Friday, November 27, 2009

Freezing earlier in a warming world

A friend jabbed me with a comment that in spite of the early cold elsewhere in the country, Dallas had not yet had a freeze (this was on Nov 22, I don't know when this blog will be published). I downloaded the data for a small town just west of Dallas/Fort Worth, Weatherford Texas and calculated the first day of each Fall in which the minimum temperature fell below zero. Since people aren't generally running air conditioners on days that freeze, the thermometers will not be affected in the same way as the high temperatures, which happen in summers.

So, what does Weatherford look like? Look for yourself.

Over the past century, Weatherford, Texas has had its first Fall freeze earlier and earlier (smaller Julian Day number which is simply the number of day in the year this day is) This is not what one expects in a warming world.

Another friend, after telling him about this, said that I should look at the last freeze in the springtime. That is the picture below. You can clearly see that over the past century the last freeze of the year has come later and later (higher Julian day number), meaning that the time between the first and last freeze has been growing.

So, lets put both curves together. I added the days from the first freeze of the winter until the end of the year to the Julian day of the last freeze. If the trend is getting bigger, then wintertime is growing. If it is getting smaller, then wintertime is shrinking.

Since I wrote the above (but before I published this), my friend who started this look at the data sent me a link to some Dallas-Fort Worth winter temperature data at the National Weather Servicehere. I plotted the number of freezing days each winter in Dallas and then calculated the trend. The trend is flat (technically slightly more freezing days now than 100 years ago, but that isn't what one expects in a warming world that is about to all die from the heat.

Clearly winters are getting longer. Do you expect this in a warming world???? I don't.

Because I was surprised at this, I looked at Riverton, Wyoming, a place I began my geophysical career in, working on a seismic crew up there. One would expect that Riverton would warm and that would push back the day of first freeze. If I use all the data with the first freeze past Mid July, the data looks like this:

Riverton is just barely warming, not quite what I expect given that we have 1/3 more CO2 in the atmosphere than we had in 1907. But look at that one day in 1912. That was an early August freeze, Aug 7. 1912.

What is the significance of that day? Well, two months earlier the 20th century's most powerful volcanic eruption had occurred at Katmai, Alaska, on June 6, 1912 (source). Volcanoes, it is known, drop the planetary temperature rather quickly. I would guess that that single freeze is probably related to it. But even if it isn't, lets see what removing that day does to the trend of first freezes. That is below.

Without that one day, Riverton is actually cooling, with the first freeze coming slightly earlier each year over the past century. Clearly this isn't what one would expect listening to all the hysteriacs baying at the moon.


  1. Are you drawing the trend lines with least squares? If not how?

  2. I am using Excel's slope and intercept functions. Here is what the equation says, assuming it posts.

    The equation for the slope of the regression line is:

    b= sum ((x-x_bar)(y-y_bar))/sum(x-x_bar)^2

    where x and y are the sample means AVERAGE(known_x’s) and AVERAGE(known_y’s).

  3. AFAIK that looks like least squares. The variation seems large compared to the steepest slope in the graphs shown but Weatherford appears to be getting longer winters which is counter intuitive under GW assumptions.

    In the 80s I used to ski with a friend in Vermont. As we drove home and got close to Toronto it was constantly necessary to reduce the thermostat setting in the car as we got too warm. The latitude is close to the same and for most of the way we drove on the north shore of Lake Ontario. Thus the winter heat island effect is quite pronounced.

    Dave W

  4. IT’S autumn, and the people on the Chuo Line are all bundled up, just as they are in the spring. When I was a student, a friend from Hokkaido, in the north, told me she couldn’t stand the winter cold in Tokyo. Although the temperature is lower in northern Japan, in Tokyo there is no moisture in the winter air; the dry winds bounce off the buildings, picking up speed until they seem to cut into your skin, making the cold intolerable.

    Tokyo warmer winters?
    When I was in elementary school in the mid-1960s, there were still paddy fields and vegetable patches on the outskirts of Tokyo. On frosty winter mornings spears of frozen grass crunched under my shoes as I walked to school, and it often snowed. Winters were harsher than they are now, but the face of spring was more clearly defined, boldly announcing its arrival.

    Could be heat island effect? Getting some records and making a plot like above would be interesting both for Toyko itself and a nearby rural spot. In Toronto the heat island effect used to extend about 25 miles east and west from the down town core.

  5. Those are very interesting pieces of information Dave. I will see what I can find around Tokyo