Months since below average temperatures

NOAA have recently been promoting that November 2012 was the 333rd month in a row with above average global temperatures, and this has been widely picked up by the media (e.g. here). But, how useful is this statistic?

Firstly, this statistic uses the global mean temperature from one dataset (GHCN v3.2.0), and assumes that “average” is the whole of the 20th century. The answers would vary slightly when using a different dataset, but the choice of average period is key. The 20th century is an arbitrary choice (as is any such choice) – a smaller number of months would be found if a more recent averaging period such as 1961-1990 or 1986-2005 was used instead. So, the number of months depends entirely on an arbitrary choice, which ensures the statistic is far from robust.

Secondly, but far more importantly in my view, this global statistic does not match how people experience climate, which is on the local scale, mainly by looking out of the window. Recent work suggests that “people can perceive and adapt to aspects of climate variability and change based on personal observations“. My personal experience matches this.

Below, the same NOAA data and averaging period is used, but now presented regionally, and shows how many months since a below average month in each available grid cell, i.e. locally. The picture is very different with the majority of regions having a cooler than average month within the past 2 years, and for many regions it is less than 3 months. Interestingly there are slightly larger numbers in the tropics, perhaps because the variability tends to be smaller there.

This type of global statistic is damaging, precisely because it does not tally with how people experience climate change and variability. Much better to take the opportunity to educate and increase understanding about how the climate varies from year to year.

[Many thanks to Doug McNeall, John Kennedy & Scott Mandia for useful discussions.]

Months since below average temperatures
Number of months since below 20th century average temperatures for that particular month.

About Ed Hawkins

Climate scientist in the National Centre for Atmospheric Science (NCAS) at the University of Reading. IPCC AR5 Contributing Author. Can be found on twitter too: @ed_hawkins

9 thoughts on “Months since below average temperatures

  1. Hi Ed,

    To me, such statistics seem to fall foul of what is intuitive. What determines a long run of positive anomalies to a yet to have happened norm?

    Just regarding the global record for what it is worth:

    Should the globe have not much warmed after 1946 but had also not cooled either, perhaps a run starting in the 1930s could have persisted for a longer interval, only to evaporate, retrospectively cease to be, should strong warming occur in the last decade or two.

    Should the months warmed by the 1997/8 El Nino have been more moderate perhaps the run would have stretched back further as the norm would have been cooler.

    Should the last decade of the last millenium and the time since have been a lot hotter, the run would surely risk being shorter due to the norm for the past centruy being warmer.

    There seems a real risk that well timed moderation would have made for a longer record.

    I suspect that there be a critical late 20th Century trend that would maximise this statistic, with both more and less warming making the run shorter. Some relationship between the slope of the trend, its start date, and the monthly fluctuations.

    I am not sure whose attention that statistic is meant to entertain. It seems to be aimed awfully low down the scale of things, to the point of an insistence that the globe warmed during the last part of the 20th Century to gainsay those that might insist that it didn’t.

    As you point out we are for the most part rather well localised. Exceptions being those who make roving science/nature documentaries and the scientists who preceed and follow such trails.

    We are also fairly well located in time and there can be few for whom the chilly start to the 20th Century adds to a meaningful comparison.

    In terms of how events, directly experienced, colour our perceptions, the valleys of the Indus, Nile, Ganges, Yangtze, etc., must weigh more heavily than those by the denizens of the Antartic Peninsular.

    The Armstrong & Miller clip is hilariously funny, very entertaining, yet it might be hard to fathom out why. In marketting terms I suspect it would be judged to be very effective. What is not to like?

    Very little is said about UK climate legislation, what it is and how it came about. It was a localised occurence, built on local events, local activism, local weather, and local politics. I think it needs to be considered along side other movements towards localism. The Climate Act made hay whilst the sun shone. Getting it written and enacted was in a strong sense a coup de environment.

    I did read the Act with the reaction “Wow”. It is quite startlingly in its depth and scope. So why is it, and why not similar elsewhere? I rarely, almost never, see anyone address the anomaly of the political climate of the UK away from the global norm.


  2. I beg to disagree. The beauty of the 333 month statistic is that everyone understands it instantly and it is a measure of precisely the issue at hand. ‘Local warming’ is not a global problem demanding global action. The proportion of people who could understand your elegant 2D graphic in less than 5 minutes is woefully small, judging from my experience. The fact that the reference period was missing from most headlines on the 333 month stat, rendering it meaningless in a scientific sense (but not in a public communication sense) simply illustrates the gulf of scientific rigour missing from your target audience, and how completely they would fail to understand the regional graphic. Nice analysis for the initiated, however.

    1. Thanks for the comment Neil! Firstly, I would certainly not advocate the regional graphic for general public communication – I agree that it is probably too complicated. But, the 333 month statistic seems, to me, to be too open for (some) people to say, ‘well, not where I live’ and then dismiss it. I think there are better ways of communicating that the world has warmed, but that it does so unevenly – I particularly like the Armstrong & Miller video sketch linked to in the post. I think the unevenness of the warming is very important to communicate at the moment given the slower rate of warming of the past ~15 years.

      I guess it also depends on the aim of the communication and the target audience. The ‘public’ are, of course, actually a very broad range of publics, and perhaps the 333 month statistic will be helpful for some, but the slightly more educated will easily point at the fairly obvious holes in the statistic.


    2. Neil,

      Now you might be Dr Neil Edwards (OU), you might not, in either case you seem to look down from a great height, and feel free to insult and denigrate, those to whom appropriate ideas shall be communicated.

      We, who are lowly, are well localised, in time and space, yet familiar with the greenhouse effect at least as far as having heard of it and its implications for warming. Some, I included, without any specific training, have disseminated the core idea for many decades and have watched our locale for hints and clues, occassionally muttering to the effect “It bain’t right y’ know”.

      We have influenced legislation, which is a local jurisdiction, and it was well done. I would be hard pressed to tell what prejudices were at work, maybe it were some statistical relationships of a global nature or the plight of the sand eels.

      Here is an extract from a teaching resource aimed at students from KS2 upwards:

      “Threats [related to sand eels]

      Seabirds, whales and other marine animals may be finding it difficult to find the food they need to survive. This shortage may be caused by a rise in sea temperature brought about by climate change, which allows different zooplankton species – which sand eels do not eat – to move in. This is reducing the numbers of sand eels or causing them to move away. Over fishing also makes the situation worse.”


      Now some think that students from a young age can grapple with such ideas (given sufficient support). It is quite a sophisiticated multifaceted argument, with relationships from the specific to the general with multiple causations. Alternatively, some seem to think the plebian and pagan be simply beyond the pale that girds the initiate. Those I caution lest “Hang yourself, Brave Crillon!” be the cry.

      Do you believe in magic, so many seem to, and seek the Sangrael for the bullet that transforms all things. Whilst others look to the small and its power to modify, to harness, and to tame. A nation of nations that has rebuilt itself to be post-imperial, post-industrial, will be post-carbon in the same degree, if that be in the commonweal, expressed as the common will, or by the more prosaic determination to bow to necessity as in the early cases.

      Should I understand, which I don’t, the meaning of your 333 month stat, I might ask as to “What I can do to get it down to a more reasonable 100 month value?”

      Answer please.


  3. Alex

    Good question, but it sounds like you are doing all anyone can be expected to do already. As for understanding, it is almost always a matter of time, interest and prior knowledge, almost never ability, otherwise @OpenUniversity would not have been the instant success that it was. Lack of it should therefore be seen as an invitation to learn, rather than an insult.

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