- The Dubious Significance of Trends in Global Mean Temperature
- Early attempts to Chart Global Climate Variation
- Global Mean Temperature Charts published after 1950
This page is an ongoing project to track the history of the scientific assessments of global temperature change over various post-glacial time periods. Thus the title is best given as NOTES TOWARDS…
The History of Global Mean Temperature Charts
Any scientific prognosis is alway grounded in observation of present and past conditions. This is no exception for Climate Change Science. And when it comes to the predictions of unprecedented and runaway global warming, the graphic presentation of time-series of collated observed temperature data has always been important for supporting this claim. However, the relationship between the charting of global temperature trends and the warming alarm has not always been harmonious.
The IPCC First Assessment of 1990, and its supplement in 1992, actually went as far as to say that the evidence, both from proxies and from recent instrumental records, presented no cause for alarm. Rhythmic fluctuations were noted on a range of time scales, and the recent warming was not assessed as outside these normal fluctuation. This assessment of the evidence was part of the reason why the 1992 Supplementary Report, prepared especially for the Rio Earth Summit, concluded soberly that it is still not possible to attribute with high confidence all, or even a large part of, the observed global warming to [the anthropogenic enhancement of] the greenhouse effect.
The lead-up to Kyoto was quite a different story. It was the late changes to the Second Assessment—so that it proclaimed scientific evidence of recent human-caused warming—that generated an unbearable tension between the scientific observations and the proclaimed official scientific ‘consensus’ on the matter (see more on the Chapter 8 Controversy). To some extent this tension was already eased by contracting the historical view back from the millennial time-frame. By charting from 1400 (after the Medieval Warming) the ‘unprecedented’ claim was easier to make.
But then with the IPCC Third Assessment dramatic changes were introduced at the level of evidence. In 1998 the first version of the Hockey Stick graph had appeared in Nature before another version was headlined in the release of the Third Assessment Report. Take one look and there was now no doubt about the unprecedented and runaway nature of recent warming. And all sorts of version of it appeared, including the one above, with the error bars on the proxy data (the shaft) removed and the blade of grafted instrumental temperature extended continuous with the worst-case model predictions of future warming.
The Fourth Assessment of 2007 includes another graph, this time derived only from the recent instrument records, and it tells the same unprecedented, and runaway story . Despite the dubious analysis it presents, the president of the IPCC was still headlining it at the Copenhagen Conference in December 2009 (see Monckton’s analysis here). These graphic presentations of mean temperature—with all the scientific authority they have invested—have proved very persuasive tools in generating alarm in the community. And so on this page we follow the evolution of global temperature graphs through the history of Climate Change Science in order to determine to what extent they drive, or are driven by, the prevailing alarmism of the authors and the times. But before we do this, it is important to put them in perspective; to firstly determine what they are measuring, and how significant are the trends they apparently express.
2. The Dubious Significance of Trends in Global Mean Temperature
From a systematic viewpoint the mean temperature of the atmosphere near the surface of the earth is both difficult to determine and difficult to defend as an indicator of the thermal state of the climatic systems: there is constant vertical movement of the air due precisely to warming and cooling; moist air contains more heat then dry air of the same temperature, and so temperature is a poor indicator of heat content; and then the oceans are the true heat bank, receiving much of their warmth directly radiated from the sun, which they then giving off to the atmosphere at varying rates.When a location or region has an extraordinarily warm winter or mild summer or etc…, the anomaly is usually reported as 2 or 3 or more degrees Celsius/Kelvin from a previous norm. Such variations have a noticeable effect on human comfort, agriculture and the natural world—especially if they persist in a trend over a number of years. Just such trends are found in various locations across the globe attributable to nature and human causes. One of the most common such climatic change occurs in expanding cities. If a similar scale trend were to occur in the global average temperature we would certainly know about it, for it would have enormous impacts on human civilisation. Yet there is no suggestion a variation of this magnitude has occurred even across the last century or two. Remarkably it seems that all the local anomalies that occur every day, month and year, all the great heatwaves, droughts, cold snaps and blizzards, seem to more or less cancel each other out every month and every year such that if the data for global mean temperature were rounded to the nearest degree then there would not be much to show.
This is why graphs used to demonstrate global warming are usually calibrated in tenths of a degree, with values plotting to 1/100oK. The range of variation, the range of error and level of adjustment required to cover all sorts of inconsistencies in the data make it hard to justify such precision. Richard Lindzen demonstrates the absurdity of fussing over reported warming of less than a degree in a number of recent presentations (including here and here).
If it is the case that these variations are so uncertain, trivial, random and/or arbitrary, and thereby not useful indicators of climatic change; if they tell us little about the system being measured, then we are lead to turn the question around and ask: What do these graphs tell us about the science that constructs then, and all the other science that defers so much to their validity?
3. Early attempts to Chart Global Climate Variation
The early interest was in precipitation. In the late 19th century and early 20th century work the search for climatic trends left temperature trends as almost an after thought. The shift to an interest in temperature occurred towards the end of the warm 1930s when attention was drawn to a warming trend across the last 50 years.
1889 Eduard Brückner: Evidence of rhythmic climatic change across recent centuries
In the last two decades of the 19th century Brückner used various proxies in attempts to establish general changes in climate over recent centuries across the northern hemisphere and also across the globe. His most important work on the topic, Klimaschwankungen seit 1700 published in 1890, identifies an erratic rhythm of climatic change shifting between cold-wet and hot-dry more or less every 35 years. In the previous year he published a paper titled ‘In wie weit ist das heutige Klima konstant?’ ( translation here as Ch 3 ‘How constant is Today’s Climate?’). After his usual analysis of synchronised fluctuations in precipitation proxies he remarks ‘rain is not the only meteorological element displaying this kind of rhythmic variation‘ and thereby introduces two proxy temperature chart.
The first gives the anomaly derived from instrument temperature records in Europe and New England.
The second uses the timing of the graph harvest as a proxy of seasonal temperature and precipitation to chart back to the 1670s:
Here is a summary of Bruckner’s findings:
1914+ Ellsworth Huntington: Variations in precipitation across historical times
Huntington worked with the founder of dendrochronology, A E Douglass to produce a precipitation proxy record from the tree rings of the giant red wood stands in California. He adjusted his curve to Ernst Antevs’s estimated levels of Lake Owen in the Serra Nevada Range (Antevs with Gerard de Geer pioneered the analysis of varves.)
Huntington also compared these results with proxy results for precipitation in Central Asia. In this way he was trying to get a picture of changes, consistent and varied, across the northern hemisphere during historical times.
1926 C E P Brook: review and consolidation of historical climatology
Precipitation in Europe:
(In the 1949 edition this graph is replaced with a temperature graph.)
Precipitation/Climate in the USA
‘These curves cannot be regarded as measuring rainfall only; they must include other factors of tree growth such as temperature and sunshine.’ Brooks p382
1938 – 1961 Guy Callendar: Attribution of the global warming trend
See also the later graphs G.S. Callendar, “Temperature Fluctuations and Trends over the Earth.” Quarterly J. Royal Meteorological Society (1961) 87: 1-12.
1953 Gordon Manley: Central England Temperature Record
The original article of 1953 presented the data in a table. It was in the 1974 update that this graph appears. While this is the longest running instrument record, it is not from one station but is the adjusted and homogenized result of data from various stations. (The graph is from p42 of “Central England Temperatures : Monthly Means 1659 to 1973″, Quarterly Journal of the Royal Meteorological Society (1974), 100, pp389-403)
4. Global Mean Temperature Charts published after 1950
1950 H C Willett: Global Temperature trends of the past century
1961 Murray Mitchell Global: Global Temperature trends of the past century
1964-1966 H H Lamb: graphs used as the basis for the IPCC First Assessment sketch of average millennial temperature variation
In The Changing Climate (1966) Lamb published a Lecture of 1964 called ‘Britian’s Climate in the Past.’ It contains the below graph giving estimates of the variation in the temperatures of Central England that was repeated in later publications including 1988:
In M L Parry’s Climatic Change, Agriculture and Settlement 1978, appeared this graph:
In Climate History and the Modern World 1st Ed, 1982, p76, there is this similar graph:
Then in 1990 the IPCC First Assessment average global millennial temperature variation sketch:
The report cites Lamb rather vaguely but it seems evident that the sketch (c) variation over the last 1000 years is based on H H Lamb’s estimates for central England only.
1969 M I Budyko: Using data compiled under Sharova to compare northern hemisphere temperature anomaly with solar radiation
‘Fig 1 represents the secular variation of annual temperature in the northern hemisphere that was calculated from the maps of temperature anomalies for each month for the period 1881 to 1960 which were compiled at the Main Geophysical Observatory [USSR]….Line 2 gives the anomalies averaged by ten-year periods.’ The Russians collected their own data to produce a completely new looking graph which was frequently used in the USA including in an extended National Geographic article of November 1976.
This is updated by Vinnikov in 1980:
1981 – James Hansen: By including more data from the Southern Hemisphere hemispherical variation is demonstrated
This chart was updated in 1988 to show the new warming trend surpassing the mid-century peak:
1993-6 IPCC Second Assessment: Warmest Since 1400
While the IPCC Second Assessment does discuss evidence of Medieval warming and the possibility of a global, hemispheric or regional (European) precedent to recent generalised warming [see SAR Ch3 6.2], the problem of a supposed global or hemispheric Medieval Warm Period is mostly avoided with discussions of temperatures only after that period. Statements in SAR of ‘warmest’ ‘…in the last 6 centuries’ or ‘…since 1400′ fit with the speculation (at least since Deming’s 2006 testimonial) of a push around this time ‘to get rid of’ the Medieval Warm Period. However, convenient or otherwise, in the early 1990s there was simply a dearth of studies attempting even hemispheric reconstructions back that far. As we saw above, the ‘schematic’ millennial chart that appeared in the First Assessment was generalise global from Lamb’s regional chart without justification.
In 1993 Bradley and Jones published these charts:
The IPCC Second Assessment took the Northern Hemisphere chart from this paper, re-expressed the variations in degrees Celsius, and superimposed recent instrumental data:
1998 Michael Mann, Phil Jones and Keith Briffa: New Proxy Charts
First 23 April Mann et al in Nature giving Northern Hemisphere back to 1400:
Next in May 1998 Jones et al published charts for both hemispheres back 1000 years:
In a 4 June 1998 letter to Nature Briffa et al gives a northern hemisphere back to 1400:
In the summer of 1999 Barnett et al (pdf) compare the 3 charts in a ‘Status Report’ on the detection and attribution of recent climate change:
Barnett comments that “the disparity between these reconstructions at some times over the last 400 years is as large as the observed changes in global temperature over the last 100 years.’ [p2631]“
1999 Michael Mann: The Hockey Stick is Born
The Mann et al chart of 1998 is extended and published in October 1999 to give the Hockey Stick chart for the IPCC Third Assessment:
For current global mean temperature charts see the Climate4You Global Temperature page.
Readers: Any suggestion for additions welcome. Also, please kindly note any errors in the comments.