Arguments
Does CO2 always correlate with temperature (and if not, why not?)
What the science says...
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Surface temperature measurements are affected by short-term climate variability, and recent warming of deep oceans |
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Climate Myth...
There's no correlation between CO2 and temperature
"Twentieth century global warming did not start until 1910. By that time CO2 emissions had already risen from the expanded use of coal that had powered the industrial revolution, and emissions only increased slowly from 3.5gigatonnes in 1910 to under 4gigatonnes by the end of the Second World War.
It was the post war industrialization that caused the rapid rise in global CO2 emissions, but by 1945 when this began, the Earth was already in a cooling phase that started around 1942 and continued until 1975. With 32 years of rapidly increasing global temperatures and only a minor increase in global CO2 emissions, followed by 33 years of slowly cooling global temperatures with rapid increases in global CO2 emissions, it was deceitful for the IPCC to make any claim that CO2 emissions were primarily responsible for observed 20th century global warming." (Norm Kalmanovitch).
At a glance
If you happen to be reading something about climate change in the popular media, be sure to keep an eye out for certain words. The one in this case is 'deceitful'. Why? Because it's an emotive word. It's a good sign that the writer is not a scientist but someone with a political axe to grind.
The heat-trapping properties of carbon dioxide, water vapour and other greenhouse gases were identified over 160 years ago. After that, climate research continued unhindered for many decades. However, by the second half of the 20th century the seriousness of the threat of climate change was well-understood. That led in due course to the involvement of bodies such as the United Nations. Treaties such as the Kyoto Protocol of 1997 followed.
In response, the fossil fuels sector and their political and media associates, perceiving threats to profitability, turned climate science into a political football. With climate science thus politicised, the arena within which research and outreach were conducted had changed. This was no longer a quiet backwater.
That's the historical context. Now we can get to the meat of the myth. The quote above this piece dates from September 2009. Apart from anything else, it's 14 years out of date now. Globally, the ten warmest years since 1880 have all occurred since the statement was made. According to NASA’s Goddard Institute for Space Studies, the average global temperature has increased by 1.4° Celsius (2.5° Fahrenheit) since 1880.
However, global temperature does not correlate exactly with CO2 emissions on a year in, year out basis.There are other well-understood factors that can warm or cool the climate over such short-term periods. You may have heard of El Nino and La Nina. These phenomena involve above- or below-average sea surface temperatures respectively, in the central and eastern Pacific Ocean. Their effects are global.
A strong El Nino can produce a massive global temperature-spike. Such very warm years once led to people making the claim of, "no warming since 1998". Briefly sounding plausible for a few years, it soon became self-evidently incorrect.
Instead, the correct way to look at temperature trends is to examine them over multiple decades - 30 years is standard in climate science. So to answer the question, "where are we now?", one would look at the temperature record from 1992-2022. Doing so takes out the noise, the ups and downs due to El Nino, La Nina and other factors. And the trend is most certainly upwards.
To the newcomer to climate science, it can be difficult to spot misinformation. However, opinion-pieces that accuse bodies such as the Intergovernmental Panel on Climate Change (IPCC) of intentions like deceit should instantly ring alarm-bells.
It is important to point out that the motive for such political misinformation is to spread confusion and doubt. The organisations behind it simply seek delaying any meaningful action. In kicking the can down the road, they try to deflect the pressure to get their own houses in order, and to hell with the consequences.
Please use this form to provide feedback about this new "At a glance" section. Read a more technical version below or dig deeper via the tabs above!
Further details
The amount of CO2 in our atmosphere is increasing all the time. On February 26th 2024, according to the monitoring resource Daily CO2, it had exceeded 425 parts per million (ppm). That's up by 3.96 ppm since the same time last year - but more importantly, up from around 280 ppm before the industrial revolution - a 50% plus increase.
Pre-industrial levels of CO2 and other greenhouse gases, like methane and water vapour, were sufficient to keep the Earth’s surface 30°Celsius (54°F) warmer than it would have been without them. Since then, we have added 50% more CO2 - but that doesn't mean the temperature will go up by 50% too.
There are several reasons why. Doubling the amount of CO2 does not double the greenhouse effect. The way the climate reacts is also complex and it can be difficult to separate the effects of natural changes from man-made ones over short periods of time.
As the amount of man-made CO2 goes up, temperatures rise but not at the same rate. Estimates vary - climate sensitivity is a hot topic in climate science, if you’ll forgive the pun. Based on multiple lines of evidence, according to the IPCC Sixth Assessment Report (2021), the "very likely range [for climate sensitivity to doubling of CO2] is 2°C to 5°C".
So far, the average global temperature has gone up by about 1.4 degrees C (2.5 F).
"In 2023, hundreds of millions of people around the world experienced extreme heat, and each month from June through December set a global record for the respective month. July was the hottest month ever recorded. Overall, Earth was about 2.5 degrees Fahrenheit (or about 1.4 degrees Celsius) warmer in 2023 than the late 19th-century average, when modern record-keeping began."
Source: NASA.
The speed of the increase is worth noting too. Unfortunately, as this quote from NASA demonstrates, anthropogenic climate change is happening very quickly compared to changes that occurred in the past (text in bold for emphasis):
"As the Earth moved out of ice ages over the past million years, the global temperature rose a total of 4 to 7 degrees Celsius over about 5,000 years. In the past century alone, the temperature has climbed 0.7 degrees Celsius, roughly ten times faster than the average rate of ice-age-recovery warming."
Source: NASA Earth Observatory.
Small increases in temperature can be hard to measure over short periods, because they can be masked by natural variation. For example, cycles of warming and cooling in the oceans such as the El Niño-Southern Oscillation (ENSO) cause temperature changes that can mask small changes in temperature caused by CO2 emissions that occur at the same time. That's why scientists measure changes over long periods so that the effects of short natural variations can be distinguished from the effects of man-made CO2.
The rate of surface warming varies year by year, yet the physical properties of CO2 and other greenhouse gases do not change. Neither has the amount of energy arriving from the sun changed significantly in recent decades. But if that’s true, where is this heat going?
The answer is into the oceans. Fig. 1 is a graphic showing where the heat is currently going:
Figure 1: Global Energy Inventory: observed changes in the global energy inventory for 1971–2018 (shaded time series) with component contributions as indicated in the figure legend. Cross-Chapter Box 9.1 Figure 1 (part a) - From IPCC AR6 WGI Chapter 9.
The way heat moves in the deep oceans was poorly understood up until around the turn of the millennium. Since then, vast improvements in measurement techniques, such as the Argo float system, have allowed scientists to far more accurately gauge the amount of energy the oceans are absorbing. Argo floats, numbering several thousands, weigh 20-30 kilograms and are packed with instruments. They typically travel through the oceans around a kilometre below the surface. But they can rise up to the surface or dive down to 2 km. That makes it possible to collect profiles in terms of temperature, salinity and other parameters. So far, over two million such data-profiles have been collected.
Argo data have shown the upper 2,000 metres of the oceans has captured roughly 90% of the anthropogenic change in ocean heat content since the programme started in 1999. Temperatures in the upper 600 metres have been seen to fluctuate with shorter-term climate events like El Niño-Southern Oscillation. In deeper waters, however, there is a more consistent warming trend. In summary, the 700–2,000 metres ocean layer accounts for approximately one-third of the warming of the whole 0–2000 m layer of the World Ocean being mapped by the Argo floats.
So we know that the energy added to the climate system by man-made CO2 is not only apportioned into surface warming, because a large part of the heat goes into the oceans. The rate at which surface temperatures go up is not proportional to the rate of CO2 emissions but to the cumulative total amount of atmospheric CO2. Only by looking at long-term trends - 30 years is the standard period in climate science - can we measure surface temperature increases accurately, and distinguish them from short-term natural variation.
Last updated on 10 March 2024 by John Mason. View Archives
Eclectic @50,
I have at least two questions.
1) How did they measure the aerosol density?
2) If the aerosols were created by the industrialization and they counterbalanced the CO2 effect,
how do you explain that the global temerature had been increasing from 1910 to 1940?
See figure 1 of the following thread.
http://www.skepticalscience.com/ivar-giaever-nobel-physicist-climate-pseudoscientist.html
Ken Kimura @51 , it would be best if your questions about aerosols & other drivers of climate, were kept on the one thread i.e. "CO2 is not the only driver of climate". That seems the most approriate thread; and it has the most approriate discussions in its comments column e.g. @20 and @21.
Running the same/similar questions in parallel (in different threads) is not good policy on your part. It gives the impression [ wrongly, I'm sure! ] that you may be more interested in "sloganeering" (as the moderators call it) . . . rather than in showing your genuine interest in finding information.
Similarly, your comment in the above-mentioned thread, that [your quote:] "you know that the industrialization started long before 1940" . . . does suggest [ wrongly, I'm sure! ] that you think in binary terms of industrialization being entirely absent and then on a particular date, being suddenly present at a high level of activity. Such comments by you, give the impression [ wrongly, I'm sure! ] that you prefer word games rather than science.
Good luck with your search for information & wisdom. There are some very knowledgeable people on this forum, who can help you.
Eclectic @52,
This thread and the other thread(and many others) are closely related.
And many members post their opinions into these threads.
So it is inevitable their opinions overlap.
Hence, it is also inevitable that questions to them overlap.
I don't see why asking similar questions to different members is discouraged.
People have different opinions so that their answers may differ. Knowing different answers(some may be right, some may be wrong) is usually useful for most people.
Ken @53 , there is something in what you say ~ yet you misunderstand the basic Modus Operandi of this SkepticalScience website.
When you ask a question or dispute a point, then your post will show in the Recent Comments page . . . where everyone will see it, and those who wish to reply will have the opportunity to go to your chosen thread. As a matter of course, the replies will also be funnelled through the Recent Comments page too. This way everyone can see them conveniently, and those who wish to add to / correct / or dispute those replies, will be able to do so.
So you see, that way you will get the best range of views / opinions / controversy / facts / useful links ~ all in the shortest time. And most conveniently all round.
It is a sensible & efficient arrangement ~ which is why I recommended that you keep your particular cluster of questions in one thread only. If you develop entirely unrelated questions as the discussion progresses . . . then it's best to get the first question(s) sorted out, before going on to another topic / another thread. It is best to progress step-by-step, reather than throwing up a large number of questions.
( Simultaneous multiple-pellet "shotgun" questioning is viewed poorly . . . since it's usually a sign of lack of sincerity in the poster ).
If the signal of CO2 is obscured by other forcings, then it should be possible to calculate the effect of these other forcings and remove them. What remains should be the CO2 signal (plus the signal of whatever other forcings exist that we don't know about). Cowtan's presentation does something like that for the last 20 years or so, but he says nothing about the effect of the same forcings since, say, the turn of the last century (20th century). If the warmist theory is correct, the same forcings should have been in effect for this entire time and removing them should reveal the CO2 signal. At that point one would want to look for a steady upward trend from roughly 1900 to 2015, to match the steady upward trend in CO2 emissions. Has this ever been done? And if so, where can we find the result? Thank you.
[TD] Foster and Rahmstorf created such a graph for around 1980 to 2010 (maybe it's a bit longer period than that). The general topic is called "attribution" of warming. Other studies covering the period starting around 1950 have their results shown in a bar graph on that same SkS post. See also A Comprehensive Review of the Causes of Global Warming. For details, see in the IPCC's latest report, the chapter on attribution. Humans have had a significant influence from at least 1850 to the early 20th Century, a dominant influence from then until around 1950, and have caused all the warming since at least 1975 and possibly earlier.
[TD] El Nino is removed from around 1955 through 2015, and also some other influences removed from 1970 through 2015, by Tamino.
victorag @55, I recommend you run Kevin Cowtan's 2 box model in the default settings and look at figures 4, 5, and 6. Unfortunately the data terminates with 2010, but the extra five years will make little difference.
Yes, I'm very well aware of the Foster/Rahmstorf study. The problem is that it looks very much as though they carefully selected their forcings to provide the results they needed, and appear to have applied them to a time period also predetermined to give the desired results. While a great many forcings affecting climate over the last 120 years or so have been noted in various studies, they chose to include only three, over a period of only 30 years or so. The implication is that if they included more than the carefully selected three they would not have gotten their desired result.
The only way to conduct a scientifically viable test of CO2-temp. correlation would be by systematically eliminating ALL the forcings identified over the entire period in question, i.e. at least the beginning of the 20th century.
Now if you want toclaim that CO2 is responsible for all the warming since 1975, that's a totally different matter. Are you implying that there was some sort of tipping point reached at that time, prior to which the effects of CO2 emissions were negligible? If that's the case then it would not be proper to talk about a long-term warming trend due to CO2, would it? In that case you'd be talking about a period of 25 years when temperature did in fact shoot up in tandem with CO2 emissions. But after those 25 years, the temp. increase slowed while CO2 continued to soar. How do you account for that?
I see no alternative other than the elimination or "attribution" study I suggested, where ALL forcings are taken into consideration over the entire period in question. As it seems to me such studies so far have been conducted on a piecemeal rather than comprehensive basis.
[TD] All data and code for Foster and Rahmstorf (2011) are public, so you are free to scrutinize those and run the code yourself. You are also free to modify and run their code with additional forcing data. The links I provided describe multiple other studies that you have ignored. Please read those before claiming that they do not exist. For a very thorough review, read the IPCC's AR5 Chapter 10 on Attribution.
Tom Curtis @56. Thanks for the link. Cowtan has been providing some very useful services at his websites, I must say. I find this one very interesting, but it has me puzzled. We are expected to provide a weight for each forcing, but how could one be expected to know that without being able to quantify the effects of each, and on a year by year basis. For example, the weighting for volcanic aerosols would be different from year to year, depending on volcanic activity during each year. And one would have to have access to some very reliable studies in which such year by year effects are measured. And the measurements would have to be made compatible somehow with similar year by year measurements for all the other forcings. His results seem to depend on an equal weighting for each forcing for every year, which makes no sense.
What am I missing?
I must add that I find Cowtan's graphs fascinating. Is there a paper that goes with them?
victorag, your logic behind your cherrypicking claim about Foster and Rahmstorf is invalid. The goal of Foster and Rahmstorf was to remove the influences of non-CO2 factors, to better reveal the effect of CO2. That is a straightforward procedure and logically airtight. Your claim that removing other factors somehow would hide rather than reveal CO2's effect is nonsense.
Victorag - See the numerous attribution studies listed here. As to your yearly variations issue, that's a matter of measuring the forcings and applying them with either a derived (attribution study) or best estimate (projections) of their efficacies. There is extensive literature detailing estimated forcing levels, see the information on the GISS model forcings here.
Incidentally, the use of the term "warmist" on your part leads to the perception that you frequent denial sites, and aren't really looking for the science - just so you know.
Thanks for the advise, KR. But I am at a loss to find a term characterizing those I've referred to as "warmists." I'm tempted to use "alarmists" but that's much worse, no? What would you suggest?
[PS] Lets not get offtopic with fights over labels. And in particular I would remind all parties to avoid provocative labelling. Victor I would note that "warmist" in your use would "climate scientist".
#60 No, it looks to me, Tom, as though Grant and Rahmstorf were doing the cherrypicking. What cherries do you think I picked?
[PS] Tom does not accuse you of cherry-picking. He disputes your logic by pointing out what the study sought to achieve and as such used the data available for that purpose. To continue, please state which forcings you think are missing. I would also note that a similar statistical approach was used by Benestad and Schmidt 2009 with full forcing set. That paper points out the limitations on a statistical approach as well and I would suggest a look at the larger literature on attribution as other commentators have suggested.
I would also note that taking the non-statistical approach - directly account for forcing - is what models do and you have runs covering centuries as well as studies on say ice terminatation or initiation. However, such approaches do not directly reveal CO2 influence on simple graph but as a climate sensitivity number.
victorag @58, in Kevin Cowtan's model, the year to year change in radiative forcing for each component is provided by estimates of the historical values. You can use one of two estimates, the default Meinhausen (2011) estimates, or those GISS (2011). If you leave all weightings at 1 and look at figure 3 (scaled forcings) you will see they vary year by year. What the weightings allow you to do is adjust the relative strength of the forcings if you think one or more of those forcings have been significantly under or over estimated, or if you think the impact of one or more of the forcings significantly differs from what you would expect from their radiative forcing. To take a common "skeptical" line of thought, for example, if you think the effect of WMGHG and aerosols are one tenth of that which we would estimate by radiative forcing alone, and that the solar forcing has been underestimated, we could adjust the former three (WMGHG, aerosol direct and aerosol indirect effects) to 0.2 and the latter to 2. Doing so, however, drops the coefficient of determination from 0.932 to 0.807 (and does worse things to the RMSE, although the model does not directly calculate that). That suggests that this popular 'skeptical' theory does appreciably worse at explaining the 20th century warming than does the standard IPCC account, in addition to facing significant theoretical difficulties.
As I understand it, the default (2 box) variant of Kevin Cowtan's model is a variation of that described in section 3 of Cawley et al (2015). The only significant difference as I understand it is that the model in Cawley et al uses only one time constant which makes it closer to the 1 box variant. A more complete explanation of the model as presented can be found in the Skeptical Science online course which started on Aug 9th.
victorag @57, the Foster and Rahmstorf paper uses a time period of 1979 to 2010 because the satellite temperature records start in 1979 and the paper was published in 2011 (and hence had no later data). It is difficult to describe using the full period of overlap of the temperature series they used available to them, as they did, as cherry picking with respect to time. It is possible to adopt the same approach as that in the paper over a more extended period, but the cost of so doing is that you must exclude the satellite datasets.
The three variables controlled for in the Foster and Rahmstorf model are the two known natural forcings plus the major component of natural variability. The resulting adjusted temperature therefore reflects not the temperature influence of CO2, but of the sum of all anthropogenic forcings. It may interest you to note than in discussions on his blog, Grant Foster indicated that he had tried variations of his model which also adjusted for the Pacific Decadal Oscilation and the (from memory) the Atlantic Multidecadal Oscilation and found that they had no appreciable impact (but also that you could use the PDO instead of ENSO with no appreciable impact). It is possible that the AMO was near linear over the time period dictated to Foster and Rahmstorf by their data, in which case the adjusted temperature series also includes an AMO component, but that does not sit well with measured values of the AMO:
Alternatively, you could argue that variations in the AMO closely mirror those of ENSO, and that as a consequence the ENSO adjustment in the Foster and Rahmstorf model incorporates an AMO signal into its ENSO adjustment. That being the case, the adjusted temperature series still represents the influence of the sum of anthropogenic forcings.
Finally, you could argue that there is a significant natural forcing in addition to the solar and volcanic forcing and which is not a linear function of either. In that case, the impacts of that natural forcing would also be included adjusted temperature. However, to my knowledge, no such natural forcing has been identified, and certainly no such natural forcing has been identified by the IPCC in any of their assessment reports - so Foster and Rahmstorf cannot be faulted for neglecting this purely hypothetical possibility.
Given all of this, I can see no basis for your accusation of cherry picking against Foster and Rahmstorf.
To Tom and others responding to my posts: thank you very much for your thorough commentaries, which I find very interesting and helpful. I'll need some time to consider them and will need to do a bit more reading and thinking before offering a reponse, maybe some time tomorrow.
OK, I'm back. First off I want to clarify by stressing that it was not my intention to accuse Foster and Rahmstorf of conscious deception. I have no reason to believe they were being anything other than sincere. Also, the impression I have that they were cherry picking might well be unfair. I'm not a climate scientist so it's possible there are things in their paper I do not understand.
Nevertheless it's very hard to discount the impression of cherry picking, because after all there are many more natural forcings than the three they selected, and one therefore can't help but wonder whether they were selected simply because they produced the desired result. And one also can't help wondering whether the paper would have been published at all if some other result had emerged.
While the detailed explanation very graciously provided by Tom might be perfectly valid, that does not alter the perception that confirmation bias could be at work, however unconsciously. My reaction, right or wrong, when I first read the paper was that 1. I questioned the choice of those three forcings as they appeared to be cherry picked; 2. even if we assume they were not cherry picked, one still can't help but wonder whether these same three forcings were all that were needed to correct for other discrepancies in the temperature data over a much longer time period, such as the 1940-1979 "hiatus" — and if they are not sufficient for this earlier period, why would they be sufficient for the period covered by the FR paper?
I am also wondering whether there has been any followup to the FR paper, and whether the three criteria they chose in 2010 still do the same job as convincingly when we consider the intervening years from then to now?
[PS] "Tom does not accuse you of cherry-picking. He disputes your logic by pointing out what the study sought to achieve and as such used the data available for that purpose. To continue, please state which forcings you think are missing."
I was thinking of the presentation offered on this blog by John Cook back in 2009, titled The CO2/Temperature correlation over the 20th Century ( http://www.skepticalscience.com/The-CO2-Temperature-correlation-over-the-20th-Century.html ), in which he lists 10 such forcings. It seems to me that if you are going to systematically analyze the effects of natural forcings you need to settle on the exact number of all forcings that have been identified and then apply them across the board. If certain ones have no appreciable effect during a certain period that's no excuse for excluding them — unless you want to open yourself to the perception of cherry picking. I'll add, by the way, that after all natural forcings have been identified and removed, that does not necessarily leave you with CO2, because the remainder might well be some as yet unidentified forcing, combined with CO2.
The paper by Benestad and Schmidt to which you refer is about solar forcings and, as I recall, the effect they found of solar forcings during the sharp warmup of1910-1940 is only slight. I've seen others claim that this warming period could be explained by solar forcing, but this study would seem to have refuted that theory. If in fact there is still no natural explanation for the early 20 century warmup, and CO2 levels were too low to have much effect, then it looks as though there is some as yet unidentified natural forcing that produced the warming during that period — and the same natural effect could have caused the similar extreme warmup during the period 1979-1998.
The cooling from 1940 onward, followed by a long levelling off until 1979 is also difficult to explain as the result of natural forcings, despite Cook's effort to do so. After reading through the paper by Hansen et al, on which he bases his data, the many complexities and uncertainties in the assessment of these various forcings become all too evident.
[PS] Was it that hard to just click on the Benestad and Schmidt ref? It uses all the forcings. Also note in the your Cook link that forcing are not equal and most are very minor.
The claim "The cooling from 1940 onward, followed by a long levelling off until 1979 is also difficult to explain as the result of natural forcings, despite Cook's effort to do so." verges on sloganeering if you do not provide evidence to support that, and aerosols are an anthropogenic forcing.
victorag wrote:
victorag is sloganeering, because he has failed to respond or even acknowledge my previous response in which I pointed out that "cherrypicking" is logically impossible as a label for removing only a subset of factors, when the goal of those authors was to eliminate the influence of that particular subset of factors in order to better reveal the influences of all the remaining factors. VictorAG continues to baselessly and totally irrationally claim that by eliminating only some factors it is possible to hide the influence of the remaining factors.
victorag @67 & 68:
1)
Except that if you look at Kevin Cowtan's model on the default settings, you can see that those same factors account for the 1940-1979 hiatus (Fig 1). You can also see that the response to volcanic forcings is the major natural player in the temperature increase from 1910-1940 (Fig 4), and that ENSO is a major player in flattening the temperature response in the 1940-1979 hiatus (Fig 5).
It should be noted that Cowtan's model uses the same two natural forcings, plus the same mode of natural variability as is used in Foster and Rahmstorf. Further, instead of a default assumption that any temperature response not due to those three factors is due to the sum of anthropogenic forcings, it explicitly includes those anthropogenic forcings. If a Foster and Rahmstorf's methodology would not reproduce the anthropogenic temperature response if applied over the full 1880-2010 interval, then neither should Kevin Cowtan's model produce such a good fit over that interval using the same modes of natural influence plus the explicit anthropogenic forcings.
2)
Here is are the results of the Foster and Rahmstorf adjustment updated to 2012:
For what it is worth, 2011 and 2012 saw the two strongest La Nina years since 1974/75. Since then we have had two neutral years (2014 and 2015) each of which set temperature records unadjusted, and an El Nino year which has seen unprecedented montly temperatures in the first half of the year, and is very likely to set a third annual, global record temperature in a row. Given that, it is likely that the Foster and Rahmstorf methodolog would indeed do the same job as convincingly, although I can find no update to 2015. I can, however, find an ENSO only adjustment to 2015 which supports that contention:
3)
Of the ten forcings identified by John Cook, only two are natural - solar and volcanic. The ten forcings are the same forcings as used in Kevin Cowtan's model, and if you set the model to the GISS 2011 forcings, you can even use the same dataset (extended by two years) as is used in John Cook's article. So, again "The resulting adjusted temperature [in the Foster and Rahmstorf model] therefore reflects not the temperature influence of CO2, but of the sum of all anthropogenic forcings" (see my comment @65); and again Foster and Rahmstorf use the same natural causes of variability as those used in Kevin Cowtan's model (with all 10 explicit forcings) with essentially the same result over the 1979-2010 interval (see Fig 6 of model results).
As to any unknown forcings, first in science a principle of economy is applied where we do not postulate causes without reason do do so. Foster and Rahmstorf (and Kevin Cowtan's) model show that the temperature data do not require us to postulate additional causes for the global temperature variation. Therefore if you want to postulate an additional natural source of variability, you need to show why it is necessary. You also need to provide (or find where somebody has provided) an annual index of that purported cause of variability without which the effect of the purported cause of variability cannot be tested (ie, the claim that it is a cause of variability has not been put in a falsifiable form). It is not incumbent on working scientists to chase every 'fairy at the bottom of the garden theory', but rather of the proponents of those theories to bring them into sufficiently rigorous a form that they can be tested by scientists.
Further, given the efficacy of the explanation of global temperature from 1880 onwards using the two natural, eight anthropogenic forcings plus ENSO, any postulated additional natural cause of variability must be highly correlated with one of the two natural forcing, the anthropogenic forcing, or ENSO. That would be astonishing if coincidental, and if not coincidental then the purported additional natural cause of variability has already been included de facto in the analysis. Further, if its correlation was with an anthropogenic forcing and the correlation was not coincidental, the purported additional cause would also be anthropogenic.
[PS] Thanks Tom for your considered and civil response. Victor, in the interests of maintaining civil and focused dialogue, it would be could if you could indicate where you agree or disagree with response made to you. It would especially be appreciated if you refraimed from shifting the goalposts.
Once again I want to thank everyone who responded for being so patient, so thorough and so civil. I hadn't noticed that I'd shifted the goalposts, but if that's the case I apologize. I find this dialogue extremely interesting and useful but I hope no one will mind if I persist a bit with some further questions. What I hope you will all consider is not simply the issues I've raised per se, but how questions such as these might help you to understand why some of us have remained skeptical for so long. It's not so much that I claim to understand what climate scientists are doing and reject it, as that I do not understand completely and that certain disturbing questions persist, probably because the matter at hand is so complex, but also because certain technical issues go over the heads of laymen struggling to understand. I won't attempt to deal with all the issues that have been raised, but I do have a few more questions/comments:
1. I did click on the Benestad and Schmidt paper and read much of it. I realize that many forcings were considered but what got my attention was the graph illustrating, in part, the affects of solar forcings during the early 20th century, and it looks to me as though the slope is too narrow to account for the steep temperature rise. Tom C. has claimed, above, that the response to volcanic forcings is the major factor, based on Cowtan's graphs. This is a perfect example of the sort of thing skeptics such as myself have problems with, because it's hard to see how the lack of a forcing could produce a significant warming. It seems more logical to posit some unknown forcing that could have produced this effect. And if you want to insist that there is no evidence of such a thing, my answer would be that this very dramatic runup in warming seems to be the evidence.
Secondly, I don't see how a set of graphs can in itself demonstrate anything in the absence of some sort of report explaining what they represent and how they were arrived at. Has Cowtan published on this and if so could you provide a link.
2. "The claim "The cooling from 1940 onward, followed by a long levelling off until 1979 is also difficult to explain as the result of natural forcings, despite Cook's effort to do so." verges on sloganeering if you do not provide evidence to support that, and aerosols are an anthropogenic forcing."
Where is this term "sloganeering" coming from? I don't recall offering a slogan. Have you consulted a dictionary? And yes, I can provide such evidence, in the form of a paper by James Hansen et al., published in the journal Climate Dynamics, in 2007: "Climate simulations for 1880–2003 with GISS modelE." (This was available on the Internet but as I just discovered, it no longer seems to be. Perhaps you already have a copy.) The data in this paper was the basis for the data used by Cook in his aforementioned blog post. Here is an excerpt from the abstract:
The paper, written with the assistance of 38 associates, is incredibly complex and, as the author himself acknowledges, filled with "notable discrepancies" and "deficiences," and, judging from the content generally, many uncertainties. Yet Cook picks up on data and graphs from this paper and refers to them as though they constituted reliable evidence that CO2 is "the dominant forcing" and that this data is sufficient to establish the correlation in question, i.e. the correlation between CO2 emissions and global warming. Sorry, but after skimming through the complexities of the Hansen paper, I find this pat conclusion difficult to accept.
I have one other point to make but I'll do that in a separate post.
[PS] Just to be clear: Sloganeering in my interpretation is making an assertion (the slogan) without providing supporting evidence.
When Tom answered your criticism on F&R, you suddenly jumped to another objection which is suspiciously like shifting the goal posts. A published to reference to Cowtan's works has already been given (Crawley et al).
Speaking very generally:
I've done a fair amount of research in the social sciences, especially in the areas of semiotics, ethnology, and cultural evolution, and have read extensively in the fields of psychology, archaeology, population genetics and cognitive science. And one issue that keeps coming up whenever data is being evaluated, is the issue of bias. As is well recognized in all the sciences, researchers tend to see what they expect to see, or what they want to see, and as a result many studies are tinged by confirmation bias, regardless of the intentions of the researcher, which are usually honorable.
As a result, in many fields the gold standard for any sort of testing is the controlled, double-blind experiment, where no one involved in the process has any knowledge of what's involved or any interest in the result. I realize, of course, that double-blind research is usually not possible in a field such as climate science, but that does not mean that the possibility of bias should be ignored. There is a very good reason why double-blind testing is considered so important.
I've read a great many papers by obviously qualified climate scientists that deal with the issue I've raised here, i.e., the correlation or lack of it between CO2 and warming, and while there is certainly much that I'm incapable of understanding, the impression I get is that the goal of the research in almost every case is to find some way to justify a predordained result. Thus if it's a question, say, of "accounting for" something like the so-called "hiatus," then the entire research effort is directed toward that goal, and if the goal cannot be reached then the research would be deemed pointless and would remain unpublished.
This is the impression I got from the Grant/Rahmstorf paper especially, but I get similar "vibes" from many of the others as well. While this feeling might in fact be unjustified, I do believe it goes a long way toward explaining the skepticism of so many when encountering this research, because in the absense of something like a controlled double-blind experiment it's very difficult to completely remove the suspicion of confirmation bias, even if it isn't there. It would be helpful, I think, if someone were to lobby for a different approach, where the interpretation of the data could be done by people from some other field, with no skin in the game and no preconceptions — or at least double checked by such people on a completely independent basis, so there is no possibility of influence from the primary researcher to what we could call the "control group."
When we see result after result that appears to confirm the same hypothesis, then many climate scientists see that as proof positive that "climate change is real." But a skeptic such as myself can get a very different impression, for the reasons summarized above. Rather than continually harping on the "mounds of evidence" supporting your position, which only arouse suspicions, you might do better to find some way to convince the world that your findings are the result of truly impartial and objective research rather than simply a set of foregone conclusions.
Forgive me if my remarks seem offensive, but imo these are issues you need to consider if you expect the entire world to bend to your demands.
[PS] Claims of "bending to demands" is incendary. Repeat similar and post will be deleted. It is not deleted so that other commentators are able to judge your so called serious enquiry.
If you cant fault the science demonstating the correlation when done properly, you cannot dismiss it with hand-wavy comments about how you believe science should be done. If this is wrong, then where are the alternative skeptic theories that provide better explanation?
Instead of the handwaving, once again, please state to commentators where you agree and where you disagree.
Speaking very generally:
I've done a fair amount of research in the social sciences, especially in the areas of semiotics, ethnology, and cultural evolution, and have read extensively in the fields of psychology, archaeology, population genetics and cognitive science. And one issue that keeps coming up whenever data is being evaluated, is the issue of bias. As is well recognized in all the sciences, researchers tend to see what they expect to see, or what they want to see, and as a result many studies are tinged by confirmation bias, regardless of the intentions of the researcher, which are usually honorable.
As a result, in many fields the gold standard for any sort of testing is the controlled, double-blind experiment, where no one involved in the process has any knowledge of what's involved or any interest in the result. I realize, of course, that double-blind research is usually not possible in a field such as climate science, but that does not mean that the possibility of bias should be ignored. There is a very good reason why double-blind testing is considered so important.
I've read a great many papers by obviously qualified climate scientists that deal with the issue I've raised here, i.e., the correlation or lack of it between CO2 and warming, and while there is certainly much that I'm incapable of understanding, the impression I get is that the goal of the research in almost every case is to find some way to justify a predordained result. Thus if it's a question, say, of "accounting for" something like the so-called "hiatus," then the entire research effort is directed toward that goal, and if the goal cannot be reached then the research would be deemed pointless and would remain unpublished.
This is the impression I got from the Grant/Rahmstorf paper especially, but I get similar "vibes" from many of the others as well. While this feeling might in fact be unjustified, I do believe it goes a long way toward explaining the skepticism of so many when encountering this research, because in the absense of something like a controlled double-blind experiment it's very difficult to completely remove the suspicion of confirmation bias, even if it isn't there. It would be helpful, I think, if someone were to lobby for a different approach, where the interpretation of the data could be done by people from some other field, with no skin in the game and no preconceptions — or at least double checked by such people on a completely independent basis, so there is no possibility of influence from the primary researcher to what we could call the "control group."
When we see result after result that appears to confirm the same hypothesis, then many climate scientists see that as proof positive that "climate change is real." But a skeptic such as myself can get a very different impression, for the reasons summarized above. Rather than continually harping on the "mounds of evidence" supporting your position, which only arouse suspicions, you might do better to find some way to convince the world that your findings are the result of truly impartial and objective research rather than simply a set of foregone conclusions.
Forgive me if my remarks seem offensive, but imo these are issues you need to consider if you expect the entire world to bend to your demands.
[JH] Argumentative & hyperbolic sloganeering snipped.
Hrmmm . . . yes, Victor. I have an idea. How about we get roughly 300 of the leading climate scientists together and have them work over the basic science. They'll end up creating a summary based on the existing research. Then, they can open up their summary to a series of peer reviews. Maybe two of them should be open reviews. I expect several thousand scientists would want to get involved in review. If the basic science made it out of that process still established as the overwhelmingly consensus-of-evidence strongest theory, would you elevate your level of probability for it?
"Instead of the handwaving, once again, please state to commentators where you agree and where you disagree."
I agree that the attribution of "global warming" to a variety of different forcings makes sense. I agree that such attributions involve all sorts of complexities. And I agree that climate scientists are uniquely qualified to research these complexities.
I do not agree that the picture is sufficiently clear for anyone to claim that any single forcing is a decisive factor influencing world climate. And I do not agree that simply by attempting to account for certain discrepancies by estimating the influence of specific forcings is in itself sufficient to produce a correlation between any one forcing (such as CO2) and temperature. Nor do I agree that selecting one set of forcings to account for a discrepancy during one historical period and another set when dealing with another period (as we find when we compare Grant/Rahmstorf's paper with Cook's blog post) is a valid procedure.
I also do not agree that the long list of papers intended to "account for" what looks on the surface like a lack of correlation is sufficient to produce such a correlation nevertheless. It's an open question whether each paper reinforces the previous ones or can better be seen as an attempt to correct their inadequacies. The recent paper by Karl et al. would appear to render all these older studies obsolete in any case.
More specifically, I cannot agree that any known forcings, including CO2, are capable of accounting for the dramatic temperature rise we see from 1910 to 1940. I find it difficult to accept that a rise of this magnitude could have been caused largely by the absence of volcanic activity. That strikes me as absurd. Nor can I accept that the grab bag of forcings offered by Cook can account for the cooling and leveling off we see from 1940 through the late Seventies. If CO2 emissions are a major factor in global warming then it's reasonable to assume that the signal of a steady rise in CO2 emissions during that period would be apparent in the temperature data — but no such signal is apparent, during a period of roughly 40 years.
All I can think of for now.
[PS] Thank you