Hey, Tim Carney, Winters Aren't Getting Colder in Chicago

Last night's All In with Chris Hayes show included a debate about climate change between the host and conservative journalist Tim Carney.

They mostly talked about whether any single weather event can be ascribed to global warming or not. As is acknowledged by scientists, you generally can't say that a particular event was caused by global warming, from Superstorm Sandy to last year's drought in Texas to this week's wandering polar vortex. Hayes insisted, though, that these events illustrate what a warmed world will look like. Sounds reasonable to me, but then I believe the world is warming and we've got to do something about it.

Carney allowed that the world is warming and that greenhouse gases contribute to it. But he also said something I found hard to believe: That Chicago's winters are getting colder. He seemed to think this proved something important about the state of climate change.

Hayes did not challenge him on what sounded like a statement of fact, so I thought I would look into it.

The first impression you get is that Chicago's winters are and always have been fairly unpredictable. However, if their full-year mean temperatures are any indication, the winters are not colder.


Check out the bars from 1870 to 1990, for instance, and you'll see about half are above the overall average of 50 and half are below. Since 1990, though, only seven years have been below average, with only three of those since 2000.

The NOAA temperature records provide more data. None of the records for lowest temperatures are more recent than 20 years ago (it hit -21 in January 1994 … which is five degrees colder than their lowest low this week during the exaggerated polar vortex).

If you look at the numbers for the most consecutive days with a minimum temperature below zero degrees Fahrenheit -- one of those quality-of-life standards we're fond of here in Minnesota -- you won't find an upward trend over the past 20 years. The greatest spans on record are 10 days in 1912 and nine days in 1963. Since the year 2000, the average has been 2.3 days in a row, with a high of six (in 2000 and 2007) and a low of zero (last year). Doesn't sound like an upward trend.

So just how is Carney defining "colder"? If it doesn't include record lows or number of days in a row below zero or even total days below zero, what is it, and where is he getting his data?

Oh, I know. It must be average temperatures for the months December - February, right? That's better than data on record breakers. Okay.

So I finally found the seasonal mean temperatures for Chicago winters covering those months over 140 years and they don't support his point either.



The past five decades (starting with the winter of 1962-63) have had mean temperatures of 25.78, 24.08, 26.24, 27.6, and 26.38, respectively. Do you see a downward trend line there? (Especially when you compare it to the 140-year mean of 26.74.)

Nope. It just looks like normal weather variation in erratic Chicago.

Where did Carney get the idea winters were getting colder in Chicago? Who knows. But it's not true.
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If you'd like a copy of my Excel file (made from the NOAA data for the winter seasonal means), which is the source of the blue bar chart, send me an email.