLOBAL WARMING IS A LIBERAL HOAX' posts, or anything about HAARP or chemtrails (if you don't know, don't ask. You don't want to know.)

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