So when does global warming get to Chicago?
Feb. 12, 2009

Dear Cecil:

Not a week goes by, it seems to me, that I don't hear about new evidence of global warming. The ice caps are melting, droughts and hurricanes are increasing, and now I see where the mountain pine beetle, no longer kept in check by now-mild Rocky Mountain winters, will soon wipe out the lodgepole pines of Colorado. Then I look out my office window here in Chicago, see what remains of the snow, and remember a month's worth of ice storms, subzero cold, and near-constant scraping and shoveling. Naturally I think: so when does global warming get here? Not that I would ever doubt Al Gore, or wish ill on the rest of the planet, but we could use a little of that global warming action, and so far I'm not seeing much. What gives?

— Charlie F., Evanston

Cecil replies:

Patience, Charlie. According to the latest research, global warming action aplenty is coming to the central Midwest, Chicago in particular. But I warn you: that doesn't necessarily mean it's going to get warm.

I call your attention to the above map, the handiwork of Noah Diffenbaugh, head of the Purdue Climate Change Research Center. (Here's a bigger version.) It appeared in a 2008 paper he coauthored entitled "Climate Change Hotspots in the United States." We'll get into the details in a bit, but first take a gander at the map, which purports to show how the contiguous U.S. and parts of Mexico and Canada will be affected by global warming by the end of this century. Colors on the left (low) end of the scale indicate regions that, relatively speaking, will get a pass, climate changewise. Colors on the right (high) end show areas that are going to catch it in the neck. Several things jump out at you, the most important of which from our standpoint are these: (a) things are going to be comparatively tranquil in the eastern half of the country, but (b) one of the exceptions is us. 

A few other general observations:

1. Bitch as you might about things locally, the part of the country that's really stands to get hammered is the southwest — and if there's one town squarely in the crosshairs, it's Los Angeles. Virtually all of the city and environs is in the red zone, and one sliver makes it all the way to indigo, meaning it'll show the highest responsiveness to climate change of anyplace in the lower 48.  An optimist, noting that the weather in LA is currently pretty nice, may think this merely means it'll get dramatically nicer. Realists, however, will point out that Los Angeles is already notorious for its wildfires, mudslides, blow-dryer-hot Santa Ana winds, and earthquakes. (OK, earthquakes aren't a weather-driven phenomenon, but surely they're indicative of the barely-in-control ethos at the heart of the LA experience.) I profess no expertise in these matters, but my guess is that on or about January 1, 2071, at the corner of Sycamore Drive and Brower Street in Simi Valley, California — ground zero of indigo land, by my reckoning — we'll see the opening of a portal direct to hell.

2. Speaking of 2071, you may wonder where a profession that can't reliably forecast the weather next week gets off predicting what's going to happen 62 years down the road. Presumably the operative philosophy is: one's reach should exceed one's grasp.

3. Then again, I note that among the regions predicted to be least affected by climate change, as indicated by dark green and blue on the map, are (a) the gulf coast, much of which was reduced to rubble by Hurricane Katrina, and (b) the state of Georgia, which is coming off a three-year drought. So, with all respect to the distinguished scientists who developed it, I wouldn't rule out the possibility that the climate-change modeling algorithm still has some bugs.

Back to that apparent hotspot around Chicago. I've studied Prof. Diffenbaugh's paper and spoken to him on the phone. Not to belabor the point, but hotspot doesn't mean hot. It means a region more likely than average to see change. Here I think Diffenbaugh's work has benefited from his having spent the past few years at Purdue. All midwesterners recognize the dramatic swings of climate to which the region is prone. If it's 110 degrees one day and 8 above zero the next, you may say on average the weather's nice. However, this statement glosses over significant nuances. Likewise, when the 2001 report from the Intergovernmental Panel on Climate Change says broad swaths of the U.S. will be slightly warmer and experience a little more precipitation than average in winter, the veteran midwesterner thinks: I bet there's a lot they're leaving out.

To deal with this problem, Diffenbaugh and his colleagues did a couple of shrewd things. First, they analyzed much finer-grained geographic detail than previous researchers, using a model that divided the country into a 25-kilometer grid. Next — and in my opinion this is the real breakthrough — they studied climate change not per year but per six-month season, April through September and October through March, lest offsetting changes in the two halves of the year cancel each other out. An impatient midwesterner who's had a spring picnic ruined by a sudden 25-degree drop may object: I'll be impressed when the climate-change timescale gets down to every fifteen minutes. I won't argue. But this is a start.

Anyway, here's a distillation of what Prof. Diffenbaugh had to say:

1. I'll assume you're getting that hotspot doesn't mean "place where it'll be hotter." Now wrap your head around this one: It may not mean mean "place where the weather will be more variable," either. It means "place where weather variability will likely be noticeably different from the way it is now." Since the midwest is already famous for sudden changes in weather, it's not out of the question that in the future the climate here will be less variable, and that it'll be 70 degrees ± 10 degrees every day, just like in LA.

2. But don't hold your breath. Diffenbaugh says the midwestern hotspot is shaped mainly by year-to-year temperature variability in the cold months, with some contribution from precipitation variability in the warm months. I'll go out on a limb and guess this means more summer droughts, plus winters that are mild some years but other years a bitch.

3. That said, the rougher-than-usual winter we're having just now doesn't prove anything. The midwestern hotspot doesn't show up in Diffenbaugh's maps until 2071 — there's no sign of it in earlier decades. "This raises some question about how robust the midwest hotspot is," he says. In contrast, the southwest hotspot — or hot zone, since it covers a huge area — shows up in most maps from 2011 on out, regardless of methodology. So if beetles kill all the lodgepole pines due to higher temperatures, I figure you're not taking too much of a flyer if you attribute this to global warming. Whereas if you get flattened by an ice storm in Chicago, that just means the weather here sucks.

4. Lest you take any comfort in the thought that, while things may not get dramatically better in the eastern half of the country, at least they won't get dramatically worse, you should know that Diffenbaugh's analysis doesn't pick up transitory phenomena such as storms. Thus if you live on the gulf coast, current science says the changes in your weather will be relatively modest. Except possibly for the weekly hurricanes.

5. If you're wondering what's in store for Los Angeles, the big change looks to be greater dry-season variability. Remembering the adage "it never rains in California but it pours," I surmise that means God's own nightmare of wildfires and mudslides. On the other hand, temperaturewise it'll be warm and probably warmer, so you'll still be able to watch all this dressed in shorts.

6. Prof. Diffenbaugh was a bit tetchy on the subject of the reliability of long-term climate projections, pointing out that the models have accurately predicted climate change up to this point. We'll see. I'll be a little creaky in 2071, but you can bundle me up and wheel me out to the lakefront anyway. If there's nothing to be seen but a mud flat, fine, that's global warming. On the other hand, if we observe blizzards, tsunamis, arctic cold, and so on … well, doubtless some will see that as evidence of increased climate variability. But Chicagoans with long memories are likelier to think: eh, more of the same old same old. 

— Cecil Adams

References

Diffenbaugh, N. S., F. Giorgi, and J. S. Pal (2008), "Climate change hotspots in the United States," Geophysical Research Letters (2008), v. 35, L16709: http://www.purdue.edu/eas/earthsystem/Diffenbaugh_GRL_08.pdf

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