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Comparing Temperatures With 2001/2

August 25, 2013

By Paul Homewood




As regular readers will be aware, I have recently been making comparisons of current global temperatures with those of 2001/2.

Why? Global temperatures can fluctuate year by year with changes in ENSO conditions, and this can make direct comparisons and estimation of trends difficult. The Hadcrut temperatures above, for instance, show spikes during the El Ninos of 1997/8, 2007/8 and 2009/10. Equally, there were drops during the La Ninas in 1999/2000, 2007/8 and 2010/11.

These ENSO changes can be seen on NOAA’s graph below.




In fact, until the last few months, the last longish period of ENSO neutral conditions was from April 2001-March 2002. Currently, ENSO has been running around neutral since last September, so we should be able to make some meaningful comparisons of temperatures. See here.

It is generally accepted that there is a lag of about 3 to 6 months between changes in ENSO, and their effect on temperatures. Trenberth, for instance, goes for 3 months, but also acknowledges that others prefer 6 months.

So let’s run with both.


3-Month Lag

Figure 1 plots the Hadcrut4 temperatures for July 2001-June 2002, i.e. allowing for a 3-month lag after ENSO turned neutral in April 2001. The average temperature anomaly during this period was 0.51C.



Figure 1


Now let’s compare this with recent temperatures, since December 2012, 3 months after last summer’s El Nino fizzled out.



Figure 2


The average since last December has been 0.44C. In other words, under similar ENSO conditions, temperatures in recent months have been running lower than 2001/2.


6-Month Lag

Now let’s assume a 6-month lag.


Figure 3



Figure 4


The average for October 2001-September 2002 was 0.51C, while the current year is running at 0.46C. So, whichever assumptions about lag we use, temperatures during the recent period have been lower than 2001/2.



So what can we draw from all this?

1) While there are many other factors that affect global temperatures, we can say that, under similar ENSO conditions, temperatures currently are slightly lower than 11 years ago.

2) The current period is still not a long one, and we should get a better picture if ENSO remains neutral over the rest of the year.

3) It must also be remembered that ENSO is an integral part of the climate, and cannot just be simply dismissed as a variation to be ignored. Nevertheless, it does emphasise just how flat temperatures have really been in the last decade.

  1. Brian H permalink
    August 25, 2013 6:41 pm

    ‘Flatter-y will get you … everywhere.’

    Is this a new ‘base’ for the El Nino Southern Oscillation, then?

  2. Terbreugghen permalink
    August 25, 2013 6:43 pm

    Paul: Can you briefly explain the difference between temperature and temperature anomaly? While your title implies a comparison of temperature, the graphs you’re showing cite temperature anomalies, which are different than raw temperature measurements. Many thanks in advance. (If I understand the graph correctly, the temperature anomalies indicated by the graphs are the degrees above some conventional mean. While temperature anomalies may be below the average for the periods measured, it would seem they are still above that conventional mean. Finally, what IS that conventional mean, and how is it derived?)

    • August 25, 2013 10:16 pm

      Thanks for the question.

      It’s worth doing a post on tomorrow.

  3. August 28, 2013 8:45 pm

    We’re currently at solar max. What was the situation in 2001/2002 ?

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