Reader questions – Part 2 of 4


I recently received an email from Brittany C asking four questions.  Brittany is allowing me to publish her questions and my answers.  These answers are a combination of scientific fact with conjecture and opinion from me. Earlier, I answered the first of her 4 questions and today I will answer the second.

Question 2: If CO2 were linked to temperature increase wouldn’t that mean that temperatures would have steadily increased from the start of the Industrial Revolution to today?  If that’s the case, why was there a cooling period from the 1940s to the 1970s?

First, lets remember that there is no such thing as “steady” when it comes to the temperature or the weather.  The only things that steadily change are typically when we measure human influenced elements like the increase in CO2 that we discussed in the first question.

It is reasonable to assume that average temperature (in the inefficient manner that we record it) will fluctuate to new lows in any given increasing trend.  Weather is almost a perfect example of chaos theory so variations are expected but not always predicted.  That said, a period of 3 decades cannot be considered an outlying piece of data when considering our current data set of temperatures. This time period is often discussed by skeptics and was in the  film “The Great Global Warming Swindle” (as a point of clarification – I never saw this film but only read about it).

However, as important as this conversation on the drop in temperature may be, it is important point out that this drop was from an unusual high peak that occurred around 1940.  The average temperature had risen fairly dramatically from about 1900 to 1940 and when something moves dramatically one direction it is bound to rebound the other direction (unless it reaches a tipping point when chaos occurs).

So if we look at the temperature record more closely, we see that the temperature really didn’t drop from 1940 to 1970 but rather dropped rapidly from about 1940 to about 1950 and then slowly increased for the next 2 decades or so.  If it wasn’t for the rapid increase from about 1930 to 1940, the rise in temperature would have been quite steady.

So why did the temperature rise before 1940 and drop so quickly after 1940.  Unfortunately, this turns into a weather discussion more than a climate discussion with such a small timeframe.  Just like 2007 was reportedly very mild and 2008 appears to be quite cold, we cannot let the localized weather influence climatic discussions.  Several months ago, I chastised Laurie David for playing this card and I think it is poor taste for either side of the argument to engage in.

The most common theories on these changes are:

  • Sun activity
  • Volcano eruptions
  • Man made pollution
  • Divine intervention
  • Random fluctuation

Sun – The sunspot activity went through a down cycle at about the same time that the temperature dropped after 1940.  This cannot account for the entire change though since this cycle occurs ever 11 years.  It may have been a contributing factor combined with other events though.

Volcanoes – while probably not a significant factor as early as 1950, there were several volcano eruptions which added aerosols to the atmosphere and cooled the earth for a year or so. The most discussed volcano in the 30 year time period was Mt. Agung in 1963.

Pollution – The early 40s was a time of unprecedented increase in factory output.  This was the time of the second World War and goods were being manufactured at an amazing pace. This production spilled tons of aerosols into the atmosphere which, theoretically, would have resulted in a cooling.

Divine intervention – I am not going to give a lot of credence to this argument but there were quite a few people at that time that attributed the very rough winters as a divine deterrent to Germany’s aggressive plans. While I would never propose this as a scientific argument, I would be remiss if I discussed this period of time and didn’t mention it.  Sadly, many of this generation have passed on now, but it was a common belief at the time that the weather was fighting Nazi Germany.  Out of respect for a generation that sacrificed greatly, I mention it here.

Random – my personal feeling on a change that occurs in this short of time is that it is a chaotic mix of a large number of factors and that it is noise in the general discussion of climate. The average temperature increased about .2 degrees C in about 10 years and then promptly reversed itself in the next decade. I am very confident that if we had accurate global records for the last 500 years we would see the same occurrence many times.  It is only because our data sets are so small that this 20 year spike looks so powerful.

So as a short answer to the question, the temperature didn’t really drop from 1940 to 1970 as this is taking data out of context. The temperature actually increased from 1930 to 1970. This begins to get at the question that Brittany never asked but Pat Sajak did: What is the perfect temperature?

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1 thought on “Reader questions – Part 2 of 4”

  1. tim maguire says:

    Do you have any recommendations on where to find a good explanation of what global average temperature is and how it is determined? It is very difficult to believe that scientists have the slightest clue what the average global temperatures were before weather satellites came along.

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