Last Three Decembers below Average in the United States

The United States has experienced three Decembers in a row that had below average temperatures according to the GHCN (NCDC).  The last time this happened was the period from 1966-1968.  While the overall temperatures have not been exceptionally cold (the coldest was the 14th coldest on record), the string of below average Decembers is unusual.  The last time there were four below average Decembers was 1924-1927.  This gives next year the chance to really set a significant record string of below average temperatures for the month of December.

Of course this is the GHCN station data which is on average warmer than the satellite records.  It is no surprise that they already give the US a 4 year string of below average temperatures for December.  So depending on the source of the temperature data the month of December has been below average for the past 3-4 years.

The GHCN data has the actual temperature for US as well as the anomaly.  The average temperature for the month of December in the US is 33.38 °F (0.767 °C).  Here is the full set of data for the month of December.  I also included the 3-year moving average.

The Inconvenient Skeptic

US temperature for the month of December. Average temperature is slightly above freezing at 0.767 °C.

The 3-year average is now well below average and lower than it has been since 1989.  Since it is often claimed that Global Warming will cause winters to be warmer before causing the summer months to warm, it would seem that the trend in the United States indicates that it hasn’t yet arrived.

There are two aspects of this chart that really interest me.  First is that there have always been very warm Decembers as far back as the records go.  1939 was by far the warmest December in US history at a much above average 38.48 °F (3.6 °C).  That is 5 °F warmer than the past December.  The period from 1939-1941 all had average temperatures that were more than 3 °F warmer than the past 3 years.  Once again the past shows that such variation, warm and cold, is normal.

That is what this chart shows the most clearly.  The temperature on any given year can be well above or below the average.  Despite all the noise around the average, not once does a trend mean anything.  Series of warm or cold are always followed by the opposite.  The trend is different for every group of years that are analyzed.

115 year trend = 0.12 °F/decade

100 year trend = 0.10 °F/decade

75 year trend  = -0.05 °F/decade

12 year trend = -2.6 °F/decade

So which trend is correct?  None of them is useful in predicting the future temperature trends, so in that respect the trends are meaningless.  So are any predictions of the future that are based on the temperature trends.  Predicting the future on a trend line is simply a waste of time and always misleading.  Maybe that is why they are so often used?

Posted in Anomaly by inconvenientskeptic on February 1st, 2011 at 3:27 pm.

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