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The CO2/Temperature correlation over the 20th Century

Posted on 18 June 2009 by John Cook

Previously, we looked at the correlation between CO2 and temperature over the past 40 years. However, as I'm always saying, you need to look at the broader view, not just a single piece of the puzzle. The 40 year period was chosen to demonstrate that even during a period of long term warming, internal variability causes periods of short term cooling. What if we look at a longer time series? Over the past century, are there any periods of long term cooling and if so, what is the significance?


Figure 1: CO2 green line derived from ice cores obtained at Law Dome, East Antarctica (CDIAC). CO2 blue line measured at Mauna Loa (NOAA). Global temperature anomaly (GISS)

Figure 1 compares CO2 to global temperatures over the past century. The first thing to clarify is that the relationship between CO2 and global temperature is not linear. As more CO2 is added, the warming effect has a diminishing return. Hence, the relationship between CO2 and temperature is logarithmic, not linear. A more appropriate comparison with CO2 is radiative forcing.

Radiative forcing is loosely described as the change in net energy flux at the top of the Earth's atmosphere. Eg - the change in how much energy the planet is accumulating or losing. The relationship between global temperature anomaly and radiative forcing is linear. Figure 2 compares greenhouse gas forcing (which is predominantly due to CO2 but includes smaller contributions from CH4, N2O and CFC) to global temperature anomaly.


Figure 1: Greenhouse gas forcing (GISS) and global temperature anomaly (GISS).

In truth, Figure 1 and Figure 2 both paint a similar picture. While CO2 is rising from 1940 to 1970, global temperatures show a cooling trend. This is a 30 year period, longer than can be explained by internal variability from ENSO and solar cycles. If CO2 causes warming, why isn't global temperature rising over this period?

The broader picture in this scenario is to recognise that CO2 is not the only factor that influences climate. There are a number of forcings which affect the net energy flux into our climate. Stratospheric aerosols (eg - from volcanic eruptions) reflect sunlight back into space, causing net cooling. When solar activity increases, the net energy flux increases. Figure 3 shows a composite of the various radiative forcings that affect climate.


Figure 2: Separate global climate forcings relative to their 1880 values (image courtesy NASA GISS).

When all the forcings are combined, the net forcing shows good correlation to global temperature. There is still internal variability superimposed on the temperature record due to short term cycles like ENSO. The main discrepancy is a decade centered around 1940. This is thought to be due to a warming bias introduced by US ships measuring engine intake temperature.


Figure 3: Net forcing (Blue - NASA GISS) versus global land ocean temperature anomaly (Red - GISS Temp).

So we see that climate isn't controlled by a single factor - there are a number of influences that can change the planet's radiative balance. However, for the last 35 years, the dominant forcing has been CO2.

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Comments 51 to 79 out of 79:

  1. "Denialists know the truth"

    Very true. But it is the AGW alarmists are the ones in denial. Wake up, it was predicted by Rhodes Fairbridge in the "Solar Jerk". Back in the summer of 2007 Mackey said it would be 2008-2011 to prove the hypothesis. Two years down, two correct predictions and three to go. That is two correct predictions for the "Denialists" and ZERO for the alarmists.
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  2. Nevertheless, the sun stays the same, the CO2 keeps rising, and so do the temperatures, as predicted. Now which denialist are you calling a "solar jerk"? I sympathise with the sentiment, but name-calling is not good. Oh, and I think the predictions from the alarmists (and only a fool, or a stooge, is not alarmed) are running somewhere about 25 to zip since Hansen first started ringing alarm bells.
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  3. Re: "Nevertheless, the sun stays the same, the CO2 keeps rising, and so do the temperatures, as predicted."

    Prove it. It is not warming, it's cooling. The air is cooling, the oceans are cooling. What planet do you live on?

    Re: Now which denialist are you calling a "solar jerk"?

    "The Solar Jerk" is not a person, it is the name of a hypothesis put toward in 1966 by Dr. Rhodes Fairbridge and the predictions by Dr. Mackey in summer 2007.

    "We are all toast" Hansen lost his mind several years ago.
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  4. "Prove it. It is not warming, it's cooling. The air is cooling, the oceans are cooling. What planet do you live on?"

    Is this sarcasm? While surface air T has never been a steady linear climb, it has been gaining on it's 1998 peak. And as to our oceans warming or cooling, everything I can find on ocean temperatures shows a continued climb. While I could understand some regional surface cooling (say, near increased glacial runoff areas, i.e. Greenland), could you post any links showing oceans in general are actually cooling?
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  5. Thumb
    It's up to you to prove that it is warming. So far we see broken satellites, broken weather sensors, excuses for why the machines do not show reality unless they fudge the data.

    Show the proof that it is warming? Even the IPCC said it's cooling. NASA said it's cooling. Where do you get your data from?
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  6. "I'm sure the majority (but not all) of my IPCC colleagues cringe when I say this, but I see neither the developing catastrophe nor the smoking gun proving that human activity is to blame for most of the warming we see. Rather, I see a reliance on climate models (useful but never "proof") and the coincidence that changes in carbon dioxide and global temperatures have loose similarity over time."
    FROM: My Nobel Moment - By JOHN R. CHRISTY

    I could list all the articles from scientists but John asks us not to make lists of links. I think this one is a good example of good scientists that are more than skeptic about the whole fiasco.
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  7. "It's up to you to prove that it is warming"

    Have you been watching the Arctic or Greenland? What about glacier retreat in general, or the rising ocean levels? I thought the new argument was that the Earth was warming but it's not our fault. Now the argument is, in spite of the events I listed above, that the earth is cooling because it's not warming in a straight linear progression since it's peak in 1998? Or is it that it's warming but it's all a big multi-decades long lag effect from the sun?

    It's really tough to keep up sometimes.
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  8. Question. So I know from the Calvin cycle and from the relative pH of water that as temperatures warm up they CAUSE carbon dioxide levels to increase. Isn't it a circular argument to say that inverse. Wouldn't the temperatures just simply continue to increase if both statements are true?
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  9. Question. So I know from the Calvin cycle and from the relative pH of water that as temperatures warm up they CAUSE carbon dioxide levels to increase. Isn't it a circular argument to say that inverse. Wouldn't the temperatures just simply continue to increase if both statements are true?
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  10. re50:
    "that no environmental concern must ever get in the way of, hell, must never even pause, neoconservative laissez faire unregulated capitalism for the very rich - and therefore no fact can ever demonstrate the failure of their ideology"...

    Yawn. I suppose radical socialist-intellectuals have a completely rosy record?? Did it ever occur to you that bureaucrats and intellectuals can have self-serving interests/bias? Who regulates the regulators?? (Note: Karl Marx scoffed at the idea that the new 'factory managers' could be tempted to distort/exploit the system for their own benefits. What naivety).

    The question is not left versus right, or market forces versus socialist ideology and/or regulation, but a breakdown in regulation/uncertainties in modelling/ideology in human thought (ie on both 'sides').

    If you want historical examples of where intellectualism and modelling/ideology can go drastically wrong (on both 'sides'):

    - Richard Pipes of Harvard blames radical academics for providing the foundation, framework and justfication for radical Bolshevic communism in the late 19th century-early 20th century.
    -Weikart blames German Social Darwinists and intellectuals in the late 19th-early 20th century for providing the foundation, framework and justification for radical Nazism
    -Social Darwinists/Eugenics movement came from within radical academics and intellectuals, who also attempted to impose their 'science model' on the world in the early 20th century (with Nazism as an offshoot of this).
    -The financial crisis of 2000s, where the 'expert banks' and their modellers got it all wrong.
    -Human-induced global warming modellers, (>90% sure that there is >90% effect from human activity).

    The jury is still out on the last one, but their general manner and methods, in my opinion, are not all that dissimilar to the previous ones. AGW just could be a form of socialist-determinism-the bane of the 20th century-eg in biology and ethics (eugenics), radical socialism (communism), Nazism (biology and race), AGW (?socialist-determinist distortion and control of energy?)
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  11. Usoskin correlated cosmogenic isotopes of beryllium and carbon with a global temperature reconstruction and found the best fit with a 10 year lag. The isotopes are formed when hit by cosmic radiation which is modulated by heliospheric magnetic intensity. The likely connection of cosmic rays to climate is in ionisation of aerosols in the atmosphere and subsequent growth of cloud condensation nuclei.

    Heliospheric magnetic intensity peaked late last century on at least a thousand year high – in fact, as Usoskin shows, a very similar hockey stick shape as temperature. With the appropriate bends for the medieval warm period and the little ice age.

    Usoskin’s data stopped in 1975 – but the comment was made that global temperature and heliospheric modulation of cosmic rays diverged after 1975 and this has been repeated ad nauseum. Usoskin makes a more measured contribution to this latter discussion here:

    Usoskin et al - Heliospheric modulation of cosmic rays:
    Monthly reconstruction for 1951–2004

    http://cosmicrays.oulu.fi/phi/2005JA011250.pdf

    The cosmic ray modulation parameter is shown to peak around 1991 and this is entirely consistent with global temperature and cloud parameters.

    The idea that sulphur dioxide masked warming between the mid 1940’s and 1975 isn’t realistic as the GISS calculated net forcing is positive other than in episodic (and short lived) periods of volcanic perturbation. The cooling is especially evident in the Artic temperature record.

    The Pacific Decadal Oscillation is a clue to the underlying cause of mid century cooling. The cool period of the PDO extended from the 1946 to 1975 but could a tiny cool spot in the north eastern Pacific affect global temperature so dramatically? Hardly likely. The PDO is associated with changes in ENSO. Cool modes bring more intense and frequent La Niña and warm modes more frequent and intense El Niño. We can show this with statistical analysis of rainfall records – which was my starting point. However, I doubt that even that is much of a multi decadal cooling influence.

    Instead, I believe the 20 to 30 year PDO is an effect rather than a cause. The heliospheric link to clouds appears to be firmly based in science and the heliosphere varies on a 22 year solar magnetic polar reversal cycle. The polar magnetic reversal occurs in the 11 year solar cycle about 2 years after solar maximum. There is an 11 year period of higher magnetic intensity followed by 11 years of reduced magnetic intensity. This is obviously a thought in progress – I think I need another 20 years of data.

    Nonetheless, I am working on the assumption that there is actual shortwave heating and cooling of the world ocean on 20 to 30 years cycles. There is a balance between the resistance of a warm surface layer to the penetration of cold subsurface currents and this is particularly apparent in the sweet spot in the north eastern Pacific. A little cooling and cold water upwells strongly. A little warming and it is suppressed. The same heating and cooling happens in the central Pacific with a 2 to 7 year ENSO cycle superimposed.

    The shortwave heating and cooling shows up in International Satellite Cloud Climatology Project records. Declining cloud cover from the start of records in 1984 to 1998 and about 4W/m2 additional shortwave radiation at the surface. Increasing cloud cover from 1999 to 2008 and about 2 W/m2 less shortwave radiation.

    The PDO was originally defined in terms of fisheries productivity associated with sea surface temperature changes. Upwelling cold and nutrient rich water in a cool mode provides a huge boost to fisheries and the reverse happens in a warm mode. The biological indicators suggest that the current cool mode commenced after 1999.

    There’s at least three linked sceptical arguments and one that is totally original – heard here first. Surely, I get sceptic of the week?

    Cheers
    Robbo
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  12. re 61: pretty good post.

    I think clouds are the key, they will enhance solar increases signficantly.

    Also your point:
    "The idea that sulphur dioxide masked warming between the mid 1940’s and 1975 isn’t realistic as the GISS calculated net forcing is positive other than in episodic (and short lived) periods of volcanic perturbation"

    Another problem with the aerosol idea ~1950-1980 is that they contradict what actually happened in the USA/Europe where they were being emitted between 1950-1980-these were the same areas where surface T increased mostly in the 20th Century...
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  13. Thumb
    The Arctic is not about CO2. It's about tectonic plates. We did not about the increase in the Arctic ridge until the past couple of years, It was even not about the under volcanoes erupted until they put together the quakes with the eruptions BEFORE the recent eruptions in Alaska. They also show the subduction zone in NE Greenland but they recognize the thin crust and hot spot and Greenland active volcanoes the "might add to the glacier melt". See the volcano threat here.
    http://www.skepticalscience.com/volcanoes-and-global-warming.htm
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  14. "We did not about the increase"
    s/b We did not KNOW about the increase
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  15. "The Arctic is not about CO2. It's about tectonic plates." - what an astonishing coincidence then, that the unprecedented melt is happening just as temperatures rise with increasing CO2.
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  16. When reading the amazing theses from Thingadonta, Robbo, and Quietman, I am constantly reminded of something you learn very early on when training to be a scientist - a certain aphorism by Mr Ockham.
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  17. Seriously - did no one that the post confused sea surface temperatures and than near surface atmospheric temperature. There is a link by energy transfer but the series are measured in different ways.

    The temperature is measured in water - air temperature is measured in air. The fact that they both show cooling trends?

    Oceans surfaces cooled after the mid 1940's as did near surface atmosphere temperature. The warming and cooling was especially pronounced in the Arctic.

    Arctic air temperature change amplification and the Atlantic Multidecadal Oscillation
    Chylek Petr, Chris K. Folland, Glen Lesins, Manvendra K. Dubeys, and Muyin Wang: 2009: 'Arctic air temperature change amplification and the Atlantic Multidecadal Oscillation'. Geophysical Research Letters (in press).

    “Understanding Arctic temperature variability is essential for assessing possible future melting of the Greenland ice sheet, Arctic sea ice and Arctic permafrost. Temperature trend reversals in 1940 and 1970 separate two Arctic warming periods (1910-1940 and 1970-2008) by a significant 1940-1970 cooling period. Analyzing temperature records of the Arctic meteorological stations we find that (a) the Arctic amplification (ratio of the Arctic to global temperature trends) is not a constant but varies in time on a multi-decadal time scale, (b) the Arctic warming from 1910-1940 proceeded at a significantly faster rate than the current 1970-2008 warming, and (c) the Arctic temperature changes are highly correlated with the Atlantic Multi-decadal Oscillation (AMO) suggesting the Atlantic Ocean thermohaline circulation is linked to the Arctic temperature variability on a multi decadal time scale.”

    “In the following analysis we confirm that the Arctic has indeed warmed during the 1970-2008 period by a factor of two to three faster than the global mean in agreement with model predictions but the reasons may not be entirely anthropogenic. We find that the ratio of the Arctic to global temperature change was much larger during the years 1910-1970.” “We consequently propose that the AMO is a major factor affecting inter-decadal variations of Arctic temperature and explaining [the] high value of the Arctic to global temperature trend ratio during the cooling period of 1940-1970.”

    Again, ocean and atmospheric temperatures are heading down in this 25 year cycle. Which bit of multi-decadal oscillation is so hard to grasp?
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  18. I suppose it is simple to not see the wods for the trees. The post did confuse sea surface temperatures and with near surface atmospheric temperature. There is a link by energy transfer but the series are measured in different ways.

    Water temperature is measured in water - air temperature is measured in air. They are a different data series and provide independant support for the mid century cooling.
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  19. Seriously - did no one that the post confused sea surface temperatures and than near surface atmospheric temperature. There is a link by energy transfer but the series are measured in different ways.

    The temperature is measured in water - air temperature is measured in air. The fact that they both show cooling trends?

    Oceans surfaces cooled after the mid 1940's as did near surface atmosphere temperature. The warming and cooling was especially pronounced in the Arctic.

    Arctic air temperature change amplification and the Atlantic Multidecadal Oscillation
    Chylek Petr, Chris K. Folland, Glen Lesins, Manvendra K. Dubeys, and Muyin Wang: 2009: 'Arctic air temperature change amplification and the Atlantic Multidecadal Oscillation'. Geophysical Research Letters (in press).

    “Understanding Arctic temperature variability is essential for assessing possible future melting of the Greenland ice sheet, Arctic sea ice and Arctic permafrost. Temperature trend reversals in 1940 and 1970 separate two Arctic warming periods (1910-1940 and 1970-2008) by a significant 1940-1970 cooling period. Analyzing temperature records of the Arctic meteorological stations we find that (a) the Arctic amplification (ratio of the Arctic to global temperature trends) is not a constant but varies in time on a multi-decadal time scale, (b) the Arctic warming from 1910-1940 proceeded at a significantly faster rate than the current 1970-2008 warming, and (c) the Arctic temperature changes are highly correlated with the Atlantic Multi-decadal Oscillation (AMO) suggesting the Atlantic Ocean thermohaline circulation is linked to the Arctic temperature variability on a multi decadal time scale.”

    “In the following analysis we confirm that the Arctic has indeed warmed during the 1970-2008 period by a factor of two to three faster than the global mean in agreement with model predictions but the reasons may not be entirely anthropogenic. We find that the ratio of the Arctic to global temperature change was much larger during the years 1910-1970.” “We consequently propose that the AMO is a major factor affecting inter-decadal variations of Arctic temperature and explaining [the] high value of the Arctic to global temperature trend ratio during the cooling period of 1940-1970.”

    Again, ocean and atmospheric temperatures are heading down in this 25 year cycle. Which bit of multi-decadal oscillation is so hard to grasp?
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  20. 66#....In the scientific method, Occam's razor, or parsimony, is an epistemological, metaphysical, or heuristic preference, not an irrefutable principle of logic, and certainly not a scientific result. As a logical principle, Occam's razor would demand that scientists accept the simplest possible theoretical explanation for existing data. However, science has shown repeatedly that future data often supports more complex theories than existing data. Science tends to prefer the simplest explanation that is consistent with the data available at a given time, but history shows that these simplest explanations often yield to complexities as new data become available.

    (Wikipedia)

    Should we just dust our hands and say since AGW is the simplest hypothesis let's look no further? Don't let's explore other possibilities..even if they turn out to be dead ends? Surely scientific method includes probing and proving both negatives and positives?
    Has our research into climate produced nothing at all that detracts from the simple CO2 model?
    Are we that confident GCM's include all that is necessary to project both forward and backward with a high degree of accuracy? If so, why do they fail to do so?
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  21. re #70

    Not really Mizimi. Occams razor doesn't say anything about the acceptance of the simplest possible explanation.

    A better phrasing of Occam's razor is: "don't multiply causes unnecessarily".

    When applied to scientific enquiry we're still left with the question of evidence, and this is the gold standard within which Occam's razor is a useful adjunct. So we don't reject cosmic ray flux or vague tectonic contributions to the major late 20th century and contemporary warming merely because these are unnecessary multiplications of causes. We reject them because they don't have a basis in evidence, and the abundant evidence that exists doesn't support these as significant causal explanations.

    Of course that doeesn't mean that the cosmic ray flux and tectonic events shouldn't be studied. Far from it, and many scientists study the CRF and tectonic processes. The scientific literature has abundant publications on these interesting subjects. However scientists don't pretend that these have significant evidence towards causality in relation to contemporary global warming, and therefore don't attempt to "multiply causes unnecesarily". That's the role of the unscrupulous and misguided (and their dodgy websites!).

    Once one understand the handy use of Occam's razor within the scientific philosophy of empirical evidence interpreted within sound theoretical understanding, we can stop playing semantic games and ignore tedious and trite leading questions....
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  22. Senator Steve Fielding has posted his 3 questions to Climate Change Minister Penny Wong, her answers and his assessment.

    http://www.stevefielding.com.au/climate_change/

    Any comments with regards to the science and arguments of Senator Fielding and the Carter/Evans/Franks/Kinimonth's Due Diligence assessment?

    Thanks.
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  23. re #72: There's a thorough demolition of the "Due Diligence" (hah!) report at tamino's blog (see http://tamino.wordpress.com/2009/06/26/embarrassing-questions/ )
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  24. re #73

    Thanks Alliecat. I'll check out the link. Cheers!
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  25. John,

    This paper might be of interest: http://www.cccma.ec.gc.ca/papers/ngillett/PDFS/nature08047.pdf

    It also illustrates that although the empirical relationship between CO2 and temp is logarithmic, on shorter timescales and due to other climatic factors, it can be represented linearly. See also: http://moregrumbinescience.blogspot.com/2009/03/does-co2-correlate-with-temperature.html

    Great work!
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  26. "However, for the last 35 years, the dominant forcing has been CO2."
    Really?
    This figure http://doskonaleszare.blox.pl/resource/emisje2.png, in the polish alarmist blog, shows an increase of CO2 (by atmosphere exactly) in the years in ppm per year (rocznie = year) - the red curve; and anthropogenic emissions - a black curve (source: CDIAC).
    Compare the red curve, for example, the figure: http://www2.sunysuffolk.edu/mandias/global_warming/images/10_years_no_cooling.jpg.
    Interesting, is not it?
    CO2 decide about the temperature... whether is rather the opposite?

    Solar activity by Oceanic Warm Index - ocean heat capacity - 35 - "40 year lag periods"; by temperature... - the discussion shows that it is possible.
    "the negative aerosolic forcing has increased since the 1950’s"
    In central Asia "negative aerosolic forcing" increased since the 1950’s, even though the temperature are also increased...
    "TSI variation are very small." - Temperature also. 0,74 - UHI (rather not city but country - f.e. Japan; or continental UHI - Europe) or NBL, etc..., ... and temperature increasing becomes very small.

    Solar energy is redistributed in a number of cycles of even 1500-year..., after the completion of this remember about thermocline...
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  27. "However, for the last 35 years, the dominant forcing has been CO2."
    Really?
    This figure http://doskonaleszare.blox.pl/resource/emisje2.png, in the polish alarmist blog, shows an increase of CO2 (by atmosphere exactly) in the years in ppm per year (rocznie = year) - the red curve; and anthropogenic emissions - a black curve (source: CDIAC).
    Compare the red curve, for example, the figure: http://www2.sunysuffolk.edu/mandias/global_warming/images/10_years_no_cooling.jpg.
    Interesting, is not it?
    CO2 decide about the temperature... whether is rather the opposite?

    Solar activity by Oceanic Warm Index - ocean heat capacity - 35 - "40 year lag periods"; by temperature... - the discussion shows that it is possible.
    "the negative aerosolic forcing has increased since the 1950’s"
    In central Asia "negative aerosolic forcing" increased since the 1950’s, even though the temperature are also increased...
    "TSI variation are very small." - Temperature also. 0,74 - UHI (rather not city but country - f.e. Japan; or continental UHI - Europe) or NBL, etc..., ... and temperature increasing becomes very small.

    Solar energy is redistributed in a number of cycles of even 1500-year..., after the completion of this remember about thermocline...
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  28. I recommend this figure also in English http://www.jennifermarohasy.com/blog/archives/Jan%20Pompe_co2%20and%20temp2.gif
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  29. Arkadiusz Semczyszak,

    Whether it is the opposite?

    It can be the opposite and it can be the way it is now. CO2 can act as a feedback and a forcing. This is pretty straightforward science.
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