Global Temperatures: Month of December

I have discussed the difference in the global temperature and the global anomaly before.  The most interesting part of that discussion is the observation that different months of the year have different behavior.  The Northern Hemisphere (NH) winter months have more variation year to year than the summer months do.  That means during the winter there is a bigger difference between mild winters and cold winters.  The summer is more consistent year to year.

Looking at the trend for a single month can sometimes show surprising results.  For instance, let’s take a look at the month of December.  Over the past 150 years it has seen a very large range in temperatures.  Here is the December global temperatures from 1850-2009.

The Inconvenient Skeptic

Temperature for the month of December from the Blended set

There are some interesting pieces of information in this chart.  In the 1850’s there were 2 of the warmest Decembers over the entire period.  The 1850’s also had some of the coldest Decembers.  There is almost a 2.0 °C difference between the winters in the 1850’s.  The average temperature was slightly below the zero anomaly, but there were huge swings in temperature.

The moving average dropped almost 0.5 °C into the 1860’s.  The big difference was the 1860’s didn’t have any warm Decembers.  That was enough to drop the average of the decade 0.15 °C.  The 1870’s had some warm months again, just not as warm as the 1850’s.  It wasn’t until the 1930’s that the December temperatures again climbed near the warm December averages that the 1850’s experienced.  Since the 1930’s didn’t have the cold winters to average out the warmth, the average temperature was 0.25 °C higher.  The maximum temperatures were lower, but the average temperature was higher.

Even in the past 10 years what is apparent is not temperatures that are shockingly higher, but there are less very cold temperatures.  1933 was the last year that December had an anomaly temperature that was below -0.5 °C.  Over the entire period the average standard deviation for the month of December is 0.34 °C, although the biggest change is that the standard deviation has been shrinking.  The month of December may look warmer, but really what has happened is that there as been less very cold Decembers.  3 of the 5 warmest months happened more than 70 years ago, with 2 of the warmest taking place in the 1850’s.  Part of that is the nature of the blended data, but as the data gets more accurate the error decreases.  Certainly the modern day satellite data is far more accurate than the piecemeal records from the 1850’s.

For the past 160 years the month of December has shown periods with warm winters in the 1850’s, 1930-1940’s and now again since the mid 1990’s.  The most unusual difference is the recent lack of very cold Decembers, but that has happened before during the 1930-1940 period when there was a long period of warm Decembers then.  It will be interesting to see how this December turns out.

The Inconvenient Skeptic

Lolo Pass

Posted in Anomaly by inconvenientskeptic on December 14th, 2010 at 11:15 pm.


This post has 2 comments

  1. 4TimesAYear Feb 16th 2011

    I’m sorry – this isn’t really about December’s temps – it was your use of “global temperatures” that grabbed my attention. I have to say that some years ago it occurred to me that a “global temperature” was something that couldn’t possibly exist. After doing some research, I found there were some brilliant minds that had reached the same conclusion – of course there’s no such thing – it’s an “average global temperature” but even that’s really meaningless since an “average” doesn’t melt anything, nor does it tell us anything about what the real temps were. (In fact, averages can be downright misleading – for example, the average for a day where the temp hovers at 71-72 all day will be higher than for a day with a high of 80 and a low of 60; the average doesn’t tell us what the temp was on either day, it especially doesn’t tell us which day was warmer)
    I just discovered your blog, so I’m not certain if you’ve ever addressed the subject; if not, perhaps you might be interested in a few links on the subject:)

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