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ACRIM vs PMOD

Filed under: — rasmus @ 6 May 2009 - (Italian)

Two recent papers (Lockwood & Fröhlich, 2008 – ‘LF08′; Scafetta & Willson, 2009 – ‘SW09′) compare the analysis of total solar irradiance (TSI) and the way the TSI measurements are combined to form a long series consisting of data from several satellite missions. The two papers come to completely opposite conclusions regarding the long term trend. So which one (if either) is right, then? And does it really matter?

This issue is a very familiar one when it comes to long-time series from satellite data. Each individual satellite only lasts a few years, and so a 30 year time series needs to be stitched together from a series of satellites. Each of those instruments might have a different calibration, and may have non-climatic drifts associated with instrument degradation, or orbital effects. Thus it can often be the case that there is a degree of ambiguity in putting together the series. This issue is at least part of the difference between the RSS and UAH tropospheric temperature trends, and in the CERES/ERBE analyses discussed recently.

The differences between PMOD and ACRIM have already been discussed by the SkepticalScientist and Tamino, so here is just an update in the light of the two recent papers. The important issue here is the so-called ‘ACRIM-gap’, the time between the ACRIM-I instrument ceased and when the ACRIM-II observations started (mid-1989 to late 1991), and how the data from these two instruments are combined using other overlapping observations. Note that the ‘ACRIM’ name for the Willson et al time-series simply implies that it was put together by some people on the ACRIM science team, not that they use different satellite data.

The focus on these papers is what the ‘ACRIM gap’ implies for TSI levels during the solar minimum at solar cycles 21 and 22. Whereas PMOD suggests that the TSI levels during these minima are similar, ACRIM suggests that the TSI level is higher during the minimum of cycle 22. SW08 even claim that there has been a positive ‘minima trend‘.

LF08 conclude that the PMOD is more realistic, since the change in the TSI levels during the solar minima, suggested by ACRIM, is inconsistent with the known relationship between TSI and galactic cosmic rays (GCR). It is well-known that the GCR flux is generally low when the level of solar activity is high, because the solar magnetic fields are more extensive and these shield the solar system against GCR (charged particles). However the two effects don’t always go in lockstep, so this is suggestive rather than conclusive.

It is also clear from the instrumental data that the TSI tends to increase with the solar activity level – at least over the solar cycle. LF08 argue that if the ACRIM ‘minimum trend’ is correct, this will mean that past reconstruction of TSI based on e.g. sunspots are incorrect, and a lot of studies on the past climate variations would be wrong. This does not mean that the ACRIM data are useless, but that there are uncertainties regarding the relationship TSI-levels, solar activity for different time scales.

I found insufficient detailed description in SW09 of the methodology used in their analysis to be able to judge the real merit of their work. The paper provides a link to auxiliary material that does not work. However, the figures in the paper don’t really convince when I don’t know how they were made.

Furthermore, I found the SW09 a bit confusing, as it gives the impression that the PMOD composite relies on ERBS/ERBE data during the ACRIM-gap (“The PMOD team uses the sparse ERBS/ERBE data base to ‘bridge’ the ACRIM gap, conforming the higher cadence Nimbus 7/ERB to it by making adjustments due to …”). However the information in LF08 says PMOD used HF from Nimbus 7 (ERB).

The PMOD analysis involves an adjustment to correct for a glitch in the ERB data (orientation changes and/or switching off), but SW09 claims – without providing convincing arguments – that this correction cannot be justified.

The ACRIM composite does not account for a jump in the ‘ACRIM-gap’ due to instrumental changes. SW09 show a comparison between different analyses and Krivova et al. (2007) modeled TSI, but later acknowledge that the latter modeled TSI disagrees with measurements on decadal time scales. Furthermore, when the TSI is not adjusted over the ‘ACRIM-gap’, there is the apparent inconsistency between TSI and GCR.

Update: My conclusion is that the LF08 paper is far more convincing than the SW09 in terms of whether the TSI data should be adjusted over the ‘ACRIM-gap’. But the this is probably not the final word on the matter.


96 Responses to “ACRIM vs PMOD”

  1. 1

    Hmm… so does it really matter?

  2. 2
    pascal says:

    Hi Rasmus

    There is inconsistency between ACRIM reconstruction during the 22 minimum and the GCR, OK, but also with radio flux and SSN.
    It is not the case for PMOD.
    When we look at the to-day situation at the beginning of 24 cycle, the correlation between SSN, PMOD TSI, and radio flux is good, so, why should’nt it be during 22 minimum?

  3. 3
    Giovanni Pellegrini says:

    The link to supplementary materials appears now to be working. It contains original figure files, and a probably more interesting statement from Douglas Hoyt.

    Best Regards

    [Response: Link here. - gavin]

  4. 4
    Mark says:

    If two papers come to different conclusions then each should find out what is wrong in the other.

    After that, pass these comments back. See what changes come up. If they still disagree and point different directions, then there is no conclusion.

    Neither are right. The long term trend is officially a known unknown.

  5. 5
    CM says:

    Is it significant?

    From the SW09 abstract:

    Both ‘mixed’ composites demonstrate a significant TSI increase of 0.033 %/decade between the solar activity minima of 1986 and 1996, comparable to the 0.037 % found in the ACRIM composite.

    The IPCC AR4, 2.7.1.2.2:

    In terms of plausible physical understanding, the most
    likely secular increase in total irradiance from the Maunder
    Minimum to current cycle minima is 0.04% (an irradiance
    increase of roughly 0.5 W m^-2 in 1,365 W m^-2), corresponding
    to an RF of +0.1 W m–2. (…) Since the 11-year cycle amplitude has increased from the Maunder Minimum to the present, the total irradiance increase to the present-day cycle mean is 0.08%.

    Does this mean the decadal increase claimed by SW09 is on the same order as the whole TSI increase since the Maunder minimum? Or am I missing something?

  6. 6
    Christopher Hogan says:

    It might be helpful to state what the two different trends imply for solar forcing over the past few decades or so. For the lay audience like myself, who might not know that. In other words, how significant is the discrepancy for interpreting the current warming?

    Your reference to SkepticalScientist told me what I wanted to know. They say: “Regardless of which dataset you use, the trend is so slight, solar variations can at most have contributed only a fraction of the current global warming.” Might be worth having that said here (if you agree), to frame the issue a bit more.

  7. 7
    manu says:

    CM #5 : According to the authors, it should indeed be significant (provided they’re right ;-) ). They conclude with:

    “This finding has evident repercussions for climate change and solar physics. Increasing TSI between 1980 and 2000 could have contributed significantly to global warming during the last three decades [Scafetta and West, 2007, 2008]. Current climate models [Intergovernmental Panel on Climate Change, 2007] have assumed that the TSI did not vary significantly during the last 30 years and have therefore underestimated the solar contribution and overestimated the anthropogenic contribution to global warming.”

  8. 8
    tamino says:

    My post on PMOD vs ACRIM is the first of two; more relevant to the comparison of those two reconstructions is the second post, here.

  9. 9
    tjlyerly says:

    Seems to me this focus only on TSI and the slight changes from minima to
    maxima and over the decades (and the slight impact this may have on climate)
    misses the point.

    What I want to understand, and this is not something I’ve seen covered very
    well in any paper I’ve seen, is how the distribution of the spectrum of
    wavelength of radiation from the sun has changed over time. Both from solar max
    to min and from one cycle to the next – and how this spectrum is changing in
    the current minimum, which is certainly unusual at least in modern terms.

    Gavin – I believe you co-authored a paper stating that the UV spectrum during
    solar minimum decreases by (at least) 6% during minimum. How does this affect global
    cloud cover, assuming Cosmic Rays are not an important factor. What about other
    wavelengths? How does this change in the spectrum affect absorption and
    reflectivity in the atmosphere and in the groundcover/oceans?

    There have been other studies done that show that cloudcover (and the earth’s
    albedo) increase during solar minimum. What is the mechanism that causes this
    and how would this be affected by a prolonged solar minimum which is certainly
    possible given the unusual things the sun is doing now?

  10. 10
    Lynn Vincentnathan says:

    Now let me get this straight (correct me if I’m wrong):
    – The sun goes thru cycles between solar minima and solar maxima (activies, like flares and sunspots) & with the solar minima we’d have less TSI, and with the maxima we’d have more TSI.
    – The solar maxima would warm the earth a bit (or is it the TSI that’s warming it a bit?), and the solar minima would cool the earth a bit.
    – We apparently are in a solar minima right now, so ergo the earth should be cooling, all other things being equal, which they are not.
    – AGW denialists think somehow that being in a solar minima disproves AGW, even tho we’re not (from what I understand) cooling down as much as would be expected, and are actually warming up.
    – AGW denialist just can’t wait for the solar minima to end, and the solar maxima upswing to begin, so they can blame it all on the sun.

    My basic question is, it is increase in the TSI that causes the earth to warm a bit, or is it the solar maxima thing? Or both (the maxima impacting the TSI).

  11. 11
    David B. Benson says:

    Lynn Vincentnathan (10) — The minima and maxima are the changes in TSI over the solar cycle; TSI drives the climate.

    While most climatologists seem to think that the global surface temperature change from a minimum to a maximum is about 0.5–1.0 K, Tung & Cabin (2008) conclude from 50+ years of data that this change is more like 0.17 K, which is quite a bit.

  12. 12
    Richard Ordway says:

    Manu wrote, re #7 “According to the authors, it should indeed be significant.”

    Manu, How does this change the future big picture that we are in trouble unless we cut back on CO2?

    Carbon dioxide is a green house gas(Tyndall, IPCC, an experiment that high school kids do when they add CO2 to a beaker and the temp goes up and stays up for as long as CO2 in there [Classic Chemistry Demonstations -Royal Society of Chemistry).

    C02 has risen exponentially in the atmosphere and is staying in the atmosphere.(Keeling, IPCC).

    We humans are not going to stop emitting CO2 for any time in the near future.

    Result: we are committed to inevitable climate change and must take action.

    Secondly, how can the sun be causing big changes…it is not shown in other evidence and indeed is counter to physics.

    1) The upper stratosphere and upper atmosphere are currently cooling not warming or staying the same. This would be the opposite if the sun were really increasing in intensity.

    2) The fingerprint of the warming of the last thirty-fifty years does not indicate the Sun. It has been getting warmer faster at night then during the day over land and over the whole Earth not just hemispherically. (Someone please correct me if I am too strong in this line of reasoning).

    This was projected by Svante Arrehenius’s calculations for doubling the amount of CO2 in 1896 (Ambio Feb 1997)

    3) The Earth’s orbital changes (ice age cycles, volcanic action and polution aerosols have been trying to push the Earth’s surface temps to get cooler. Yet, some glaciers around the world are at 5000 or more year lows. Some ice shelves estimated at around 10,000 years old are falling into the ocean.

    If the Sun were causing these huge anomalies, it would probably have been hitting us in the nose with a sledge hammer and be obvious in ice cores and tree ring C 14 and Be ratios.

    4) According to paleoclimate evidence, the warming we are going through is perhaps unpredecedented in its speed-for at least the time of civilzation(Ecology (Vol. 89, No. 11, IPCC 2007). It should take thousands of years naturally with the Sun, etc. to do what just happened in 200 years. If it is the Sun, again, it should be so obvious as to be unmistakable.

    Now I could be wrong, but even if the Sun were stonger than formerly expected, the rate of warming we are going through is nearly unprededented and is eventually going to catch up with us unless we stop emitting Co2.

  13. 13
    Mark says:

    Lynn you don’t expect a cohesive argument, do you?

    They aren’t looking to explain anything. They’re looking to stop AGW being an explanation.

    If you’re BUILDING a theory, you need to ensure it is consistent. If you’re BREAKING one, all you need is something sharp and pointy.

  14. 14
    coby says:

    “Current climate models [Intergovernmental Panel on Climate Change, 2007] have assumed that the TSI did not vary significantly during the last 30 years and have therefore underestimated the solar contribution and overestimated the anthropogenic contribution to global warming.”

    I’m not sure the conclusion – “overestimated the anthropogenic contribution” – logically follows from models wrongly assuming “TSI did not vary significantly during the last 30 years”. It would mean something was wrong, yes, but why that necessarily?

  15. 15
    RichardC says:

    Lynn, it depends on who you ask. Scientists by and large say it is TSI that drives solar influence on climate. Since that mechanism is too small to account for climate changes, deniers say it is the solar maximum/minimum themselves, acting in a way that magnifies the TSI effect through an unknown mechanism which most likely involves GCRs.

  16. 16
    Chris Colose says:

    Lynn,

    The changes in TSI between max and min of a solar cycle have little impact on the surface temperature of the planet owing to the immense intertia of the climate system coupled with a relatively short oscillation time in TSI. The differences between PMOD and ACRIM may be important for some reasons, but not for the attributuion of climate change. To make a good argument for solar impacts on climate change, you need to look at longer term trends (which have been much smaller than the amplitude of the 11-year cycle).

  17. 17

    I posted this earlier, but it never appeared. I am interested in how IPCC arrives at the probabilities they use in their reports. Not the “virtually certain = 99%” etc., but how they arrived at the 99% (or whatever) in the first place. Where would I look to find documentation of how the probabilities are computed?

    [Response: Here. - gavin]

  18. 18
    Lawrence Brown says:

    The bottome line as far as AGW is concerned, is indicated by two quotes from Tamino’s site “Open Mind”:

    (1)”I examined two composites of satellite measurements of total solar irradiance (TSI), and showed that whether one uses the PMOD composite or the ACRIM composite, there is solid evidence that TSI has not changed sufficiently to be responsible for modern global warming.”
    And
    (2)”….whether one uses PMOD, ACRIM, or the third contender, the IRMB composite, the change in TSI is insufficient to account for modern global warming.”
    http://tamino.wordpress.com/2007/07/27/pmod-vs-acrim-part-2/

    This is in good agreement with the IPCC 2007 Fourth Assessment Report, which shows TSI contributing 0.12{0.06 to 0.30}W/m^2, while the total net anthropogenic forcing is given as 1.6{0.6 to 2.4}W/m^2.
    http://ipcc-wg1.ucar.edu/wg1/wg1-report.html

  19. 19
    robert davies says:

    Re: #5…

    I recently attended a talk by Scaffeta. If I’m not mistaken, accepting the level of TSI-induced warming he calculates w/ the ACRIM dataset — about 70% of the past century’s warming — also requires accepting his forcing calculation, based on his “complexity” argument.

    I put the question to him directly: What’s the mechanism? He shrugged his shoulders and said “complexity.” By this, he meant, I assume, feedbacks.

    Then there’s also the issue of the stratospheric cooling fingerprint, which got another shrug.

  20. 20

    Mark (different Mark? Not Mark from the UK?) wrote in 4:

    If two papers come to different conclusions then each should find out what is wrong in the other.

    After that, pass these comments back. See what changes come up. If they still disagree and point different directions, then there is no conclusion.

    Neither are right. The long term trend is officially a known unknown.

    Not so fast…

    You might want to put Scafetta in the search box above. He has a bit of a track record. Besides, the above essay points to some weak links in the Scafetta and Willson paper. Doesn’t mean that its wrong, but the evidence and justification lean one way, not the other, and while certainty is impossible, arriving at justifiable albeit tentative conclusions is often necessary. In reality, independent of what anyone knows, chances are one conclusion is true and the other is false, at least at an appropriate level of accuracy.
    *
    Mark (he is the one) wrote in 13:

    They aren’t looking to explain anything. They’re looking to stop AGW being an explanation.

    If you’re BUILDING a theory, you need to ensure it is consistent. If you’re BREAKING one, all you need is something sharp and pointy.

    Bingo.

  21. 21
    Jim Norvell says:

    There are a couple of papers out recently by Willis, J.K and Loehle, Craig (separately) that indicate that there has been no net heating of the upper 700 meters of the ocean since about 2003. If it is true that we have a net forcing of something like 1 w/m^2, where is the energy going?carctting

  22. 22
    Mark says:

    Timothy, read the earlier bit.

    There will be issues with both papers.

    Address them.

    If there’s still no agreement when those issues are addressed, the answer is officially a known unknown.

  23. 23
    CM says:

    Jim (#21), which paper by Willis exactly? Anyway, have a look at a longer time series, e. g. the three studies of ocean heat content for 1955-2008 superimposed in the graph on p. 13 of Levitus et al. 2009. You may want to reconsider the importance of any 5- or 6-year “trend” for the 2003-2008 period, taking into account the amplitude and duration of the wobbles about 1980-85 and 1988-1995 or thereabouts, and the fact that the long-term trend has clearly been up.

  24. 24
    pete best says:

    Re #22, Is that your interpretation of the scientific method. I have read articles of many a scientists how set out to disprove something they did not agree with but ended up reinforcing it. When something becomes reinforced for a century there is more truth to it than mere falsification can find.

  25. 25
    Mark says:

    re 21.

    Dunno, but have you asked the sea below 700m?

  26. 26
    John Cross says:

    Excellent post. Especially appreciated since I am very busy at work these days and don’t have the time to track these things myself. One very minor typo. In paragraph 4 you refer to SW08 instead of SW09.

    Best,
    John

  27. 27

    Gavin, I have a question I have wanted to ask for quite a while, and now that ocean heat content has come up, I’m hoping this is an opportunity.

    Isn’t the 0.85 W/m^2 used in your paper Hansen et al 2005 much too high to match up with all the empirical work on ocean heat content?

    The recent work by Domingues et al, or Levitus et al, suggest that the upper heat content of the ocean is increasing by 0.4 *10^22 J/year, and that works out to about 0.25 W/m^2. (The conversion factor of 1.6e22 is given in S1 of Hansen et al 2005).

    The heat into deeper parts of the ocean is universally agreed by modelers and measurements to be substantially less than what goes in to the top 700m, as far as I can see.

    Hansen et al 2005 cites Levitus et al 2000 with approval – but in fact they give a warming rate of 0.3 W/m^2. In the text of Hansen et al 2005 this is research is described as “Levitus et al. (15) compiled ocean temperature data that yielded increased ocean heat content of about 10 W year/m2, averaged over the Earth’s surface”
    That’s about 0.25 also, given a 40 year period being considered.

    Hansen et al 2005 then cited Levitus et al 2004, as follows:
    […] yields a global mean heat storage rate of 0.7 x 0.86 = 0.60 +/- 0.10 W/m^2 per year or 6 +/- 1 W year/m^2 for 10 years, 0.7 being the ocean fraction of Earth’s surface. This agrees well with the 5.5 W year/m^2 in the analysis of Levitus et al. (21) for the upper 700 m that was based only on in situ data.

    But it doesn’t agree at all! THAT reference estimates 0.2 W/m^2 over the Earth’s surface.

    The units here are awkward. 5.5 W year/m^2 is not a unit used in Levitus et al, but if this is over the earth’s surface, then it corresponds to a total heat increase of about 9e22 J. Levitus et al give 14.5e22 J – but that is over more than 40 years, and so the global mean heat storage rate is again something like a third to a quarter of your value.

    The analysis by Levitus et al has been improved since, and there’s the Domingues (2008) analysis as well – which you’ve blogged at Ocean Heat Content Revisions last year. But the over all trend remains steadfastly much less than Hansen et al 2005, all the time.

    I don’t get it. The paper Hansen et al seems to be citing material which consistently suggests values around a third of less of the 0.85 given with the models, but never seems to recognize this disparity. (There seems to be some recognition of a problem when you discuss eustatic sea level measures.) I use your stuff a lot, but this one has bothered me enormously. I’d really appreciate some comment.

    Do you guys still stick by 0.85 W/m^2 imbalance (+/- 0.15)? Am I misreading all the other work on sea levels and ocean heat and so on as giving a third of this or less?

    [Response: The 0.85W/m2 was the instantaneous ensemble mean value in simulations for 2005, not the the long term average (which is smaller). The models suggest that the imbalance (on average) should be growing with time, so any comparison for the long term needs to look directly at the appropriate diagnostics - as was reported in Domingues et al (2008). In the real world, the internal variability may be larger than was seen in that model (GISS-ER), but recent trends are somewhat uncertain as well (compare Levitus, Ishii and Domingues), so it seems likely that more time will be needed to have a fair assessment. We'll see. - gavin]

  28. 28

    The link Gavin gave in response to my comment (no. 17) didn’t work. Here are two links that address the subject of uncertainties:
    http://www.ipcc.ch/pdf/supporting-material/ipcc-workshop-2004-may.pdf
    http://www.ipcc.ch/pdf/supporting-material/uncertainty-guidance-note.pdf

  29. 29
    Mark says:

    re 24.

    It is ONE METHOD of ensuring scientific rigour.

    If two people say that the sun is changing and one says “hotter” and one “cooler”, then you ask for proof.

    When they have produced proof, you can check the proof for rigour. This should not be the person who wrote it.

    When queries about the rigour are brought forward to the writer of the piece, they can change their proof to include that change, redo the experiment to counter the proof or find that they were incorrect and withdraw their statement.

    This is what happened with the Hockey Stick.

    [edit]

    As it was, the conclusion was reinforced.

    PLEASE!!!! Ignore that people still regurgitate “the Hockey Stick is a fake” since there are people unconcerned with truth and idiots will regurgitate whatever they’ve been told is true, whether it is any more or not. Their ignorance of the result of the original concerns being that the conclusions were robust doesn’t mean that the actions described never happened.

  30. 30
    Joel Shore says:

    Re #27: In addition to what Gavin said, it appears from this recent talk by Hansen: http://www.columbia.edu/~jeh1/2009/Copenhagen_20090311.pdf that he now thinks the ocean heat content data are compatible with a somewhat lower estimate of the radiative imbalance of 0.5 +- 0.25 W/m^2 (see charts #14 and 29 in that talk).

    To the extent that this differs from what the models predict (he quotes that as 0.75 +- 0.25 W/m^2, so there is some difference but not really outside the current errorbars on each), he seems to think that this may be due to the models tending to overestimate the climate time constant stemming from ocean mixing (see his AGU lecture here: http://www.columbia.edu/~jeh1/2008/AGUBjerknes_20081217.pdf) and that it may mean that the current radiative forcing is on the lower end of estimates because the magnitude of the negative aerosol forcing is on the high end (i.e., more negative) end of estimates.

    Of course, one could argue that it might also suggest that the climate sensitivity is toward the lower end of the estimates (again, with the caveat above that I made about errorbars). However, Hansen seems quite confident that the estimate of climate sensitivity from the ice age – interglacial cycles is quite precise, which is partly why he believes that the issue is with the time constant. (I think he has some other reasons to be suspicious of the time constant as noted in that lecture.)

    So, that at least is my reading of Hansen’s own current views on the subject, on the basis of those two recent lectures of his.

  31. 31
    Mark says:

    Why the edit to #29 Gavin? There were valid problems with the graph. One was “it’s not long enough to be statistically significant”. Which was, as I recall, true. Zero effect was within the error bars at 99% confidence.

    In that instance, wait for more data and that extra data reduces the error and allowed the effect to become stronger. And it proved the graph right.

    The two things I aimed for was

    a) Saying “you got this wrong” and being RIGHT about it is skepticism.
    b) When what you say was wrong is fixed, stop saying it is wrong.

  32. 32
    Mark says:

    And further to 31, those two things are how science advances.

  33. 33
    Hank Roberts says:

    > as I recall
    Citation needed, of course. That’s how science … but you know that.
    It’s a blog. But we can try hard to give sources beyond recollection.

  34. 34
    Ricky says:

    I noticed that SW09 uses Krivova et al. to bridge the ACRIM gap and come to the conclusion of a ’96 higher solar minimum. Ironically LF08 quote the same Krivova in support of the PMOD composite; indeed, the Krivova proxy shows no increase in ’96 solar minimum.

    Should I deduce that Krivova’s model works for solar maxima but not for minima? ;)

  35. 35
    Mark says:

    Hank, what google phrase do you suggest? The noise on Google when you make ANY search on “Global Warming” and ESPECIALLY “Hockey Stick” will get you ten thousand links to tripe written by bloggers.

    Here we have access if not to those directly involved, those who are in reasonable contact with those who were.

  36. 36
    Alf Jones says:

    Slightly off topic, but does anyone have any comments about the numbers used by David Whitehouse in the british Independent for the warming effect from a solar cycle compared to carbon dioxide?
    http://www.independent.co.uk/news/science/the-missing-sunspots-is-this-the-big-chill-1674630.html
    “…1.3 Watts of energy per square metre at the Earth. This means that during the solar cycle’s rising phase from solar minima to maxima, the Sun’s increasing brightness has the same climate-forcing effect as that from increasing atmospheric greenhouse gasses.”

    Is this right? Could this mean that a downturn in the solar activty could help to hold back GW?

    Alf

  37. 37
    tamino says:

    Re: #36 (Alf Jones)

    The 1.3 W/m^2 change in solar insolation is only for an object with all its surface area directly facing the sun. Since the area of the earth is one fourth its cross-sectional area, the top-of-atmosphere radiation change due to a 1.3 W/m^2 change in solar insolation is only 1.3/4 = 0.325 W/m^2.

    And 30% of that extra insolation is reflected right back to space (earth’s albedo), so the *climate forcing* is actually a mere 0.7 * 1.3 / 4 = 0.2275 W/m^2.

    That’s nowhere near the climate forcing due to increasing greenhouse gases. If David Whitehouse has the gumption to write a book about the subject, HE SHOULD KNOW THIS. So his statement isn’t just a mistake, it’s either astounding ignorance or outright dishonesty.

  38. 38
    Martin Vermeer says:

    Re #36 Alf Jones:

    eh, those 1.3 watts per square metre are referred to a square perpendicular to the direction to the Sun at the Earth’s orbit. The similar amount, also expressed in watts per square metre, of CO2 (or total, including aerosols) radiative forcing, is referred to a square at the Earth’s surface. There are four squares of the second kind for every square of the first kind… so that’s an error of 75% :-)

    It gets worse. Before that TSI variation of 1.3 W/m2 reaches the ground, 30% is bounced straight back into space, leaving only 70% of 25% = 17.5%, an error of 5.7 times…

    This mistake seems to be popular with the more clueless segment of denialism. There are some amusing but exasperating exchanges on the Internet where brave souls are trying to educate the uneducable…

    In short, does the downturn in solar activity help to hold back GW? No, not a lot.

  39. 39
    tamino says:

    Correction: the cross-sectional area of a sphere (the earth) is one fourth its surface area. The rest of the numbers are correct.

  40. 40
    Martin Vermeer says:

    Tamino and I really didn’t co-ordinate our answers, really not ;-)

    (If we had, I would have taken the opportunity to point out that four times / one quarter mix-up)

    BTW this puts paid to Theo Hopkins’s notion in another thread that if only there were no natural variability producing a flat spell every now and then in the temperature record, the “skeptics” wouldn’t be so successful at confusing the public. Well, in your dreams. They manage even to confuse simple geometry.

    Alf Jones, would you please do something for me? Wade through all seven pages of comments to the article at the Independent, and check that nobody has brought up this geometry issue (I expect nobody has). Then, post a comment of your own linking back to this discussion, pointing out that Dr Whitehouse, far from being brilliant, is an [edit]. (Use your imagination, and your legal counsel’s advice, on the last :-) )

  41. 41
    Alf Jones says:

    re #37 & 38 (Tamino and Martin)
    Thanks for the comments. David Whitehouse used to be a science correspondent for the BBC. It seems rather sad that instead of reporting the science he is now trying to re-invent it. I will take more care with any of the claims he makes in the future.

    Alf

  42. 42

    Alf,

    The 1.3 watts per square meter figure sounds bogus. Where did it come from?

    TSI varied from about 1363 to 1368 watts per square meter over the past 400 years according to Lean’s TSI reconstruction, which is the most volatile of all the ones out there. Let’s explore what that means. Say it was a steady increase over the last 50 years (not true, but let’s say it was). TSI went up 5 watts per square meter.

    Flux density absorbed by the climate system is:

    F = (S / 4) (1 – A)

    where S is the solar constant (TSI), A the Earth’s bolometric Bond albedo. The factor of 1/4 comes about because the Earth is a sphere but receives solar energy on its cross-sectional area (pi R^2 instead of 4 pi R^2). A for Earth is 0.306 according to NASA. F would then increase, given TSI moving from 1363 to 1368, from 236.48 W/m^2 to 237.35 W/m^2, an increase of 0.87 W/m^2. Where does the 1.3 W/m^2 come from?

    CAPTCHA: resumes joggling

  43. 43
    Hank Roberts says:

    Mark, you asked for a suggested Google search:
    http://www.google.com/search?q=“Hockey+stick”+hand+drawn+IPCC
    The first result is:
    http://scienceblogs.com/stoat/2007/05/tggws_again_again.php
    I’m not sure exactly what you were talking about above — if you had a cite to which of the many charts you might have meant, that got edited out — but if you were talking about the original in the IPCC, Stoat covers it there.

  44. 44
    Benjamin G says:

    The IPCC chapter on detection and attribution of climate change (working group one) mentions the solar cycle and says that studies indicate a .1 deg C oscillation in the temperature record attributable to the 11 year solar cycle. This is one reason why they say that several decades of data is needed for detection and attribution studies.

    I don’t have a link, but I’ve read Hansen saying that the change in solar input over the 11 year cycle would cause a temperature change of .2 deg C if it’s duration were longer and rise/fall of the new cycle didn’t head off further temperature change in a given direction.

    The fall off from peak to minimum only takes about 5-6 years. We are a year and a half into the longest and deepest solar minimum in a century.

    I think it’s no stretch to say that we’ve seen a change in solar forcing over the last 6 years that will, if a new solar cycle doesn’t kick in, lead to a negative forcing on the order of -.2 deg C.

    That compares favorably with the .2 deg C/decade forcing that the IPCC predicts for our GHG emissions, coming as it does in a shorter time period.

    My assesment: the pronounced and extended dip in the solar forcing we’ve seen since about Jan ’03 can indeed explain some of the recent dip in temperatures.

    It seems obvious to me, just from what I’ve read in the IPCC about the size of the oscillation in the temperature record. Don’t ask me to do any calculations relating it to TSI. :)

  45. 45
    Mark says:

    Hank, #42, that link gave nothing. Just two short paragraphs.

    And, as rather expected, that google search string pulled up a lot of denialist sites and no original discourse, that likely having been bumped WELL down the list by more modern linkings.

    My statement that finding the original details is not possible using google since all the links are tertiary at best and overrun by denialists at worst.

    Do you want to try again?

    NOTE: I remember that the error in the graph for the original Hockey Stick meant that the warming trend could be X +/- 1.2X, whatever X was. Therefore it was *BARELY* possible that the change could be zero.

    The data was collected more and the X became higher and the error smaller until zero no longer was in the 3 SD limit of statistical significance.

  46. 46

    No need to post this but there’s a typo in your update: \in temrs of\ should be \in terms of\.

    [Response: Thanks! Fixed. -rasmus]

  47. 47

    Those who want the low in the solar cycle to reverse global warming need to explain why temperatures the last couple of years (with the help, remember, of a big La Niña) are still at relative highs vs. before 1998. NASA’s GISS land-ocean data set has 2008 as warmer than anything before 1998. Likewise for HadCRUT3: it has 2008 as warmer than any year since 1997. The combined effect of La Niña and a low in the solar cycle has only masked the underlying warming trend slightly, not pulled it back.

    Look at HadCRUT3 in the 19th century to get a sense of how much natural variation there is in the system. The little jiggles we’ve seen the last 10 years are small compared with past inter-annual variations.

  48. 48
    Jim Cross says:

    #46

    I am NOT a believer in “it’s all the sun” theory, but I do believe that solar influence has been underestimated.

    The explanation for what you ask is simply lag in the climate systems. Solar cycle 23, remember, was relatively intense and only ended a year or two ago. Sun spot counts were high but diminishing through 2007. The near zero sun spot count is only a phenomena of the last year or so.

  49. 49

    Re #44 & 47–

    The 2008 GISS summary does (somewhat tentatively) attribute the slightly cooler temps of 2008 to, in part, the slightly lower insolation of this very quiet and prolonged solar minimum.

    Of course, some are trying to use this to obfuscate with the unwarranted implication that, if the sun’s doing then CO2 isn’t. Others seem quite oblivious to the point that the solar minimum is cyclical, or unreasonably convinced that it will be a new Maunder Minimum.

    Hansen’s summary (if I understood it correctly) stated that the current reduction in insolation modified the net forcing in an amount equivalent to about seven years of GHG emissions at 2008 rates, which I think puts the matter in perspective. My conclusion is that, if we’re lucky, we may have a couple of more years to act effectively to mitigate emissions. If we’re unlucky–which really means unwise–we’ll take it as an excuse to twiddle our thumbs that much longer.

  50. 50
    Julius St Swithin says:

    It may not be significant but the correlation between both sunspots and 10.7 cm radio flux and, for that matter, inverted cosic ray counts, appear to be better than for ACRIM solar insolation values.

    See http://www.climatedata.info/Forcing/forcing.html and click on sunspots


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