The 1970s Global Cooling Consensus was not a Myth

Introduction

This is a repost from my article in WUWT. Figures 1 and 2 have been added to the post because they were missed out in WUWT.

Purpose of Review

Whether or not there was a global cooling consensus in the 1970s is important in climate science because, if there were a cooling consensus (which subsequently proved to be wrong) then it would question the legitimacy of consensus in science. In particular, the validity of the 97% consensus on global warming alleged by Cook et al (2013) would be implausible. That is, if consensus climate scientists were wrong in the 1970s then they could be wrong now.

It is not the purpose of this review to question the rights or wrongs of the methodology of the 97% consensus. For-and-against arguments are presented in several peer-reviewed papers and non-peer-reviewed weblogs. The purpose of this review is to establish if there were a consensus in the 1970s and, if so, was this consensus cooling or warming?

In their 2008 paper, The Myth of the 1970s Global Cooling Scientific Consensus, Peterson, Connolley and Fleck (hereinafter PCF-08) state that, “There was no scientific consensus in the 1970s that the Earth was headed into an imminent ice age. Indeed, the possibility of anthropogenic warming dominated the peer-reviewed literature even then.” This conclusion intrigued me because, when I was growing up in the early 1970s, it was my perception that global cooling dominated the climate narrative. My interest was further piqued by allegations of “cover-up” and “skulduggery” in 2016 in NoTricksZone and Breitbart.

Therefore, I present a review that examines the accuracy of the PCF-08 claim that 1970s global cooling consensus was a myth. This review concentrates on the results from the data in the peer-reviewed climate science literature published in the 1970s, i.e., using similar sources to those used by PCF-08.

Review of PCF-08 Cooling Myth Paper

The case for the 1970s cooling consensus being a myth relies solely on PCF-08. They state that,”…the following pervasive myth arose: there was a consensus among climate scientists of the 1970s that either global cooling or a full-fledged ice age was imminent…A review of the climate science literature from 1965 to 1979 shows this myth to be false. The myth’s basis lies in a selective misreading of the texts both by some members of the media at the time and by some observers today. In fact, emphasis on greenhouse warming dominated the scientific literature even then.” [Emphasis added].

PCF-08 reached their conclusion by conducting a literature review of the electronic archives of the American Meteorological Society, Nature and the scholarly journal archive Journal Storage (JSTOR). The search period was from 1965 to 1979 and the search terms used were “global warming”, “global cooling” and a variety of “other less directly relevant” search terms. Additionally, PCF-08 evaluated references mentioned in the searched papers and references mentioned in various history-of-science documents.

In total, PCF-08 reviewed 71 papers and their survey found 7 coolingpapers, 20 neutral papers and 44 warming papers. Their results are shown in their Figure 1.

A cursory examination of Figure 1 indicates that there is a 62% warming consensus if we use all the data and this consensus increases to 86% pro-warming, if we were to ignore the neutral papers (as was done in the 97% consensus). Therefore, the Figure 1 data seems to prove the contention in PCF-08 that 1970s global cooling was a myth.

However, I find it difficult to believe that the 1970s media “selectively misread” the scientific consensus of the day and promoted a non-existent cooling scare. Therefore, I present an alternative to the PCF-08 analysis below.

Methodology of this Review

In this review, I use an identical methodology to PCF-08, i.e., I examine peer-reviewed scientific journals. Non-peer-reviewed newspaper and magazine articles are not used. A significantly larger number of papers are presented in the current review than were used in PCF-08.

The PCF-08 database of articles is used but this is extended to examine more literature. Note that examining all of the scientific literature would have been beyond my resources. However, my literature survey was facilitated by the work of Kenneth Richard in 2016 (hereinafter, KR-16) at NoTricksZone, in which he has assembled a large database of sceptical peer-reviewed literature.

Some people may wish to ignore the KR-16 database as being from a so-called “climate denier” blog. However, almost all of the papers in KR-16 are from peer-reviewed literature and consequently it is a valid database. It is also worth noting that 16 of the papers used in the KR-16 database are also contained in the PCF-08 database.

The combined PCF-08 and KR-16 databases form the benchmark database for the current review. It was intended to significantly extend the benchmark database but, on searching the relevant journals, only 2 additional papers were found and these were added to form the database for this review.

It should be noted that KR-16 states that there were over 285 cooling papers. However, many of these papers were deleted from the current review as not being relevant. For example, several papers were either outside the 1965-1979 reference period or they emphasise the minor role of CO2 but do not consider climate trends.

I agree with PCF-08 that no literature search can be 100% complete. I also agree that a literature search offers a reasonable test of the hypothesis that there was a scientific consensus in the 1970s. I reiterate that the resulting database used in this review is significantly larger than that used by PCF-08 and consequently it should offer a more accurate test of the scientific consensus in the 1970s.

Most of the papers in the review database acknowledge the global cooling from the 1940s to the 1970s (typically 0.3 °C global cooling). Therefore, deciding between cooling, neutral or warming was relatively straightforward in most cases; namely did the paper expect the climate regime during the 1940s-1960s period to either to continue from the date that the paper was published, or did it expect a different climate regime in the medium-to-long-term?

Notwithstanding the straightforward test described above, some of the papers make contradictory statements and are thus more difficult to classify. Consequently, their classification can include an element of subjectivity. Fortunately, there are very few papers in this category and consequently an inappropriate classification does not materially affect the overall results.

The test criteria are summarised in Table 1.

ClassificationTest of Classification of PapersTypical Examples from Papers
CoolingCooling expected to either continue or initiateKukla & Kukla (1972) “…the prognosis is for a long-lasting global cooling more severe than any experienced hitherto by civilized mankind.”
NeutralEither non-committal on future climate change or expects warming or cooling to be equally possibleSellers (1969) “The major conclusions that removing the arctic ice cap would have less effect on climate than previously suggested, that a decrease of the solar constant by 2-5% would be sufficient, to initiate another ice age, and that man’s increasing industrial activities may eventually lead to the elimination of the ice caps and to a climate about 14C warmer than today…”
WarmingWarming expected to either continue or initiateManabe & Weatherald (1967) “According to our estimate, a doubling of the CO, content in the atmosphere has the effect of raising the temperature of the atmosphere (whose relative humidity is fixed) by about 2C.”
Table 1: Summary of Classification System for Papers

The search terms “global cooling” and “global warming” used by PCF-08 are used in this review but they have been expanded to include “cool”, “warm”, “aerosol” and “ice-age” because these, more general terms, return a larger number of relevant papers. Additional search terms such as “deterioration”, “detrimental” and “severe” have also been included. These would fit into the PCF-08 category of “other less directly relevant” search terms. 

Several of the papers in the database are concerned about the effects of aerosol cooling and they state that this effect dominates the effect of the newly emerging CO2-warming science. Indeed, a few papers warn of CO2cooling.

However, PCF-08 do not include any papers that refer to aerosol cooling by a future fleet of supersonic aircraft (SST’s) but several papers in the 1970s assumed an SST fleet of 500 aircraft. This seems incongruous now but, to show that this number of aircraft is not unrealistic; Emirates Airlines currently have a fleet of 244 (non-supersonic) aircraft and 262 more on order. Therefore, I have included papers that refer to the effects of aerosols from supersonic aircraft and other human activities. Of course, supersonic travel was killed-off by the mid-1970s oil crisis.

Furthermore, a number of PCF-08 and KR-16 papers were re-classified (from cooling, neutral or warming) as summarised Table 2.

ReferenceOriginalAmended
Sellers (1969)WarmingNeutral
Benton (1970)WarmingNeutral
Rasool and Schneider (1972)NeutralCooling
Machta (1972)WarmingNeutral
FCSTICAS (1974)WarmingCooling
National Academy of Sciences (1975)NeutralCooling
Thompson, 1975WarmingNeutral
Shaw (1976)NeutralCooling
Bryson and Dittberner (1977)NeutralCooling
Barrett, 1978NeutralCooling
Ohring and Adler (1978)WarmingNeutral
Stuiver (1978)WarmingNeutral
Sagan et al. (1979)NeutralCooling
Choudhury and Kukla, 1979NeutralCooling
a. Amended Classifications to PCF-08 
ReferenceOriginalAmended
Budyko, 1969CoolingWarming
Benton (1970)CoolingNeutral
Mitchell, 1970CoolingNeutral
Mitchell (1971)CoolingWarming
Richmond, 1972CoolingNeutral
Denton and Karlén, 1973CoolingWarming
Schneider and Dickinson, 1974CoolingNeutral
Moran, 1974CoolingNeutral
Ellsaesser, 1975CoolingNeutral
Thompson, 1975CoolingNeutral
Gates, 1976CoolingNeutral
Zirin et al., 1976CoolingNeutral
Bach, 1976CoolingWarming
Norwine, 1977CoolingWarming
Paterson, 1977CoolingNeutral
Schneider, 1978CoolingWarming
b. Amended Classifications to KR-16 
Table 2: Amendments to Classification of Papers in Database

Two examples of the amendments to the classification of the papers in the database are explained below:

  1. The Benton (1970) paper is classified as “Cooling” in KR-16 but the paper states that, “In the period from 1880 to 1940, the mean temperature of the earth increased about 0.60C; from 1940 to 1970, it decreased by 0.3-0.4°C…The present rate of increase of 0.7 ppm per year [of CO2] would therefore (if extrapolated to 2000 A.D.) result in a warming of about 0.60C – a very substantial change…The drop in the earth’s temperature since 1940 has been paralleled by a substantial increase in natural volcanism. The effect of such volcanic activity is probably greater than the effect of manmade pollutants… it is essential that scientists understand thoroughly the dynamics of climate.” [Emphasis added]. Consequently, this paper is re-classified as neutral in this review. Not the “Cooling” classification in KR-16 and not the “Warming” the classification in PCF-08).
  2. The Sagan et al. (1979)  paper is classified as “Neutral” in PCF-08 but the paper states that, “Observations show that since 1940 the global mean temperature has declined by -0.2 K…Extrapolation of present rates of change of land use suggests a further decline of -1 K in the global temperature by the end of the next century, at least partially compensating for the increase in global temperature through the carbon dioxide greenhouse effect, anticipated from the continued burning of fossil fuels.” [Emphasis added]. Therefore, this paper is re-classified as cooling in this review (conforming to the KR-16 classification).

Results from Review & Discussion

The review database contains a total 190 relevant papers, which is 2.7 times the size of the PCF-08 database. Of the 190 papers in the review database, 162 full papers/books and 25 abstracts were reviewed (abstracts were used when the full papers were either pay-walled or could not be sourced). Furthermore, 4 warming papers from PCF-08 were not reviewed because they could not be sourced. Therefore, the PCF-08 classification was used for these papers in this review.

The results from the review are summarised in Figure 2.

It is evident from Figure 2 that, for the 1965-1979 reference period used by PCF-08, the number of cooling papers significantly outnumbers the number of warming papers. It is also apparent that there are two distinct sub-periods contained within the reference period, namely:

  1. The 1968-1976 period when the 65 cooling papers greatly outnumber the 22 warming papers (74% to 26%), if we ignore the neutral papers (as was done in the Cook et al (2013). The 74% to 26% majority is an overwhelming cooling consensus.  Additionally, this is probably the period when the 1970s “global cooling consensus” originated because cooling was clearly an established scientific consensus – not the myth that PCF-08 contend.
  2. The 1977-1979 period when warming papers slightly outnumber the cooling papers (52% to 48%) – a warming majority but not a consensus.

The following observations are also worth noting from Figure 2 for the 1965-1979 reference period:

  1. Of the 190 papers in the database, the respective number of papers are 86 cooling, 58 neutral and 46 warming. In percentage terms, this equates to 45% cooling papers, 31% neutral papers and 24% warming papers, if we use all of the data.
  2. The cooling consensus increases to 65% compared with 35% warming – a considerable cooling consensus, if we ignore the neutral papers (as was done in the Cook et al (2013).
  3. The total number of cooling papers is always greater than or equal to the number of warming papers throughout the entire reference period.

Although not presented in Figure 2, it is worth noting that 30 papers refer to the possibility of a New Ice-Age or the return to the “Little Ace-Age” (although they sometimes they used the term “Climate Catastrophic Cooling”). Timescales for the New Ice Age vary from a few decades, through a century or two, to several millennia. The 30 “New Ice Age” papers are not insignificant when compared with the 46 warming papers.

Conclusions

A review of the climate science literature of the 1965-1979 period is presented and it is shown that there was an overwhelming scientific consensus for climate cooling (typically, 65% for the whole period) but greatly outnumbering the warming papers by 3-to-1 during the 1968-1976 period, when there were 63 cooling papers (74%) compared with 22 warming (26%).

It is evident that the conclusion of the PCF-08 paper, The Myth of the 1970s Global Cooling Scientific Consensus, is incorrect. The current review shows the opposite conclusion to be more accurate. Namely, the 1970s global cooling consensus was not a myth – the overwhelming scientific consensus was for climate cooling.

It appears that the PCF-08 authors have committed the transgression of which they accuse others; namely, “selectively misreading the texts” of the climate science literature from 1965 to 1979. The PCF-08 authors appear to have done this by neglecting the large number of peer-reviewed papers that were pro-cooling.

I find it very surprising that PCF-08 only uncovered 7 cooling papers and did not uncover the 86 cooling papers in major scientific journals, such as, Journal of American Meteorological Society, Nature, Science, Quaternary Research and similar scientific papers that they reviewed. For example, PCF-08 only found 1 paper in Quaternary Research, namely the warming paper by Mitchell (1976), however, this review found 19 additional papers in that journal, comprising 15 cooling, 3 neutral and 1 warming.

I can only suggest that the authors of PCF-08 concentrated on finding warming papers instead of conducting the impartial “rigorous literature review” that they profess.

If the current climate science debate were more neutral, the PCF-08 paper would either be withdrawn or subjected to a detailed corrigendum to correct its obvious inaccuracies.

Afterword

I reiterate that no literature survey can be 100% complete. Therefore, if you uncover additional references then please send them to me in the comments. It would make this review much better if we could significantly increase the number of relevant references.

Additionally, if you disagree with the classification of some of the references then please let me know why you disagree and I will consider appropriate amendments. Your comments on classification would certainly increase the veracity of the review by providing an independent assessment of my classifications.

References

The references used in this review and their classification are included in the spreadsheet here:

References-Global Cooling Consensus.xlsx

Revision 02

29-Dec-2022: Minor errors corrected by Angus McFarlane.

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Is 1 °C Halfway to Hell?

Pro-anthropogenic Global Warming web sites are concerned that we are about to exceed the 1 °C value for the temperature anomaly (see Met Office, New Scientist and Skeptical Science) but is this really “uncharted territory” (Met Office) or halfway to New Scientist’s global warming hell of 2 °C?

It is shown in the following discussion that “1 °C: Halfway to Hell” is an ill-chosen headline – a more appropriate headline would be, “1 °C: Halfway to the Optimum”.

HadCRUT4 Data

The HadCRUT temperature anomalies are shown in Figure 1.

Figure 1-HadCRUT4 Overlay on 1850-1900 Ave-CompressedFigure 1: HadCRUT 1850-1900 Temperature Anomaly with 1961-1990 Overlay (After: Met Office Chart)

The Met Office chart in Figure 1 is unusual in that the HadCRUT anomaly data are usually referenced to the 1961-1990 mean temperature. Using a pre-industrial mean of 1850-1900 is not strictly correct because the industrial revolution began from approximately 1760 to sometime between 1820 and 1840 (Wikipedia). Consequently, the use of an 1850-1900 mean for pre-industrial temperatures is an arbitrary choice.

Therefore, I have overlain the HadCRUT4 data (1961-1990 mean), plotted as the blue line and it is evident from Figure 1 that using a mean of 1850-1900 raises the anomaly by ≈ 0.3 °C, when compared with the 1961-1990 mean. This gives the pre-industrial anomaly greater visual impact than the usual HadCRUT4 values.

The use of the 1850-1900 mean as the basis for the 1 °C rise is unusual because the IPCC reports have always refer to the 1961-1990 mean from HadCRUT for climate projections, e.g., see IPCC AR4 FAQ 3.1, Figure 1. However, we can use other data to determine a real pre-industrial mean as discussed below.

A Different Pre-industrial Benchmark

A chart from Ljungqvist (2010) is presented in Figure 2 that shows temperature fluctuations in the northern hemisphere for the last two millennia.

LjungqvistFigure 2: Reconstructed Extra-tropical (30-90 °N) Decadal Temperature Anomaly to 1961-1990 mean (after Ljungqvist, 2010)

The purpose of Ljungqvist (2010) is to assess the amplitude of the pre-industrial temperature variability. It is evident from Figure 2 that there have been previous warm and cold periods over the last two millennia but that most of the temperatures have been cooler than the 1961-1990 mean. Furthermore, Ljungqvist notes that the Roman Warm Period (RWP) and the Medieval Warm Period (MWP)

seem to have equalled or exceeded the AD 1961-1990 mean temperature level in the extra-tropical Northern Hemisphere.”

The following points are worth noting from Figure 2:

  1. The instrumental date (shown in red at the right hand side of the chart) represents a comparatively small portion of the data available.
  2. The modern proxy peak temperature is 0.082 °C, which is 0.114 °C lower than the MWP peak of 0.196 °C.
  3. Using 1850-1900 as the base for pre-industrial temperature is a relatively cold benchmark for temperature measurements. For example, the 1850-1920 instrumental mean is -0.299 °C, which is 0.495 °C lower the MWP peak.
  4. It is apparent that we could use the 1961-1990 as a suitable base for pre-industrial temperatures. We could even use the mean of the Medieval Warm Period, which is 0.041 °C higher than the 1961-1990 mean.

It is also worth noting that one of Ljungqvist’s conclusions is that,

“Since AD 1990, though, average temperatures in the extra-tropical Northern Hemisphere exceed those of any other warm decades the last two millennia, even the peak of the Medieval Warm Period, if we look at the instrumental temperature data spliced to the proxy reconstruction. However, Ljungqvist stresses that, “However, this sharp rise in temperature compared to the magnitude of warmth in previous warm periods should be cautiously interpreted since it is not visible in the proxy reconstruction itself [my emphasis]

Indeed, Ljungqvist states that the proxy records result in “flattening out” the values,

“that makes us unable to capture the true magnitude of the cold and warm periods in the reconstruction… What we then actually get is an average of the temperature over one or two centuries.”

In other words when comparing earlier temperatures we should be careful when comparing temperature readings – we should only compare proxies with proxies and not proxies with thermometers.

Same Data: Different Perception

There are good scientific reasons for displaying temperatures as anomalies because it allows widely different temperatures from geographically disparate regions to be compared. Nevertheless, they do not need to be displayed in the format of Figure 1. It appears that one of the intentions of displaying temperatures in the Figure 1 format is to depict the temperature rise as being unusual and rising rapidly. However, this is not the case.

A temperature change of approximately 1 °C for 165 years from 1850 to 2015 is almost undetectable by human beings. To illustrate this I use actual HadCRUT4 global temperatures (not anomalies) in Figure 3.

Global Ave Temperature 1850-1900Figure 3: Global Average Temperature (1850-2015)

The chart presented in Figure 3 uses the HadCRUT 1961-1990 mean (14 °C) global temperature as its baseline (see FAQ here) and the actual temperatures are derived by adding or subtracting the anomalies data here from the 14 °C baseline. Figure 3 is based on a diagram by Anthony Watts (published in Climate Change the Facts, 2014) and it gives a less alarming view of global warming when compared with the anomaly diagram in Figure 1.

The following points are worth noting from Figure 3:

  1. The current high value for temperature (September 2015) is 14.70 °C and the lowest recorded value of 13.45 °C occurred in 1911. The starting value of the HadCRUT4 series is 13.63 °C in 1850.
  2. I have used temperatures from my own personal experience to determine a reasonable scale for the vertical axis, ranging from a high of 51 °C in Dubai to a low of -16 °C in Scotland.
  3. I also show temperatures from my new home in Sydney. These are more benign than those in item (2) above but they still show a large range from a high of 45.8 °C to a low of 2.1 °C.

Furthermore, by using temperature data from environs in which I have lived, it is evident that a temperature change of 1 or 2 °C is very small and is not unusual for most flora, fauna and humans. Nevertheless, let us examine if a 2 °C rise would cause serious climatic damage by discussing the Holocene Optimum.

The Holocene Optimum

The first IPCC report FAR presented the diagrams shown if Figure 4 for temperature variations over the last ten thousand years, 4(b), and the last one thousand years, 4(c).

The charts in Figure 4 are based on the work of Lamb, who was the founding director of the Climatic Research Centre (CRU) that produces the HadCRUT temperature data in conjunction with the Met Office. HadCRUT data is used extensively by the IPCC.

Schematic of Glbal Temp Variation-Lamb-IPCC FARFigure 4: Schematic Diagrams of Global Temperature Variations (Source: FAR Figure 7.1)

The similarity between Figure 4(c) and Ljungqvist’s chart in Figure 2 is remarkable, considering that Figure 4 was published in 1990. The dotted line in diagrams 4(b) and 4(c) is stated in FAR as nominally representing conditions near to the beginning of the twentieth century. Unfortunately, the diagrams in Figure 4 do not show values for the temperature scale. Therefore, I use Marcott et al (2013), which is referenced in AR5 WG1, to supply these values.

Marcott et al (2013) has been criticised for showing a spurious uptick in temperature in the 20th century. Indeed, Marcott stated in the paper and in RealClimate that is uptick is “probably not robust.” Consequently, I have used Roger Pielke, Jr’s version of Marcott’s diagram as Figure 5, in which the spurious data are deleted.

Marcott Fig-1B Pielke-AmendmentFigure 5: Holocene Global Temperature Variations (Source: Marcott Figure 1B amended by Pielke)

Approximately 80% of the Marcott et al (2013) proxies are of marine origin and consequently underestimate the variability in land temperatures. Nevertheless, several useful conclusions are obtained by Marcott et al (2013), namely:

  1. “Global temperature for the decade 2000-2009 has not exceeded the warmest temperatures in the early Holocene.”
  2. “The early Holocene warm interval is followed by a long-term global cooling of ≈ 0.7 °C from 5,500 BP to 1850.”
  3. “The Northern Hemisphere (30-90°) experienced a temperature decrease of ≈ 2 °C from 7,000 BP to 1850.”

Spatial Distribution of Temperature during Holocene Climatic Optimum

Renssen et al (2012) use a computer simulation to derive early Holocene temperature anomalies. They call the Holocene Climatic Optimum the Holocene Thermal Maximum (HTM) and, in referring to their simulation, they state that,

“The simulated timing and magnitude of the HTM are generally consistent with global proxy evidence, with some notable exceptions in the Mediterranean region, SW North America and eastern Eurasia.”

The Renssen et al (2012) computer simulation is cited in AR5 WG1 and it presents the spatial distribution of peak temperature anomalies during the Holocene Climatic Optimum relative to a  1000-200 BP pre-industrial mean (see Figure 6).

Global characterization of the Holocene Thermal Maximum-Renssen et al-2012-Fig 3A.-compressedFigure 6: Global Variation of Holocene Thermal Maximum Anomalies (Source: Renssen et al, 2012)

It is evident from Figure 6 that most of Europe and North America experienced an anomaly of 2-3 °C during the Holocene Thermal Maximum (HTM) and Renssen et al (2012) offer the following conclusions:

  1. “At high latitudes in both hemispheres, the HTM anomaly reached 5 °C.”
  2. “Over mid-to-high latitude continents the HTM anomaly was between 1 and 4 °C.”
  3. “The weakest HTM signal was simulated over low-latitude oceans (less than 0.5 C) and low latitude continents (0.5-1.5 °C).”

I reiterate that Renssen et al (2012) use a pre-industrial mean of (1,000 to 200) BP, which is ≈ 0.3 °C less than the HadCRUT4 (1961-1990) mean. Therefore, we should add ≈ 0.3 °C to their values when comparing them with modern-day temperatures. Not withstanding the aforementioned, it should be noted that the Renssen et al values are peak values and that global temperatures would be lower than their peak values.

Discussion

Current temperatures are examined with regard to the approaching 1 °C anomaly and the following standpoints are evident from the discussion:

  1. Portraying current temperatures as an anomaly from the 1850-1900 mean gives the false impression that current temperatures are high because it is shown that temperatures during this period were very low when compared with other warm periods, either in the last two millennia (Ljungqvist, 2010) or in the early Holocene (Marcott et al, 2013 or Renssen et al, 2012).
  2. A reasonable mean for pre-industrial temperatures would be 1961-1900 because this mean compares well with actual mean temperatures that occurred during times that really were pre-industrial, e.g., the Roman Warm Period and the Medieval Warm Period.
  3. The change in temperature during the last 165 years is hardly visible in Figure 3 but such plots wouldn’t normally get people overly concerned. Conversely, when an anomaly plot is deployed, the vertical scale is highly magnified as shown in Figure 1. The magnified vertical scale gives a steep slope to the temperature rise in modern times, which conveys the impression that global warming is proceeding rapidly. To the contrary, and in reality, Figure 3 shows that temperatures have been very stable over the last century and a half.
  4. Less worrying anomaly plots than that shown in Figure 1 are presented in Figures 2 and 5. These show that current temperatures are not unusual when compared with earlier warm periods.
  5. Figure 6 (Renssen et al, 2012) shows that many parts of the world experienced temperatures during the early Holocene that were significantly greater than 2 °C above the pre-industrial

Conclusions

The following conclusions are evident from the above:

  1. Portraying current temperatures as an anomaly from an 1850-1900 pre-industrial mean gives the false impression that current temperatures are high because temperatures during 1850-1900 were amongst the lowest in the last 10,000 years.
  2. Global temperature for the decade 2000-2009 has not reached the warmest temperatures in the early Holocene.
  3. Northern Hemisphere temperatures would need to increase by at least 2 °C above the (1850-1900) pre-industrial mean to reach temperatures experienced during the Holocene Climatic Optimum.

I contend that “1 °C: Halfway to Hell” is an inappropriate headline – a more appropriate headline would be, “1 °C: Halfway to the Optimum”, especially, if you live in the Northern Hemisphere.

Climate Models 2011: Same Data – Different Conclusions

In his blog post 2011 Updates to model-data comparisons at Real Climate, Gavin Schmidt shows the diagram in Figure 1.

Figure 1: Real World Temperatures Compared with IPCC Model Ensemble (Schmidt, 2012)

Gavin states that, “Overall, given the latest set of data points, we can conclude (once again) that global warming continues.” My perception was that there had been some cooling over the last 15 years, therefore I have decided to check Gavin’s claims.

Gavin explains that the chart shows the annual mean anomalies from the IPCC AR4 models plotted against the surface temperature records from the HadCRUT3v, NCDC and GISTEMP products (it really doesn’t matter which). Everything has been baselined to 1980-1999 (as in the 2007 IPCC report) and the envelope in grey encloses 95% of the model runs.

At first glance the chart seems to show a good correspondence between real world temperature and the average of the IPCC models. However, the correspondence does not look quite so good when you compare the chart with the AR4 charts. I have updated AR4 Figures 1.1 and TS.26 to include the HadCRUT data up to May 2012 and discuss these as follows.

Figure 2 is derived from Figure 1.1 of IPCC AR4.

Figure 2: Global Average Temperature Compared with FAR, SAR & TAR (after AR4 Figure 1.1)

It should be noted in Figure 2 that I could not get the HadCRUT3 temperature to match exactly with the values in Figure 1.1 in AR4. Therefore, I had to adjust the HadCRUT3 data by adding 0.026 °C. I am not sure why I had to make the adjustment in the HadCRUT3 data, perhaps it is just a printing error in the AR4 diagram but this error also repeats elsewhere. It may be coincidence but the average temperature for 1961-1990 on which HadCRUT3 is based is 0.026 °C. Therefore, it may be that the AR4 chart is normalised to a zero temperature for the 1961-1990 period. However, I can find no information that confirms that this adjustment should be made.

Notwithstanding the above, it is evident from Figure 2 that the correlation between the adjusted HadCRUT3 data and the original AR4 Figure 1.1 data is very good. This applies to both the individual data points and the smoothed data. It is also evident that the temperature trend is significantly below the FAR estimate and is at the very low ends of the SAR and TAR estimates.

In order to compare Gavin’s diagram with actual global temperatures, I use Figure TS.26 from AR4 a shown in Figure 3.

Figure 3: Model Projections of Global Mean Warming Compared with Observed Warming (after AR4 Figure TS.26)

The following points should be noted regarding Figure 3 compared with AR4 Figure TS.26:

  1. I have deleted the FAR, SAR and TAR graphic from Figure TS.26 in Figure 3 because they make the diagram more difficult to understand and because they are already presented in Figure 2, in a form that is much easier to assimilate.
  2. The temperature data shown in AR4 Figure 1.1 does not correspond to that shown in Figure TS.26. The Figure 1.1 data appear to be approximately 0.02 °C higher than the corresponding data in Figure TS.26. I have assumed that this is a typographical error. Therefore, I have used the same 0.026 °C adjustment to the HadCRUT3 data in Figure 3 that was used for Figure 2.
  3. My adjusted HadCRUT3 data points are typically higher than those presented in Figure TS.26.
  4. Despite items (1), (2) and (3) above, there is very good agreement between the smoothed data in TS.26 and the adjusted HadCRUT3 data, particularly for the 1995-2005 period. It should be noted that AR4 uses a 13-point filter to smooth the data whereas HadCRUT uses a 21-point filter. Nevertheless, AR4 states that the 13-point filter gives similar results to the 21-point filter.

Comparing Gavin’s projections in the RC chart in Figure 1 with the official AR4 projections in Figure 3, the following points are evident:

  1. The emissions scenarios and their corresponding temperature outcomes are clearly shown in the AR4 chart. Scenarios A2, A1B and B1 are included in the AR4 chart – scenario A1B is the business-as-usual scenario. None of these scenarios are shown in the RC chart.
  2. Real world temperature (smoothed HadCRUT3) is tracking below the lower estimates for the Commitment emissions scenario., i.e., emissions-held-at-year-2000 level in the AR4 chart. There is no commitment scenario in the RC chart to allow this comparison.
  3. The smoothed curve is significantly below the estimates for the A2, A1B and B1 emissions scenarios. Furthermore, this curve is below the error bars for these scenarios, yet Gavin shows this data to be well within the error bands.
  4. The RC chart shows real world temperatures compared with predictions from models that are an “ensemble of opportunity”. Consequently, Gavin states, “Thus while they do span a large range of possible situations, the average of these simulations is not ‘truth’.” [My emphasis].

In summary, TS.26 from AR4 is useful for comparing real world temperature data with the relevant emissions scenarios. To the contrary, Gavin uses a chart which compares real world temperature data with average model data for which he states does not represent “truth.” I suggest that this is not much of a comparison and I conclude that the AR4 chart is a much more informative comparison.

I also conclude that it is evident from Figure 3 (AR4 Figure TS.26) that there has been a pause in global warming and that some cooling is occurring. It is certainly not as Gavin concluded that, “Overall, given the latest set of data points, we can conclude (once again) that global warming continues.” Whether or not this cooling pause is a longer-term phenomenon or temporary pause only time will tell.

2010 – The Hottest Year on Record: Is this a Cause for Concern?

GISS report that 2010 has tied with 2005 as being the hottest year on record. James Hansen, the director of GISS, said that, “If the warming trend continues, as is expected, if greenhouse gases continue to increase, the 2010 record will not stand for long.”

Is this a cause for concern?

GISS Data Compared with Hansen’s Scenarios (2006)

The GISS Land Ocean Temperature Index (LOTI) data up to January 2011 are shown in Figure 1. They are compared with the global warming models presented by Hansen (2006).


Figure 1: Scenarios A, B and C Compared with Measured GISS Land-Ocean Temperature Index (after Hansen, 2006)

The blue line in Figure 1 denotes the GISS LOTI data and Scenarios A, B and C describe various CO2 emission outcomes. Scenarios A and C are upper and lower bounds. Scenario A is “on the high side of reality” with an exponential increase in emissions. Scenario C has “a drastic curtailment of emissions”, with no increase in emissions after 2000. Scenario B is described as “most plausible” which is expected to be closest to reality. The original diagram can be found in Hansen (2006). It is interesting to note that, in his testimony to US Congress, Hansen (1988) describes Scenario A as “business as usual”, which somewhat contradicts his “on the high side of reality” statement in 2006.

It is evident from Figure 1 that the best fit for actual temperature measurements is currently the emissions-held-at-year-2000-level Scenario C. The current temperature anomaly is 0.61  °C. Therefore, even with temperatures at record highs, we are not experiencing the runaway temperatures predicted for the “business-as-usual” Scenario A. Indeed, for Scenario C with emissions curtailed at year-2000 levels, the rate of temperature increase is an insignificant 0.01 °C/decade.

It is also worth noting that we are currently at the lower end of the range of estimated temperatures for the Holocene optimum and the prior interglacial period. These occurred without human intervention or huge increases in carbon dioxide.

HadCRUT3 Compared with IPCC AR4

The above comparison based on Hansen (2006) uses relatively old climate models. Therefore, I have compared current HadCRUT3 temperature data with the latest IPPC AR4 (2007) models in Figure 2.

Figure 2: IPCC Scenarios A1B, A2 & B1 Compared with HadCRUT3 Temperature Data (after AR4, 2007)

Figure 2, which is based on IPCC AR4 Figure TS.26. I have added the HadCRUT3 data as blue dots. The black dots in the original TS.26 diagram appear to be HadCRUT3 data but are slightly misaligned. Therefore, I offset the HadCRUT3 data by adding 0.018°C to achieve a reasonable fit with the individual data points shown in AR4. The blue line with white dots the smoothed HadCRUT3 data. It is evident from Figure 2 that the smoothed curve gives an excellent fit with observed data presented as the solid black line in AR4. The current temperature anomaly is 0.52  °C.

The observed temperature trends in Figure 2 are significantly below the “likely” warming scenarios presented in AR4. Furthermore, as with the GISS data, the current HadCRUT3 trend is similar to the emissions-held-at-year-2000-level scenario.

Conclusions

Two comparisons are presented that compare GISS LOTI data and HadCRUT3 data with their respective temperature simulation models and the following conclusions are offered:

  1. Observed temperatures are significantly below the “most plausible” or “likely” high emissions scenarios. Instead, they are on a trajectory that is similar to the emissions-held-at-year-2000-level scenarios.
  2. Current temperatures are at the lower end of the range of estimated temperatures for the Holocene optimum and the prior interglacial period. These temperatures occurred without human intervention.

In summary, global temperatures may be reaching record highs but they are not following “runaway” trajectories suggested by computer models. Instead, they are following an insignificant warming trend of approximately 0.01 °C/decade.

Notwithstanding the above, it should be noted that time period for the comparison of actual temperature measurements with those predicted by computer models is still relatively short. Hansen (2006) suggests that we could expect reasonable results for distinction between the scenarios and useful comparison with the real world by 2015.

Response to #203 in Deltoid

Re #203

I see McFarlane still wants to waste his time and avoids looking up the measurements of cosmic rays for the past 40 years….I’ll point out one graph of cosmic ray flux here that shows no long term trend over the past 55 years. He still doesn’t seem to get it. Even if cosmic rays could influence climate (which is extremely unlikely anyway), they’re not going to change the climate because they’re not changing themselves. A few fringe scientists don’t change the rules of logic.

A Few Fringe Scientists?

A CERN press release here in 2006 describes the CLOUD experiment.

The goal of this experiment is to investigate the possible influence of galactic cosmic rays on Earth’s clouds and climate. It involves an interdisciplinary team comprising 18 institutes from 9 countries including USA and Russia.
This should answer Chris’s comment on “a few fringe scientists”.

Correlation between Recent Temperature Changes & Cosmic Rays
The cosmic ray fluctuation shown in Chris’s link is virtually identical to that shown in Fig 29 of the ISAC report here. I include a cut-down version of the ISAC diagram here for ease of reference.

It is evident that, by using data identical to that supplied by Chris, ISAC produce a very good correlation between temperatures and cosmic ray fluctuations. However, the ISAC conclusion is the opposite from that suggested by Chris.

Contrary to Chris’s claim that cosmic rays are not changing and therefore cannot cause a climate change; ISAC concludes that small changes in cosmic rays lead to large changes in the Earth’s climate.

Furthermore, ISAC cites many robust statistical correlations and a large number of pertinent references to validate their conclusion. Nevertheless, ISAC also highlights that the physical mechanisms of the solar-activity/cosmic-ray/climate correlation are poorly understood; hence the need for experimental verification, such as those being undertaken out at CLOUD and SKY.

Is this not the way that science works? Postulate a hypothesis. Test it by experiment. Prove it, improve it, or disprove it. Then move on.

Only time will tell if the cosmic-ray hypothesis is valid. It is currently at the test-it-by-experiment stage. Nonetheless, the research is being carried out by many respectable institutions and they are using valid scientific methodology. Consequently, it ill behoves Chris, or anyone else, to label this research as “fantasy land”

Hansen’s 1988 Climate Models: Response to Julien in Deltoid 2 August 2008

In Deltoid #203 on 29 July 2008 Julien Emile-Geay wrote:

It is simply astounding how climate skeptics have gotten cornered into such a tiny fraction of disinformation space that they must exhume 20-year old models to vainly poke holes into the current scientific literature.

Hence, McIntyre and his clique can’t get over Mann Bradley and Hughes (1998, 10 years old), and a lot of those who have no clue about GCMs think it’s fair game to throw dirt at Hansen’s GISS model predictions (1988). Meanwhile climate scientists have moved on : some results have survived, some have not, but the basic result remains – AGW is real, no amount of disingenuous PR will make it go away.

Given the simplicity and low resolution of Hansen’s 1998 model (which didn’t have anything remotely close to an ENSO, for instance), it is indeed remarkable that it was able to predict the temperature of the next 20 years to such accuracy. What the Skeptics keep missing (Mr McFarlane in particular) is that numerical modeling and computer power have done quite a bit of progress in the past 20 years, and no climate scientist is retarded enough to be hanging their hat over 1988 results.

Sure, there still are legitimate questions concerning the relative importance of natural vs anthropogenic climate variability, some of which have implications for policy initiatives, and that would deserve healthy debate. Yet the Skeptics are so blinded by their political prejudices that they keep fighting old windmills.

I can’t speak for every climate scientist, but the only reason why I’d ever show the Hansen 1988 figures at this day and age would be to demonstrate that the physics of greenhouse warming are rather basic (indeed, Arrhenius)
had figured it out over a century ago), and that a good radiative transfer code (which is what the GISS model is known for) is enough to produce credible global temperature trends given a realistic forcing.

Current GCMs are now focused on getting the regional scales right – that’s where the money is, and intelligent skeptics (I heard there were some) would be well inspired to get out of their rut and on board that train. If they keep whining at the 1988 stop we soon won’t be able to hear them.

So, now that we’ve got that one cleared, can we please talk about something more interesting ? Abrupt climate change, operational climate prediction, regional climate variability, link with tropical cyclones, to name a few…

Or is it that there just isn’t any stone left for the AGW skeptics to hide ?

My response on 2 August 2008 was:


Wow Julien! So many comments in such a brief response, but, unfortunately, liberally sprinkled with remarks such as disinformation, disingenuous, retarded, prejudices, etc. Nevertheless, I shall try to respond in a more rational manner.

Exhumation of 20-Year Old Models

It is simply astounding how climate skeptics have gotten cornered into such a tiny fraction of disinformation space that they must exhume 20-year old models to vainly poke holes into the current scientific literature.

If you read my posts above it is clear that I didn’t exhume Hansen’s 1988 model. Jim Hansen did. Furthermore, he published his models here in 2006 and stated here in 2006 that Scenario B “was dead on the money”. In addition, Tim Lambert said in #47 in this blog that:

Scenarios B and C don’t diverge until after 2006. Results so far are close to both B and C. In a few more years we’ll see if temperatures now stabilise (scenario C) or continue to increase (scenario B).

I agree with Tim, but my chart below shows that what looked to be a reasonable fit with Scenario B in 2006 does not look very good in 2008.

I reiterate my statement in #195, that:

It is early days yet, but it would appear that our planet is following the zero-emissions Scenario C.

From the foregoing, I contend that it is reasonable for me to comment on Hansen’s 2006 papers and posts in this blog without being accused of exhuming 20-year old models. Julien, perhaps you should target your responses at Jim Hansen. He was responsible for the initial exhumation of his 20-year old models.

Mann, Bradley & Hughes 1998 [MBH98]

I thought that McIntyre & McKitrick (M&M) did a well-balanced due-diligence on MBH98. Furthermore, despite more recent papers from the “Hockey Team” over the last 10 years, it would appear that M&M’s core conclusions still stand, namely: “no bristlecones, no hockey stick”.

Incidentally, the MBH98/M&M discourse was one of the reasons why I began to doubt the AGW hypothesis.

AGW is Real

AGW is real, no amount of disingenuous PR will make it go away.

Perhaps, but AGW is still currently a hypothesis. It has not yet been raised to a law of physics.

ENSO

Thank you for the Wikipedia link, but I didn’t need it. Nevertheless, I was half expecting a response stating that one of the reasons for the temperature drop in 2008 was that 2007-2008 was a La Nina.

Computer Power

A large part of my day job involves running complicated computer models and, therefore, I am well aware of the increased computational power available and the evolution of current GCMs. However, the GCMs that I am aware of “…don’t do clouds very well”, which may lead to incorrect temperature predictions.

Retarded Climate Scientists

… no climate scientist is retarded enough to be hanging their hat over 1988 results

I wouldn’t call Jim Hansen retarded for exhuming his 1998 model, but, if you so wish; it is your choice.

Arrhenius

I can’t speak for every climate scientist, but the only reason why I’d ever show the Hansen 1988 figures at this day and age would be to demonstrate that the physics of greenhouse warming are rather basic (indeed, Arrhenius)

I am well aware of Arrhenius’s work, but it would appear that this one should also be sent to Jim Hansen, because it refers to his exhumation of his 1988 models.

Other Topics

…can we please talk about something more interesting ? Abrupt climate change, operational climate prediction, regional climate variability, link with tropical cyclones, to name a few…

I agree. In 2007, my company employed Weather Intelligence, UK, to carry out research for us on regional climate variability and operational climate prediction.

Importance of Hansen’s Models

Chris O’Neill said on Deltiod

Gee, and I thought that twenty year old model was the be-all and end-all of climate forecasting.

My respnose was:

Chris, Hansen’s 20-yer old models presented in #109 are very important. They  are the  cornerstone of IPCC/your government policy. If they are wrong then your government is going the wrong way on CO2.

Yet in 2006 Hansen said here that Scenario B “was dead on the money”. It would now appear that he was wrong. Planet Earth appears to be tracking below the zero-emmissions Scenario C and Scenario B is not “dead on the money”; it is way too high.

GISS Temperature Data January-June 2008

Eli Rabbett re #192 on Deltioid wrote that

“This is the one with January standing for all of 2008”.

My response to Eli was that I stated that the temperature figures were for the first six months of the year. You can check the GISS surface station figures here or the land ocean data here.

I summarise the GISS Jan-Jun 2008 figures below for ease of reference:

GISS Temperature Data 

2008      Land       Land-
         Stations      Ocean

Jan               35             14
Feb               32             25
Mar               72             60
Apr               52             42
May              45             39
Jun               26             26
Average = 44           34

Note: 

  1. Surface Station Data Jan-Jun 2008 average = 0.44 °C.
  2. Land-Ocean Data Jan-Jun 2008 average = 0.34 °C.

The latest figures are well below my original Jan-May graph posted in Deltoid #190. It is evident from my graph, and the latest GISS figures, that the 2008 temperatures will be significantly below recent temperatures. They will probably be as low as 1995 or even, God forbid, 1990! It would appear that our planet is currently tracking below Hansen’s Zero-Emissions Scenario C. Good old planet Earth!

I reiterate, is it possible that a stabilisation of temperatures and/or global cooling, as predicted by the solar-cycle/cosmic-ray fraternity, is beginning to happen?

Eli, I look forward to your response.

Reliability of Hansen’s Climate Change Models

It would appear that Hansen’s 1988 climate models are beginning to diverge from the actual temperature observations

The latest GISS readings are shown in the diagram below:

Scenarios A, B and C Compared with Measured GISS Surface Station and Land-Ocean Temperature Data
Scenarios A, B and C Compared with Measured GISS Surface Station and Land-Ocean Temperature Data

The original diagram can be found in Fig 2 of Hansen (2006) and the latest temperature data can be obtained from GISS. The red line in the diagram denotes the Surface Station data and the black line the Land-Ocean data. My estimate for 2008 is based on the first six months of the year.

Scenarios A and C are upper and lower bounds. Scenario A is “on the high side of reality” with an exponential increase in emissions. Scenario C has “a drastic curtailment of emissions”, with no increase in emissions after 2000. Scenario B is described as “most plausible” and closest to reality.

Hansen (2006) states that the best temperature data for comparison with climate models is probably somewhere between the Surface Station data and the Land-Ocean data. A good agreement between Hansen’s premise and measured data is evident for the period from 1988 to circa 2005; especially if the 1998 El Nino is ignored and the hypothetical volcanic eruption in 1995, assumed in Scenarios B and C, were moved to 1991 when the actual Mount Pinatubo eruption occurred.

However, the post-2005 temperature trend is below the zero-emissions Scenario C and it is apparent that a drastic increase in global temperature would be required in 2009 and 2010 for there to be a return to the “Most-Plausible” Scenario B.

Will global warming resume in 2009-2010, as predicted by the CO2 forcing paradigm, or will there be a stabilsation of temperatures and/or global cooling, as predicted by the solar-cycle/cosmic-ray fraternity?

Watch this space!

P.S: It would be very interesting to run an “Actual Emissions” Scenario on the Hansen model to compare it with actual measurements. The only comments that I can glean from a literature survey is that Scenario B is closest to reality, but it would appear that CO2 measurements are above this scenario, but unexpectedly, methane emissions are significantly below. Does anyone have the source code and/or input data to enable this run?