Tuesday, July 16, 2013

1934 and other treasured legends of climate science deniers

Sou | 6:32 PM Go to the first of 2 comments. Add a comment

Climate science deniers have a few sacred legends that they are reluctant to relinquish.  They include the MWP - better known as the Medieval Warm Anomaly or Medieval Warm Period, the Little Ice Age and the dust bowl years in the USA.

Science deniers will rarely admit to the fact that evidence for the Medieval Warm Anomaly and the Little Ice Age relies a lot more on paleoclimatology than on pretty paintings or footnotes to historical documents.

The Medieval Warm Anomaly

As more data is collected and analysed it has become apparent that although the earth as a whole was most likely warm-ish, particularly in parts of the Northern Hemisphere, during medieval times, it was not the warmest period of the Holocene by a long shot.  When it was warm in one place it was cooler in other parts of the world.

Science deniers want to hang onto a myth that it was very warm everywhere.  As far as I can tell, this is because they want to argue "it wasn't CO2 in the past therefore it can't be CO2 now".  Readers here will immediately see the fallacy in this argument.  It's of the type: My car broke down but it wasn't because I ran out of petrol in the past so it can't be because I ran out of petrol now, even though the fuel gauge shows "empty"!  I think this is known as a Non-Sequitur. Maybe someone who is better versed in logic will agree or correct me here.

Here are a couple of charts of temperature reconstructions, which span the medieval period.  The first on is from Mann et al (2008) which shows the warmer period in the Northern Hemisphere during Medieval times.  It wasn't as warm as now, however.

Figure 3. Composite NH temperature reconstructions & published NH reconstructions from Mann ME et al (2008) Proxy-based reconstructions of hemispheric and global surface temperature variations over the past two millennia Proceedings of the National Academy of Sciences, Vol. 105, No. 36, pp. 13252-13257, September 9, 2008. doi:10.1073/pnas.0805721105

Update: At the request of Phil Clarke in the comments, here is a chart from Mann et al 2009, showing the likely global surface temperature anomalies from the 1961-1990 mean during the medieval warm anomaly. You can see where it was warm and where it was cold.  However, as urged further down in the section on the Little Ice Age, I recommend you read the paper before trying to interpret the chart.

Source: Mann et al (2009)

This next chart is from Marcott et al (2013), which is a temperature reconstruction of the entire Holocene.  The temperature anomalies for all the records are referenced to the 1961–1990 instrumental mean.  You can see the bump in the Medieval period.  However, from this chart it can be surmised that current temperatures are as high, or maybe already higher than even the Holocene Optimum and considerably higher than during the Medieval Period:
Source: Marcott et al (2013) A Reconstruction of Regional and Global Temperature for the Past 11,300 Years
Science 8 March 2013: Vol. 339 no. 6124 pp. 1198-1201 DOI: 10.1126/science.1228026

This next chart is based on the PAGES-2K project as discussed recently on ClimateProgress.  It doesn't show a clear Medieval "bump" in global temperature.  What it does demonstrate is that it is highly likely that the world is now considerably warmer than it was in medieval times:

Green dots show the 30-year average of the new PAGES 2k reconstruction. The red curve shows the global mean temperature, according HadCRUT4 data from 1850 onwards. In blue is the original hockey stick of Mann, Bradley and Hughes (1999 ) with its uncertainty range (light blue). Graph by Klaus Bitterman.
Source: ClimateProgress
You can read more about this work on realclimate.org.

1934 was a very hot year in the USA

Deniers from the USA are reluctant to accept that there are reasonably good instrumental records world-wide that can be used to determine global surface temperature anomalies in the 1930s.  They don't have to rely upon the many excellent photographs by Dorothea Lange or the memories of their grandparents.

Here is a chart of global surface temperature anomalies (GISTemp and HadCRUT4) showing the anomaly at 1934.  As always, click for larger version.

Data Sources: NASA and UK Met Office Hadley Centre

In 1934, the global surface temperature anomaly was below the 1951 to 1980 mean as shown in the chart above.

In this next chart you can see that yes, it was hot in the USA though not as hot as last year.

Data Source: NOAA

1934 was not such a hot year in Australia:

Data Source: BoM

And in Central England it was hot in 1934, but it's been hotter.  And it wasn't as hot as it has been lately:

Data Source: HadCET

The Little Ice Age

The reason science deniers promote the Little Ice Age is not that it shows that the climate was warm in the past :) No, it's because they argue that we are still "coming out of it".  In other words, they will try to argue that global temperatures are like a bouncing ball.  It does not require any 'forcing' to change.  What they argue is that global surface temperatures bounce up and down for no reason at all.  When temperatures drop they will bounce up again.  I've not yet seen anyone say for just quite how high or for how long the science illiterati expect it to keep on this upward bounce.

The "low" of the Little Ice Age can be seen in the Marcott chart above.  There is a paper by Mann et al (2009) in Science, which discusses the Little Ice Age (and the Medieval Warm Anomaly).  Here is a graphic from that paper showing the anomalies in the Little Ice Age compared to the 1961-1990 mean global surface temperatures.

Source: Mann et al (2009)

I'd urge you to read the paper before attempting to interpret the above chart.  I provide it to illustrate how scientists approach the science.  To show that scientists these days do not have to rely upon paintings by Brueghel to find out if the world was hotter or colder in the past.

Winterlandscape with skaters and bird trap Credit: Pieter Brueghel the Elder
Source: Wikimedia Commons

Climate scientists explore reasons for changes in climate.  They don't entertain hypotheses as simple as "temperature is a bouncing ball".  Rather they investigate what may have changed in regard to external forcings and/or internal variations that resulted in fluctuations in global surface temperature, precipitation patterns and other climatic features.

Fake skeptics dismiss the science out of hand.  They mock science and scientists.  For some of them it's because they value ignorance and despise knowledge.  For some of them it's just that they are unable to accept the fact that humans are altering the climate in a way that, on balance, is bringing great hardship and that there is worse to come.  Some are crank conspiracy theorists and distrust any source that they view as being connected to "authority".  Others have a vested interest in stopping the world from acting to limit the harm we are doing.  They are the ones who could be classed as amoral, sociopathic or immoral.  They prey upon and feed off the ignorance and fear of the 8% Dismissives.


  1. Yes, its a non-sequiteur, literally 'it does not follow'.
    Some examples of a few cool places during the MWP would be great, stop that talking point in its tracks....

    1. Thanks, Phil.

      As for the 'cool places', I've added a chart from Mann et al.

      I'm sure we haven't heard the last of this though. There will be more info to come as more proxies are collected and analysed, such as through the ongoing efforts of the PAGES-2K collaboration.


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