Nicola Scafetta Comments on “Solar Trends And Global Warming” by Benestad and Schmidt
From Climate Science — Roger Pielke Sr.
On July 22 2009 I posted on the new paper on solar forcing by Lean and Rind 2009 (see). In that post, I also referred to the Benestad and Schmidt 2009 paper on solar forcing which has a conclusion at variance to that in the Lean and Rind paper.
After the publication of my post, Nicole Scafetta asked if he could present a comment (as a guest weblog) on the Benestad and Schmidt paper on my website, since it will take several months for his comment to make it through the review process. In the interests of presenting the perspectives on the issue of solar climate forcing, Nicola’s post appears below. I also invite Benestad and Schmidt to write responses to the Scaftta contribution which I would be glad to post on my website.
GUEST WEBLOG BY NICOLA SCAFETTA
Benestad and Schmidt have recently published a paper in JGR. (Benestad, R. E., and G. A. Schmidt (2009), Solar trends and global warming, J. Geophys. Res., 114, D14101, doi:10.1029/2008JD011639).
This paper criticizes the mathematical algorithms of several papers that claim that the temperature data show a significant solar signature. They conclude that such algorithms are “nonrobust” and conclude that
“the most likely contribution from solar forcing a global warming is 7 ± 1% for the 20th century and is negligible for warming since 1980.”
By using the word “robust” and its derivates for 18 times, Benestad and Schmidt claim to disprove two categories of papers:
those that use the multilinear regression analysis [Lean and Rind, 2008; Camp and Tung, 2007; Ingram, 2006] and those that present an alternative approach [Scafetta and West, 2005, 2006a, 2006b, 2007, 2008]. (See the references in their paper.)
Herein, I will not discuss the limitation of the multilinear regression analysis nor the limits of Benestad and Schmidt’s critique to those papers. I will briefly focus on Benestad and Schmidt’s criticism to the papers that I coauthored with Dr. West. I found Benestad and Schmidt’s claims to be extremely misleading and full of gratuitous criticism due to poor reading and understanding of the data analysis that was accomplished in our works.
Let us see some of these misleading statements and errors starting with the less serious one and ending with the most serious one:
1. Since the abstract Benestad and Schmidt claim that they are rebutting several our papers [Scafetta and West, 2005, 2006a, 2006b, 2007, 2008]. Already the abstract is misleading. Indeed, their criticism focuses only on Scafetta and West [2005, 2006a]. The other papers used different data and mathematical methodologies.
2. Benestad and Schmidt claim that we have not disclosed nor detailed the mathematical methodology and some parameters that we use. For example:
a) In paragraph 39 Benestad and Schmidt criticize and dismiss my paper with Willson [2009] by claiming that we “did not provide any detailed description of the method used to derive their results, and while they derived a positive minima trend for their composite, it is not clear how a positive minima trend could arise from a combination of the reconstruction of Krivova et al. [2007] and PMOD, when none of these by themselves contained such a trend).” However, the arguments are quite clear in that paper and in the additional figures that we published as supporting material. Moreover, it is not clear to me how Benestad and Schmidt could conclude that our work is wrong if Benestad and Schmidt acknowledge that they have not understood it. Perhaps, they just needed to study it better.
b) In paragraph 41 Benestad and Schmidt claim that: “It is not clear how the lagged values were estimated by Scafetta and West [2006a]“. However, in paragraph 9 of SW06a it is written “we adopt the same time-lags as predicted by Wigley’s [1988, Table 1] model.” So, again, Benestad and Schmidt just needed to study better the paper that they wanted to criticize.
c) In paragraph 48 Benestad and Schmidt claim that: “over the much shorter 1980-2002 period and used a global surface temperature from the Climate Research Unit, 2005 (they did not provide any reference to the data nor did they specify whether they used the combined land-sea data (HadCRUT) or land-only temperatures (CRUTEM).” However, it is evident from our work SW05 that we were referring to the combined land-sea data which is properly referred to as “global surface temperature” without any additional specification (Land or Ocean, North or South). We also indicate the webpage where the data could be downloaded.
d) In paragraph 57 Benestad and Schmidt claim that: “The analysis using Lean [2000] rather than Scafetta and West’s own solar proxy as input is shown as thick black lines.” However, in our paper SW06a it is crystal clear that we too use Lean’s TSI proxy reconstruction. In particular we were using Lean 1995 which is not very different from Lean 2000. Benestad and Schmidt apparently do not know that since 1978 Lean 1995 as well as Lean 2000 do not differ significantly from PMOD because PMOD was build (by altering the published TSI satellite data) by using Lean 1995 and Lean 2000 as guides. Moreover, we also merge the Lean data with ACRIM since 1978 to obtain an alternative scenario, as it is evident in all our papers. The discontinuity problem addressed by Benestad and Schmidt in merging two independent sequences (Lean’s proxy model and the ACRIM) is not an issue because it is not possible to avoid it given the fact that there are no TSI satellite data before 1978.
3. In Paragraphs 48-50 Benestad and Schmidt try to explain one of our presumed major mathematical mistakes. Benestad and Schmidt’s states: “A change of 2*0.92 W/m2 between solar minimum and maximum implies a change in S of 1.84 W/m2 which amounts to 0.13% of S, and is greater than the 0.08% difference between the peak and minimum of solar cycle 21 reported by Willson [1997] and the differences between TSI levels of the solar maxima and minima seen in this study (~1.2 W/m2; Figure 6).” Benestad and Schmidt’s are referring to our estimate of the amplitude of the solar cycle referring to the 11-year modulation that we called A7,sun = 0.92 W/m2 in SW05. Benestad and Schmidt are claiming that our estimate is nor reasonable because in their opinion according to our calculations the change of TSI between solar maximum and solar minimum had to be twice our value A7,sun , so they write 2*0.92=1.84 W/m2, and this would be far too large. However, as it is evident from our paper and in figure 4a in SW05 the value A7,sun refers to the peak-to-trough amplitude of the cycle, so it should not be multiplied by 2, as Benestad and Schmidt misunderstood. This is crystal clear in the factor ½ before the equation f(t)= ½ A sin(2pt) that we are referring to and that Benestad and Schmidt also report in their paragraph 48. It is hard to believe that two prominent scientists such as Benestad and Schmidt do not understand the meaning of a factor ½! So, again, Benestad and Schmidt just needed to think more before writing a study that criticizes ours.
4) Finally, Benestad and Schmidt’s paper is full of misleading claims that they are reproducing our analysis. Indeed, Benestad and Schmidt’s paper is self-contradictory on this crucial issue. In paragraph 85 Benestad and Schmidt claim that they “have repeated the analyses of Scafetta and West, together with a series of sensitivity tests to some of their arbitrary choices.” However, in their paragraph 76 Benestad and Schmidt acknowledge: “In our emulation, we were not able to get exactly the same ratio of amplitudes, due to lack of robustness of the SW06a method and insufficient methods description.” It is quite singular that Benestad and Schmidt claim to have repeated our calculation, at the same time they acknowledge that, indeed, they did not succeed in repeating our calculation and, ironically, they blame us for their failure. It is not easy to find in the scientific literature such kind of tortuous reasoning!
In fact, the reason why Benestad and Schmidt did not succeed in repeating our calculation is because they have misapplied the wavelet decomposition algorithm known as the maximum overlap discrete wavelet transforms (MODWT). This is crystal clear in their figures 4 where it is evident that they applied the MODWT decomposition in a cyclical periodic mode. In other words they are implicitly imposing that the temperature in 2001 is equal to the temperature in 1900, the temperature in 2002 is equal to the temperature in 1901 and so on. This is evident in their figure 4 where the decomposed blue and pink component curves in 2000 just continue in 1900 in an uninterrupted cyclical periodic mode as shown in the figure below which is obtained by plotting their figure 4 side by side with itself:
Any person expert in time series processing can teach Benestad and Schmidt that it is not appropriate to impose a cyclical periodic mode to a non stationary time series such as the temperature or TSI records that present clear upward trends from 1900 to 2000. By applying a cyclical periodic mode Benestad and Schmidt are artificially introducing two large and opposite discontinuities in the records in 1900 and 2000, as the above figure shows in 2000. These large and artificial discontinuities at the two extremes of the time sequence disrupt completely the decomposition and force the algorithm to produce very large cycles in proximity of the two borders, as it is clear in their figure 4. This severe error is responsible for the fact that Benestad and Schmidt find unrealistic values for Z22y and Z11y that significantly differ from ours by a factor of three. In their paragraph 50 they found Z22y = 0.58 K/Wm-2, which is not realistic as they also realize later, while we found Z22y = 0.17 K/Wm-2, which is more realistic.
This same error in data processing also causes the reconstructed solar signature in their figures 5 and 7 to present a descending trend minimum in 2000 while the Sun was approaching one of its largest maxima. Compare their figures 4a (reported above), 5 and 7 with their figure 6 and compare them also with our figure 3 in SW06a and in SW08! See figure below where I compare Benestad and Schmidt’s figures 6 and 7 and show that the results depicted in their Figure 7 are non-physical.
Because of the severe and naïve error in applying the wavelet decomposition, Benestad and Schmidt’s calculations are “robustly” flawed. I cannot but encourage Benestad and Schmidt to carefully study some book about wavelet decomposition such as the excellent work by Percival and Walden [2000] before attempting to use a complex and powerful algorithm such as the Maximum Overlap Discrete Wavelet Transform (MODWT) by just loading a pre-compiled computer R package.
There are several other gratuitous claims and errors in Benestad and Schmidt’s paper. However, the above is sufficient for this fast reply. I just wonder why the referees of that paper did not check Benestad and Schmidt’s numerous misleading statements and errors. It would be sad if the reason is because somebody is mistaking a scientific theory such as the “anthropogenic global warming theory” for an ideology that should be defended at all costs.
Nicola Scafetta, Physics Department, Duke University
SSam (17:24:07) :
Out on a limb here given the current discussion, but some of the topic makes me ask if the is a way to determine how much radiant heating comes from the photosphere (the observable disk) at ~5,778 K and ~32 arc minutes verses the corona at ~5×106 K, which covers a highly variable but comparable angular segment of the sky?
That’s precisely what I am referring to. The effective temperature of the photosphere is not so high (relatively); it’s 5800 K. Nevertheless, the temperature of the interplanetary medium (IPM) above the Corona is 100000 K. This temperature decreases as the distance from the Sun increases, i.e. it decreases in an inverse proportion to the square of the distance from the Sun to the explored system.
Leif Svalgaard (17:36:40):
In your response to Jeff Id (16:30:22) you forgot to mention that the correlation coefficient between the proportion of HSG and the TSI is higher from your reconstruction than from Lean’s reconstruction. 🙂
SSam (17:24:07) :
how much radiant heating comes from the photosphere (the observable disk) at ~5,778 K and ~32 arc minutes verses the corona at ~5×106 K, which covers a highly variable but comparable angular segment of the sky?
A total solar eclipse gives you a good shot at this. The corona radiates about a million times less than the photosphere.
Because the solar wind is so thin the amount of heat in it is negligible.
Mark T (17:30:11) :
We (the signal processing community) have had plenty of time to understand and incorporate wavelet analysis methods into our general framework.
The same goes for every other discipline I know of [perhaps with the notable exception of ecology]. Perhaps the general public is less up-to-date than the scientific community, so some outreach might be important.
Nasif Nahle (17:54:27) :
In your response to Jeff Id (16:30:22) you forgot to mention that the correlation coefficient between the proportion of HSG and the TSI is higher from your reconstruction than from Lean’s reconstruction. 🙂
I apparently don’t need to 🙂
but in general, just because it fits better does not mean it is better. The reconstruction has to stand on its own merit [or lack thereof].
Leif Svalgaard (18:10:17) :
Mark T (17:30:11) :
We (the signal processing community) have had plenty of time to understand and incorporate wavelet analysis methods into our general framework.
The same goes for every other discipline I know of [perhaps with the notable exception of ecology]. Perhaps the general public is less up-to-date than the scientific community, so some outreach might be important.
Wavelet analysis methodologies have been incorporated to evolutionary ecology and paleoecology. I don’t know why the modern ecology is a solid block resistant to progress. Perhaps because it has been sequestered by other non factual disciplines?
In their 2006 paper, Scafetts and West conclude:
“Thus, if it happens that a TSI proxy reconstruction with small secular variability such as Lean2005 better represents the historical TSI evolution, the logical conclusion would be that the climate secular feedback to TSI change and/or alternative solar effects on climate (such as UV and cosmic ray change effects) are much stronger than what would occur if other TSI reconstructions with larger secular variability would more faithfully represent the real TSI evolution.”
Now, let me go the next step: with a TSI reconstruction [such as mine] with NO secular variability, their logical conclusion would be that the climate secular feedback to TSI change is extremely much [in the limit infinitely] stronger. This was my original reason to comment on blogs [started out at Tamino’s – and was banned; then ClimateAudit where the discussion ran to 4000 posts without any progress; and now here, still without any real resolution of the problem], because I was asking the ‘climate people’ [I thought] if they could help me understand such hypersensitivity, which would likely lead to runaway [yet the long-term climate is stable within narrow bounds].
Leif,
For TSI, I see you reconstructed it using geomagnetic data. Am I understanding correctly that you modified sunspot records over time by the geomagnetic Y component to correct for reduced historic observation acuity in comparison to the present?
Nasif,
I just read an online article about your comment above after a google search and understand your point.
Jeff Id (19:00:32) :
For TSI, I see you reconstructed it using geomagnetic data. Am I understanding correctly that you modified sunspot records over time by the geomagnetic Y component to correct for reduced historic observation acuity in comparison to the present?
Partly. Rudolf Wolf who invented the sunspot number used the geomagnetic record to ‘splice’ together records from different observers. His successors either forgot or dismissed this objective technique with the result that the sunspot number calibration suffered. We presented the following at the Solar Physics Divisions meeting in June:
The Waldmeier Discontinuity [Recalibration of the Zurich Sunspot Number]
Leif Svalgaard (Stanford), Luca Bertello (UCLA), & Edward W. Cliver (AFRL)
“When Max Waldmeier took over the production of the Sunspot Number, Rz, in Zurich in 1945 he was relatively inexperienced in the art of divining sunspot numbers [Friedli, 2005] and he feared that the sunspot numbers may not have had the same calibration as the existing series produced by the previous Zurich observers. We suggest that his fear was not unfounded and that the Zurich sunspot number be increased by 20% to match the modern record. In this poster we explore three reasons and methods on which we base this conclusion.
(1) The range of the diurnal variation of the East-component of the geomagnetic field controlled by FUV-induced conductivity of the day-side ionosphere is a strong proxy for solar activity, as already Rudolf Wolf had noted in 1856, and indicates a 22% increase of the sunspot number from 1946 onwards.
(2) The Greenwich Sunspot Areas (and the Group Sunspot Number, Rg, largely derived from the areas) indicate a 17.5% increase of Rz coincident with Waldmeierís tenure.
(3) The Ca II K-line index [see poster 15.16 by Bertello et al.] indicate a 20% increase in Rz around 1946.
Of course, it would be more convenient to increase the pre-1946 numbers by a similar amount rather than change the modern numbers which may be ingredients in operational forecast techniques.”
Paper here: http://www.leif.org/research/SPD-2009.pdf
The other [and more significant] departure is the lack of evidence of a secular trend in TSI at sunspot minima
————-
We realize it will be a long hard slug to turn this ship around. The solar community might be a lot easier to convince [at least judging from the comments at the meeting] than the climate ‘researchers’ [of both stripes] that want/need a solar connection.
Leif Svalgaard (18:36:07) :
Leif Svalgaard (18:36:07) :
Nasif Nahle (17:54:27) :
In your response to Jeff Id (16:30:22) you forgot to mention that the correlation coefficient between the proportion of HSG and the TSI is higher from your reconstruction than from Lean’s reconstruction. 🙂
I apparently don’t need to 🙂
but in general, just because it fits better does not mean it is better. The reconstruction has to stand on its own merit [or lack thereof].
The theory of truth compels theorists to be coherent with other related theorists. Although I agree with your feeling on no needing to mention it because you feel your theory is robust alone, other theorists could feel the need of mentioning this correlation, true?
On your other opinion about your failure to bring the debate onto the intensification of the solar signal by the Earth thermal system, I think you’re not being fair in your judgment… I don’t like to get myself personal, however, for a first and last occasion, I think you have not been enough clear on your purpose. I am sure people here have gotten the idea and are trying to find the mechanism. Don’t you think so?
By the way, do you know why river quartz grains are more susceptible to insolation than sea quartz grains? Perhaps the answer to the big question resides in this humble phenomenon.
I love the off topic stuff…
noaaprogrammer (11:12:23) : you said…
“Having interacted with college students since I first began teaching them in 1970, I assert that they generally sort themselves along the left/right political axis as follows: The students in the numerical-oriented majors such as business, science, engineering, mathematics, computer science, etc., generally tend toward the right end of the political spectrum, while the non-numerical oriented students in the humanities tend toward the left end.”
Your observation is undoubtedly true, however, students eventually self select different paths. Those heading to the Ph.D. tend toward left politics, while the right tending typically leave after B.Sc. or M.Sc. and head toward business and industry.
The climate bill thread here points to an article that states…
“according to press reports, EPA is projecting this legislation would take 56 million crop acres out of production due to afforestation.”
This would be more humorous if it didn’t illustrate how the government wastes time and money. Exactly how are we to meet the administration’s targets on ethanol production, which requires a hundred million acres of new cropland when congress is writing legislation that takes such out of production?…the two arms of government like those of Dr. Strangelove …
Correction: I wrote in my post Nasif Nahle (19:35:02)
“Leif Svalgaard (18:36:07):
Leif Svalgaard (18:36:07):”
It should have been as follows:
“Leif Svalgaard (18:36:07):
Leif Svalgaard (18:56:20):”
I apologize… 🙁
Nasif Nahle (19:35:02) :
I think you have not been enough clear on your purpose. I am sure people here have gotten the idea and are trying to find the mechanism. Don’t you think so?
Frankly, no. As long as they can beat down AGW, it doesn’t matter how or with what, true or false – as long as it works.
My purpose was set out clearly here: http://www.climateaudit.org/?p=2470
By the way, do you know why river quartz grains are more susceptible to insolation than sea quartz grains?
No, perhaps you could explain why any grain is susceptible to insolation in the first place…
Leif, a couple of questions about the slide:
http://www.leif.org/research/TSI-LEAN2008.png
I thought you previously stated that sunspot activity during the 19th century was as intense as the 20th. Is the graph incorrect?
What caused the spike in TSI near the end of 2003?
Nasif and Leif,
I’ve been reading Leif’s links and have read one from Nasif I found by google search. The theory that sunspots were underestimated makes sense but as an engineer I cannot determine the quality of the data from these links.
I’m left with the impression that it’s a plausible and even likely correction to the data but there isn’t enough information in the links to give me certainty. How good were the magnetic measurements over 100 years ago? Are they better than the ridiculously overreaching global temp records from that time frame?
Leif , I think your poster paper, discussed at (19:21:43), answered my first question.
Tom in Texas (19:51:24) :
I thought you previously stated that sunspot activity during the 19th century was as intense as the 20th. Is the graph incorrect?
You could say that. Lean is using the Group Sunspot Number which is different from the Zurich number and need a larger correction, see: http://www.leif.org/research/CAWSES%20-%20Sunspots.pdf
What caused the spike in TSI near the end of 2003?
Two very large sunspot groups that took a bite out of TSI.
ftp://howard.astro.ucla.edu/pub/obs/drawings/2003/dr031029.jpg
Jeff Id (19:52:16) :
How good were the magnetic measurements over 100 years ago?
they were good enough [and even 100 years before that they were OK]. The measurements are of an angle, and the variation is of the order of 10 arc minutes which could be easily measured, Bradley discovered the 20 arc second aberration in 1725. Also, the figure on page 11 of http://www.leif.org/research/Napa%20Solar%20Cycle%2024.pdf shows the declination at Prague measured in 1840-1849 compared to modern measurements at the same place. As you can see, even minute wiggles are the same in both plots. So the measurements are of good quality and are not in doubt [by anybody].
tallbloke,
You might want to check out Figure 2 (SOLID GOLD) in:
Trenberth, K.E. & Stepaniak, D.P. (2001). Indices of El Nino Evolution. Journal of Climate 14, 1697-1701.
http://www.cgd.ucar.edu/cas/Trenberth/trenberth.papers/tniJC.pdf
This relates to:
1) our earlier discussion (including the phase relations plots I posted).
2) Tsonis, A.A.; Swanson, K.; & Kravtsov, S. (2007). A new dynamical mechanism for major climate shifts. Geophysical Research Letters 34, L13705.
http://www.uwm.edu/~aatsonis/2007GL030288.pdf
3) Zolotova’s, Charvatova’s, Sidorenkov’s, & Vangeneim’s work.
4) Bob Tisdale’s graph:
http://i35.tinypic.com/166wxnk.jpg
Also – Figure 3 in:
Keeling, C. D. & Whorf, T. P. (1997). Possible forcing of global temperature by the oceanic tides. Proceedings of the National Academy of Sciences of the USA 94(16), 8321-8328.
http://www.pnas.org/content/94/16/8321.full.pdf?ijkey=YjbRA3bMQaGic
–
Re: Nasif Nahle (17:35:04)
I’m with you on insolation & depth.
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Re: Mark T (17:30:11)
Thanks for the note. I spent the last 6 years working for a statistics department and only encountered 1 brief mention of wavelets aside from my own work. (Regrettably, tradition is acting as a (20 year) brake in some corners. It’s an uphill battle fighting stubborn convention.)
–
tallbloke,
I’ve run into the argument that aa is confounded with UV which affects LOD. The physicists can argue about such things; in the meantime I’ll run analyses with multiple datasets when there are controversies and state conclusions with a full set of qualifiers [in anything formal].
You might find the following interesting:
http://syrte.obspm.fr/journees2005/s2_12_Chapanov.pdf
http://syrte.obspm.fr/journees2007/PDF/s4_18_Chapanov.pdf
http://pecny.asu.cas.cz/cedr/download/chapanov1a.pdf
(I’m not suggesting these works are final products.)
–
John S. (16:56:10) “[…] The effect is much like the centerfold […]”
An institution for which I once worked once published against my will a very long article full of very colorful wavelet & time-integrated cross-correlation plots, even though the article was not even remotely ready for press. (I did not sign the consent forms.) You are right: People are eager to use the attractive plots. I am concerned that this will cause a backlash against good plots (coming from people who wouldn’t know a good wavelet or time-integrated cross-correlation plot from a bad one, but who are otherwise very dignified, educated, & intelligent …and thus formidable opponents politically & administratively).
Leif Svalgaard (19:45:45):
By the way, do you know why river quartz grains are more susceptible to insolation than sea quartz grains?
No, perhaps you could explain why any grain is susceptible to insolation in the first place…
Now it was me who wasn’t enough clear. It’s a bit complicated, though. If I compare the proportions of HSG of sea samples with riverbed samples, the latter show a higher percentage of stained quartz, almost all samples show proportions above 11%, than sea samples.
I have also have found, preliminarly, that the sea samples contain greater amounts of magnetite, gold and other minerals. Perhaps it is the explanation (?).
Jeff Id (19:52:16) :
Nasif and Leif,
I’ve been reading Leif’s links and have read one from Nasif I found by google search. The theory that sunspots were underestimated makes sense but as an engineer I cannot determine the quality of the data from these links.
I’m left with the impression that it’s a plausible and even likely correction to the data but there isn’t enough information in the links to give me certainty. How good were the magnetic measurements over 100 years ago? Are they better than the ridiculously overreaching global temp records from that time frame?
I’m able to respond on my work. My databases were taken from the assessment of Dr. Bond and colleagues, which coincides with the investigations of other geologists and paleobiologists.
I didn’t correct the last figure (labeled like “Today”) from Dr. Bond’s database when I was writing the article, though I’ve found a percentage higher than that of Dr. Bond. As an interim measure, it is 6.25% for the most recent layer.
The solar variability debate is not really settled. Leif’s arguments seem reasonable and those pointing to more variability are also reasonable.
We do know that the Sun is a variable star. It has at least a 9-13 year cycle. It may also vary by larger amounts on longer time-scales, it might not, it may skip cycles, it might have weaker cycles every now and again, it might make no difference anyway. But it is a remarkably stable variable star.
What we do know is that it is acting out of character right now – at least out of the character that we are certain about. The effect might be so small we will not notice any climate changes at all from it or it could be as much as a few tenths of degree C change.
My neighbors know that this is coldest below normal 8 month period we have had on record. Other places are warmer of course. I’m okay with it being warmer. I’m good with a Sun perking up a little. If not, I’m okay with global warming, I just wish it would finally show up.
From 10Be cosmic ray fluxes Steinhilber et al. reports:
http://www.leif.org/EOS/Holocene-TSI.pdf
that
“The entire record of TSI covering the past 9300 years is shown in Figure 3. Throughout this period TSI has varied by approximately 2Wm−2”
This extreme variation was reached only rarely and most of the time TSI stays within +/-0.5 w/m2 of average. A variation much lower than normally assumed in climate studies.
Bill Illis (20:40:49) :
The solar variability debate is not really settled. Leif’s arguments seem reasonable and those pointing to more variability are also reasonable.
Which other ones?
It seems that my short article is attracted the attention of many people! I would like to thank you for your comments.
I just would like to briefly address a comment from Leif Svalgaard.
Leif is claming that TSI did not change on a secular scale, more precisely he claims that at each minima TSI reaches the same value.
The secular TSI reconstruction by Leif contrasts with those proposed by all other authors (Lean, Hoyt, Solanki, Lockwood etc) that present a certain degree of secular solar variability. Indeed, all these TSI proxy reconstructions present different amplitudes of the secular trends.
Personally, I believe that nobody (Leif as well as everybody else) can be 100% sure about the secular TSI behavior. The reason is quite simple, we just do not have secular TSI data against which testing the TSI proxy reconstructions nor we have complete and rigorous dynamical solar models that predict the solar behavior. So, everybody can say more or less whatever he wants.
The real problem is whether a proposed TSI is reasonable or not.
Personally, I do not believe that TSI does not present secular trends as Leif claims. The reason is because it is not easy that a turbolent system such as the sun returns always at the same “exact” value at each minima. Of course, the above is not the “scientific” prove that Leif’s TSI is erroneous. We just do not have TSI data about the past to scientifically test the hypothesis.
The things are different if we look at the last decades when direct satellite TSI observations are available. Although there exists a controversy between PMOD and ACRIM about the relative position of the TSI minima in 1986 and 1996, all experimental TSI satellite groups agree about the fact that the current TSI minimum is well below the minimum in 1996.
See for example the violet daily TSI satellite data in the figure reported in
http://www.leif.org/research/TSI-LEAN2008.png
The violet daily TSI satellite data indeed look like ACRIM composite: the nimimum in 1996 is higher than the minima in 1986 and 2008.
Again, the above does not disproves Leif’s proxy TSI reconstruction, because there may be the possibility that all experimental TSI satellite groups (ACRIM, PMOD, TIM etc.) are wrongly reporting the correct TSI value! However, from a purely scientific point of view (that is, a theory is scientific if and only if it is supported by some data) right now Leif’s proxy TSI reconstruction is contradicted by the above experimental finding. Also other TSI proxy reconstructions such as Lean’s ones are contradicted by the above finding.
So, I believe that Leif should do his best to convince all experimental TSI groups to correct their published satellite TSI data by proving them exactly where their detectors and/or algorithms are failing. Until then, I believe that we need to look at the TSI data for what they say. What they right now say is that TSI presents multidecadal trends that the current TSI proxy models fail to reproduce. Thus, in my opinion most of the effort should be in trying to develop better solar models.
Nicola Scafetta (21:30:21) :
Leif is claming that TSI did not change on a secular scale, more precisely he claims that at each minima TSI reaches the same value.
Not exactly. TSI reaches a value determined by the residual solar activity which is not zero. It is even possible that the open magnetic flux determines TSI. My claim is that there is no other long-term, secular trends over and above the open flux, e.g. as given by the Heliospheric Magnetic Field. The HMF can be reliably determined back to 1882 and with somewhat greater uncertainty back to 1835 and shows no secular trend, specifically HMF in 1901-1902 is just what it is right now, thus TSI should be the same then as now.
The argument that we can only use the TSI we have actually measured invalidates the Phenomenological Method of determining climate sensitivity based on the TSI we have not measured.