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What if the Sun went into a new Grand Minimum?

Filed under: — group @ 19 June 2011

Guest commentary by Georg Feulner

During a meeting of the Solar Physics Division of the American Astronomical Society, solar physicists have just announced a prediction that the Sun might enter an extended period of low activity (a ‘grand minimum’) similar to the Maunder Minimum in the 17th century. In this post I will explore the background of this announcement and discuss implications for Earth’s climate.

It has been known for a long time that solar activity shows a very regular pattern. Every 11 years the Sun is particularly active, and numerous dark sunspots are visible on its surface. These maxima of solar activity are separated by times of low activity when only few (if any) sunspots appear.



Figure 1: The Sun in visible light during an activity maximum (left) and during the last (and rather extraordinary) 11-year minimum during which it appeared spotless most of the time. Source: NASA Earth Observatory/SOHO.

One could think that the Sun emits less light during a solar maximum because of the many dark spots. In fact it is the other way round, since active regions around the sunspots emit more radiation than is “lost” in the cooler sunspot areas. This effect can be best seen in ultraviolet images of the Sun.



Figure 2: The Sun in ultraviolet light during a maximum (left) and a minimum (right). Source: NASA Earth Observatory/SOHO.

An analysis of historic sunspot observations shows that the 11-year solar activity cycle was interrupted during the late 17th century.
This period of time, during which the Sun appeared without sunspots most of the time, was called the Maunder Minimum by Jack Eddy in his famous Science paper. (Alliteratively named after Edward Maunder, although it was actually first discovered by Gustav Spörer.)



Figure 3: Observations of the number of sunspots over the last four centuries. Source: Wikimedia Commons/Global Warming Art.

The Maunder Minimum falls within the climatically cooler period of the “Little Ice Age”, during which temperatures were particularly low over continents in the Northern hemisphere (especially in winter). It has long been suspected that the low solar activity during the Maunder Minimum was one of the causes of the Little Ice Age, although other factors like a small drop in greenhouse gas concentrations around 1600 and strong volcanic eruptions during that time likely played a role as well.

Solar physicists do not yet understand how an extended solar-activity low like the Maunder Minimum arises. Yet there is recent observational evidence for an unusual behavior of the Sun during the current cycle 24, including a missing zonal wind flow within the Sun, decreasing magnetic field strength of sunspots and lower activity around the poles of the Sun. These observations prompted Frank Hill and colleagues to suggest that the Sun might enter a new Maunder-like minimum after the current 11-year cycle ends (i.e. after 2020 or so).

It remains to be seen whether this prognosis turns out to be true (there have been some doubts expressed), but since grand minima of solar activity did occur in the past, it is certainly interesting to explore what effects such a minimum might have on 21st century climate if it did occur. This is precisely the question Stefan Rahmstorf and I investigated in a study published last year (see also our press release. (Earlier estimates for the size of this effect can be found here and here.) In our study we find that a new Maunder Minimum would lead to a cooling of 0.3°C in the year 2100 at most – relative to an expected anthropogenic warming of around 4°C. (The amount of warming in the 21st century depends on assumptions about future emissions, of course).



Figure 4: Rise of global temperature (relative to 1961-1990) until the year 2100 for two different emission scenarios (A1B, red, and A2, magenta). The dashed lines show the slightly reduced warming in case a Maunder-like solar minimum should occur during the 21st century. Source: PIK.

According to these results, a 21st-century Maunder Minimum would only slightly diminish future warming. Moreover, it would be only a temporary effect since all known grand solar minima have only lasted for a few decades. Critics of this result might argue that the solar forcing in these experiments is only based on the estimated change in total irradiance, which might be an underestimate, or that does not include potential indirect amplifying effects (via an ozone response to UV changes, or galactic cosmic rays affecting clouds). However, our model reproduces the historic Maunder minimum with these estimates of solar irradiance. Furthermore, even if one multiplied the solar effects by a huge factor of 5 (which is unrealistic), no absolute cooling would take place (the temperatures would be temporarily cooler than the base scenario, but the trends would still be warming).

It is clear that if a grand minimum were to happen it would be a tremendously exciting opportunity for solar physicists, however it is unlikely to be very exciting for anyone else.

Update 23 June: Here is a nice tongue-in-cheek video on the media response to this story.


65 Responses to “What if the Sun went into a new Grand Minimum?”

  1. 1
    Chris Colose says:

    With all due respect, the main conclusions of the Feulner and Rahmstorf study seem not only self-evident, but something that can be worked out on the back of an envelope, at least to a good first approximation (especially when placing it in the context of a warming signal an order of magnitude greater by end century). For example, the Total Solar Irradiance around solar minimum is ~1360 W/m2 (Kopp and Lean, 2011), and estimates of the solar decline toward Maunder Minimum are of order ~0.1%, so the associated radiative forcing is 1360*0.001*(0.7/4) ~ 0.24 W/m2, which even at equilibrium is about 0.2 degrees C for a reasonable climate sensitivity. There’s no way to make that competitive with CO2 by end century even with [probably] unreasonable amplification factors.

    Another interesting question concerning a new Maunder Minimum would be the impacts on decadal-scale prediction, where both internal variability and changes in TSI are competitive with changing greenhouse gases.

    [Response: I agree with Chris that the simplest back-of-envelope argument is fully sufficient to make the point. It does seem though, that these days it is necessary to publish the obvious in repeatedly different and more catchy forms in order to get the word out. To get attention, a new paper, and new press release, is necessary, and besides that it appears that a lot of things that are well-known to everybody in climate science haven't been articulated in a conveniently citable form (though one can find estimates like Chris's embedded in various discussions of solar variability). The thing I find a bit curious about the result that is the subject of this blog article, though, is the statement that the model used reproduces the Little Ice Age climate simply as a response to the luminosity reduction. That is at odds with what one finds in GCM's, and is in fact what prompted the search (e.g. in Shindell's paper) for fancy amplifying mechanisms based on UV variability, ozone feedback and strat/trop coupling. So, the small reduction in warming in 2100 is fully expected and compatible with standard climate sensitivity arguments, but the statement that the same physics accounts for the Maunder Minimum response is not. I suppose it may have something to do with what one considers the LIA signal to actually be. It's fairly small in the global mean, but as a regional climate signal much bigger and hard to account for by insolation reduction, when put into full GCM's. Comments from the authors? --raypierre]

    [Response: Ray, we're discussing the global mean temperature response. The fact that a wide range of different models (including ours) give a reasonably good simulation of the past millennium with this forcing was already shown in the IPCC AR4, see Figs. 6.13 and 6.14. -stefan]

    [Response: Right, but does this really mean there's nothing left to explain about the LIA? Can you actually get the magnitude of the Northern Hemisphere regional response right just as a response to reduced luminosity? Again, the whole reason so many researchers are looking for more exotic mechanisms for the LIA is that it is hard to account for the magnitude of NH (especially European) expression of the LIA when forcing with just the straight luminosity reduction. I am willing to believe, however, that maybe some of what we call the LIA is within natural variability, and that the regional signal that needs to be explained is not as large as some think. --raypierre]

  2. 2
    Edward Greisch says:

    “What’s Down with the Sun? Major Drop in Solar Activity Predicted”

    Do you have a good model for what goes on in the interior of the sun? Since 21st century instruments were not available in 1650, it seems to me that you need a good theory of the sun’s interior to make such a prediction. Relying on what can be seen on the solar surface and corona seems like weather forecasting.

    Thanks for the File:Sunspot Numbers.png graph and the 1000 year sunspot graph. I notice that the 1950s were a time of peak oscillations and also good economic times.

  3. 3
    Edouard says:

    Unfortunately, direct observations of the Sun just before the Maunder Minimum were not frequent and precise enough to understand how the Sun entered into this prolonged minimum (in particular how the 11-yr sunspot cycle collapsed). Cosmogenic nuclides should teach us part of this story, but we still need a larger and more precise database in order to test if the present behavior of the Sun is indeed a good analog for the start of a Grand Minimum.

    Actually, the discovery of the Maunder Minimum should be attributed to the French astronomer Jean-Jacques Dortous de Mairan (1678-1771), who reported a link between solar activity, based on the abundance of sunspots, and the frequency of aurorae observed at mid-latitudes (e.g. in Paris or Montpellier). He described the concomitant decrease of both phenomena around 1645 and their subsequent increase around at the beginning of the 18th century during which he was living. This seventy year period of anomalous solar behavior was studied again more than a century later by Edward Maunder, whose name would ultimately be associated with this period by Jack Eddy.

    J.J.D. de Mairan, Traité Physique et Historique de l’Aurore Boréale, Imprimerie Royale, Paris, 1754, pp. 1–570, 1st édition 1733, 2nd edition.

  4. 4
    R. Gates says:

    Interesting analysis. Politically, global warming will be a hard sell during the early years of a Maunder type minimum as temperatures take a several year rapid plunge (around 2020 on your chart). During that time, the idea of restricting the burning of fossil fuels could well lose its luster. In such an eventuality, we might find that CO2 levels are actually higher by 2100 than they would have been without a quiet sun period earlier in the century.

    [Response: Those sharp dips are from volcanic eruptions that were put in to make the scenarios more realistic (though of course no-one knows when the next big climate-affecting eruption will be). We should have made that clearer though. - gavin]

  5. 5
    Septic Matthew says:

    It is clear that if a grand minimum were to happen it would be a tremendously exciting opportunity for solar physicists, however it is unlikely to be very exciting for anyone else.

    I think that you underestimate how much interest there will be in comparing the measured temperature to the modeled temperature.

    [Response: Not at all. That is is always interesting (if done properly of course). But the 'excitement' generated by this story outside the solar physicist community seems almost entirely confined to the fringe who are predicting a new ice age. They will be sorely disappointed. - gavin]

  6. 6
    vukcevic says:

    Minimum of 1810 type is on cards, couple of low cycles, but nothing approaching the Maunder type minimum.
    http://www.vukcevic.talktalk.net/NFC7.htm
    http://www.vukcevic.talktalk.net/LFC2.htm
    There is no reasonable correlation between the longest temperature record (CET) and the sunspot activity.
    http://www.vukcevic.talktalk.net/CET-SSN.htm

  7. 7
    vukcevic says:

    Observations by Matthew Penn and William Livingston (refered to in Frank Hill and colleagues link, see above) is an interesting discovery, but conclusions drawn from it are by no way definitive. The effect may be associated with a deeper and longer minimum (as the current one is) but it appears that the effect may reversible; there some indication to that as shown here:
    http://www.vukcevic.talktalk.net/L&P.htm
    Next year or two may show true trend of this effect.

  8. 8
    Timothy says:

    For those curious about the pronounced dips in the future scenarios here they are responses to Pinatubo-scale volcanic eruptions that are assumed to occur at a reasonable frequency over the course of the next century.

    I have to say that I was wondering whether anyone had done any such climate simulations when I heard the news, so thanks very much for the post. I think people would be a bit more interested in the difference over a decadal time-frame. You conclude that a 0.3K difference is the maximum you would expect by year 2100, but this is equivalent to about one decade of global warming at present rates [0.3K/decade?], so presumably this could create a one-decade pause in global warming were such a minimum to occur now.

    Of course, on a timescale of one decade the noise in the temperature signal from internal variability and measurement uncertainty is quite large, so this might be hard to determine, though tamino showed that five year means show a monotonic increase over recent decades, and one might not unreasonably expect this to cease for a decade in a grand solar minimum scenario.

    I’d be very interested to see the difference in a well-initialised decadal forecast between the two possibilities [grand solar minimum/solar business as usual].

  9. 9
    Timothy says:

    [R Gates] – “Politically, global warming will be a hard sell during the early years of a Maunder type minimum as temperatures take a several year rapid plunge (around 2020 on your chart)”

    See my post at 7 – this plunge is due to a volcanic eruption they’ve included in their scenario. Note that it is present in all the runs, not just those with a grand solar minimum. This confused me at first too, but Fig. 2 of the paper explains everything.

    As far as I was aware most climate model scenarios include a constant, small, forcing for volcanoes, rather than arbitrary, episodic forcing. It doesn’t make much difference to the 2100 temperatures, but it can make differences in the timeseries confusing.

  10. 10
    Robert Reiland says:

    Even if there were a significant negative effect on the increasing temperature trend due to a cooler sun, we would still have the problem of “ocean acidification” from carbon dioxide added to the atmosphere. In fact the cooler the oceans are, the more rapidly carbon dioxide would dissolve into the water. Given the slow rate of temperature changes for large bodies of water and the tiny hypothetical effect of a cooler sun, I doubt that rates of ocean acidification would be affected much, but there would be some effect.

    It’s important to remember that greenhouse gases, particularly carbon dioxide, affect the biosphere in multiple ways. Looking at temperature trends alone misses much that is important. No matter what other factors affect temperature, the addition of large amounts of carbon dioxide to the atmosphere-ocean system will produce large negative effects.

  11. 11
    meteor says:

    two things:

    1-what about your graph?

    The A1B scenario warming, in 2100, is not 3.8°C but 2.8°C (see IPCC 2007)
    On your graph the cooling is only 0.1°C not 0.30°C as in the text.
    So there is an evident minoration of the “Maunder effect”

    2 this sentence:

    “It is clear that if a grand minimum were to happen it would be a tremendously exciting opportunity for solar physicists, however it is unlikely to be very exciting for anyone else”

    is, at least, understandable.

    A solar grand minimum should be exciting for climate scientists who are interested, by example, by the local effect (for winters in Europe and in the US)and many other effects in the stratosphere.

  12. 12
    meteor says:

    sorry, in my precedent post we must read “incomprehensible” not “understandable”

  13. 13
    JCH says:

    You include volcanic activity in the climate models. It appears you did not include a solar minimum. Why not?

    As for climate scientists being out of work in a solar minimum, me, I’m hiring people who understand how to warm up this joint.

  14. 14
    Dan H. says:

    This idea has been put forth previously, although compared to a Dalton-type minimum and not a Maunder-type.

    http://sesfoundation.org/dalton_minimum.pdf

  15. 15
    Will Hansen says:

    It is worth noting that Theodor Landscheidt – one of iconoclasts in the ‘solar-forcing-trumps GHG’s’ school of European solar physicists – predicted this possible Grand Minimum based on the theory that Gliessberg cycles generated by the Sun’s oscillation around it’s centre of mass directly affect the Coriolis force perturbing solar plasma flow and the solar dynamo.
    He took to self-publishing through his own independent research institution rather than academia and peer review for this paper:

    http://www.schulphysik.de/klima/landscheidt/iceage.htm

    But on re reading it in my files he really does seem to have made a valid prediction and call on intensities of cycle 23 through and beyond 25 and the implications re a Grand Minimum.
    Indeed there had been a suggestion that should this hiatus in sun spots prevail it should be called the
    Landscheidt Minimum.

  16. 16
    Jim Eager says:

    JCH “It appears you did not include a solar minimum. Why not?”

    Why? Was there a solar minimum in C20?
    In 2010 was one predicted anywhere outside of the denialsphere?

    Why wasn’t an major asteroid-strike include as well?

  17. 17
    vukcevic says:

    Will Hansen
    Theodor Landscheidt is a rather vague in comparison to the precision of the ‘Vukcevic formulae’
    http://www.vukcevic.talktalk.net/NFC7.htm
    http://www.vukcevic.talktalk.net/LFC2.htm

  18. 18

    @grnhse_gas_bros says:
    shoutout to folks at RealClimate for clearly pointing out that SUN IS NOT STAR of show

  19. 19
    David Beach says:

    Of greater interest to me is the reduction of UV in a sunspot minimum. This must affect the upper atmosphere, so would there be an induced affect on the lower atmosphere?

  20. 20
    H. Beijeman says:

    Figure 4 only shows the warming up to 2100, a mind boggling 4C in a century. Just what do the models predict for a much longer period? dT = 40C @ T=2300 ? By how much can the temperature really rise (theoretically)?

  21. 21
    DeNihilist says:

    Dr. Schmidt,

    if I remember right, was it not you who suggested that with the dampening of the sunspots, TSI may even rise?

    Well it seems the Dr.Svalgaard thinks somewhat along the same lines. If I may –

    (Leif Svalgaard says:
    June 16, 2011 at 1:44 pm
    (Mark Wilson says:
    June 16, 2011 at 1:03 pm
    Of course nobody knows if the TSI during a grand minimum is equivalent to TSI at the bottom of normal cycle, or if it is lower.)

    If we assume that the L&P effect is that magnetic field does not concentrate into dark visible spots, variations of TSI which is normally composed of a darkening due to spots plus emission from the surrounding magnetic field areas [twice as much as the darkening] might miss the darkening effect [when there are no spots], so TSI during a Grand Minimum might be higher than TSI now.}

    I think that the ability to really test some hypothesis about a minimum is going to be very exciting!

    [Response: Not me. We talked about the temperatures going down potentially with higher sunspots based on the (possibly very dubious) spectral results reported in Haigh et al (2010) - but I think that is unlikely. Leif's point is interesting - but in itself not very convincing. Having a grand minimum happen would obviously clear things up considerably. - gavin]

  22. 22
    Chris Colose says:

    David Beach (#19)

    A great review on the various solar impacts on climate is by Gray et al (2010) available here [PDF]. Note that the UV variations are strongly disproportionate to the integrated TSI change, and can reach up to 100% variation (depending on the wavelength interval), ~6% at UV wavelengths in the stratosphere, and temperature anomalies of ~1000 K in the very uppermost regions of the atmosphere; section 4 of the Gray et al. paper discussed UV changes and stratospheric feedbacks.

    Another interesting question, on a larger planetary evolution scale, is the role of the very short wavelengths in eroding planetary atmospheres. The shortwave extreme ultraviolet flux is much higher in the distant past, which could pose problems for early Mars to develop a very dense CO2 atmosphere early on for example, since C and O could escape from Mars early in its history (driven by these energetic wavelengths).

  23. 23
    AIC says:

    Re 15:

    Perhaps “Landscheidt Lessening” ?

  24. 24
    Magnus W says:

    So if this could be regarded as a good reconstruction (only the NH tropics I know) how much would it affect the possible contribution from the sun?

    http://journals.ametsoc.org/doi/abs/10.1175/2011JCLI4145.1

  25. 25
    Timothy says:

    “You include volcanic activity in the climate models. It appears you did not include a solar minimum. Why not?”

    They did include a solar minimum, not only that they included one that lasts throughout most of the 21st century – far longer than the period of time that the Maunder minimum persisted.

  26. 26
    stuart says:

    There is some research that links solar minimums to increased volcanic activity, which would have a much greater effect on climate temperatures than just solar activity.

    [Response: What possible mechanism could cause this? Any such coincidence is almost certainly just a coincidence. - gavin]

  27. 27
  28. 28
  29. 29
    Georg Feulner says:

    @1:

    You are right, of course, but this is true for any estimate of global temperature response to known forcing. If we had done a simple back-of-the-envelope estimate, surely someone would have criticized us for not using a climate model… Besides we also looked into regional patterns and the sea-ice response in our paper, something one cannot do without a climate model.

    @3:

    Thanks for the information about de Mairan, I was not aware of his work in this context.

    @11:

    On your first comment, part of the discrepancy between our model’s warming and the IPCC result is due to different reference periods. The IPCC uses the difference between the 2090-99 and 1980-1999 averages while we use anomalies relative to 1961-1990. The corresponding value for our model is 3.5°C warming. Furthermore, the value of 2.8°C you mentioned is the best estimate from an analysis of many different models, the likely temperature rise for the A1B scenario is given as 1.7-4.4°C by the IPCC, so our result is higher than the best estimate, but well within the range of all IPCC models. In any case, the thing we are most interested in is the solar-minimum induced cooling relative to the warming trend. The cooling in the graph shown is indeed 0.1°C only as you observed, the 0.3°C arises when we, conservatively, estimate all uncertainties in the modeling and the forcings. We should have explained that better. On your second comment, I agree, a 21st-century grand solar minimum would also be interesting for climate science as well. What we wanted to say is that the effect will be small.

    @13:

    The simulations do include solar forcing, of course. The solid lines represent experiments with a repeated 11-year cycle, the dashed lines those with a new grand minimum.

  30. 30
    John Finn says:

    This blog still seems to insist on using obsolete solar activity data. I can understand the attraction. The apparent pick up in activity just after 1900 helps explain the strong warming in the early 20th century. Clearly ghg forcing cannot have been responsible. However, it’s now pretty obvious that activity has varied much less than implied by the old Lean and Hoyt/Schatten reconstructions.

    [Response: You are mistaken about what reconstructions were used. F&R used Bard et al 2000 and Wang et al (2005) (extended using 10Be reconstructions scaled to the Wang numbers at the MM). The latter reconstruction is inline with more recent work by Steinhilber et al (2009) and Viera et al (in press) (see my paper for comparisons). I agree that no-one should be using the older Lean (2000) or Hoyt/Schatten numbers any more- gavin]

    Isn’t it time to admit that you don’t actually know what caused a ~0.5 deg rise in global temperatures and a ~2 deg increase in arctic temperatures between ~1910 and ~1945.

    [Response: Odd that the only paper to make a connection between Arctic temperatures and solar activity (Soon, 2005) used the ...... Hoyt and Schatten reconstruction. Isn't that a little contradictory to your first point? - gavin]

  31. 31
    vukcevic says:

    John Finn
    The Arctic temperature regime appear to be a very specific case, any generalisation may be misplaced:
    http://www.vukcevic.talktalk.net/NFC.htm

  32. 32
    chris says:

    John Finn – If you tried a little investigation and thought you could address your own false accusation about early 20th century warming (and might not appear such a boor).

    I suspect you’re looking at the Hadcrut temperature data since that’s the one that gives “a ~0.5 deg rise in global temperatures”…”between ~1910 and ~1945″. It’s pertinent to your point that the global temperature drifted downwards a tad between 1880ish and 1910ish, a result most likely of the large volcanic activity in that period.

    So the marked early 20th century warming was likely a mixture of recovery from volcanic forcing and accumulated (but masked) greenhouse forcing [the 1880-1940 [CO2] rise from ~290 – ~309 ppm was quite significant (equivalent to nearly 0.3 oC at equilibrium with a mid-range climate sensitivity)]. With a small solar contribution, the 1910-1845 warming can be understood rather well.

    Indeed, recovery from (negative) volcanic forcing is consistent with the marked Arctic warming you mention, since the high polar latitudes are very susceptible to the cooling effects of volcanic aerosols. Recovery from this forcing probably made a large contribution to Greenland temperature rise during your period as described by Box et al (2009).

  33. 33
    One Anonymous Bloke says:

    Are solar physicists always so keen to risk having egg all over their faces? Since there is insufficient data dating from the last Grand Minimum, how can recent anomalies be seen as a sign of anything? My reading of Biesecker and Nandi’s remarks seems to support this view.
    Is it the politics of solar physics or some other forcing that is driving this phenomenon?

  34. 34
    John Finn says:

    Gavin

    Re: #30 (my post)

    Response: Odd that the only paper to make a connection between Arctic temperatures and solar activity (Soon, 2005) used the …… Hoyt and Schatten reconstruction. Isn’t that a little contradictory to your first point? – gavin]

    I’m not terribly concerned what ‘other’ papers say. How do you explain the Arctic temperature rise in the early 20th century.

    [Response: There are at least two problems in providing a robust explanation. Firstly the forcings over this period are not as well known as in more recent times (solar, aerosols, especially black carbon). Secondly, the arctic has a lot of internal variability - this implies that there is going to be a number of equally probable 'explanations' that can't really be assessed absent some additional data. So it isn't going to be either a place or a period that are going to lead to strong conclusions. - gavin]

  35. 35
    JCH says:

    They did include a solar minimum, not only that they included one that lasts throughout most of the 21st century – far longer than the period of time that the Maunder minimum persisted. – Timothy

    My question was poorly worded, but this is at which I was getting. In Hansen’s recent draft paper, he discusses recent temperature versus a solar minimum. In my understanding, which is less than rudimentary at best, the last half of the recent decade saw the global mean rebound into the teeth of a fairly prolonged spell of few spots (and a deluge of global cooling predictions.) Am I wrong about that?

  36. 36
    John Finn says:

    chris says:
    21 Jun 2011 at 2:45 PM

    John Finn – If you tried a little investigation and thought you could address your own false accusation about early 20th century warming (and might not appear such a boor).

    I suspect you’re looking at the Hadcrut temperature data since that’s the one that gives “a ~0.5 deg rise in global temperatures”…”between ~1910 and ~1945″. It’s pertinent to your point that the global temperature drifted downwards a tad between 1880ish and 1910ish, a result most likely of the large volcanic activity in that period.

    Possibly, do go on…

    So the marked early 20th century warming was likely a mixture of recovery from volcanic forcing…

    Ok – there was the Krakatoa eruption in 1883 and a major eruption in ~1902. The warming started 10 to 15 years after that. But isn’t that a bit like the last 20-30 years, i.e. El Chichon erupted in 1982 followed by Pinatubo in 1991. Perhaps the warmth of the last decade was, at least partly, due to a recovery from the Pinatubo eruption.

    and accumulated (but masked) greenhouse forcing [the 1880-1940 [CO2] rise from ~290 – ~309 ppm was quite significant (equivalent to nearly 0.3 oC at equilibrium with a mid-range climate sensitivity)].

    So the CO2 rise from 290ppm to 309ppm was responsible for 0.3 deg temp rise. Using the simple Myhre et al formula the forcing due to this rise would be 5.35xln(309/290) = 0.33 w/m2, so your 0.3 deg riseimplies a sensitivity of ~0.9 deg/w/m2. Seems a bit high but let’s run with it. How does this explain the post 1945 rise. Again using Myhre et al the CO2 forcing since 1945 can be calculated by 5.35xln(390/309) = 1.24 w/m2. Using your sensitivity figure the temperature increase should be ~1.1 deg. Just checking GISS I note that the actual temperature increase since 1945 is ~0.6 deg.

    Something doesn’t quite add up – but I knew that already (I have done a “little investigation”)

    With a small solar contribution, the 1910-1845 warming can be understood rather well.

    Can it?

  37. 37
    J. Bob says:

    John @ 36,
    take a look at my post at “comments on 2000 Years of Sea Level, #12, for some long term temperature graphs & comparisons to CO2 levels.

  38. 38
    chris says:

    O.K, good John Finn – you can address these questions yourself without boorish false accusations!

    Of course my account was a broad description of likely contributions to early 20th century warming. Note, BTW, that I stated that the greenhouse gas contribution was an equilibrium value. It’s unlikely that the greenhouse gas contribution in the period 1880-1940 was nearly 0.3 oC since that would be the full equilibrium response (under a 3 oC climate sensitivity). So your numerology re late 20th century and contemporary warming is misplaced.

    But I’m sure you know that (even if you pretend not to!). Attribution of early 20th century warming requires a more quantitative consideration of all the contributions (e.g. atmospheric aerosols, black carbon etc. as well as anthropogenic greenhouse contributions, recovery from volcanic aerosols and solar etc.). Try here for example.

    We may not know everything, but things do “add up”…

  39. 39

    #4 R. Gates

    On the contrary R. Gates, I think by 2020, much of the Arctic ice will be obviously depleted in the summer melt season, and I would say it is most likely that the majority of people will have a better idea of how greenhouse gases work. And of course by then we will likely have seen trends in the crop productivity tied to warm days and periodic events affecting crop yields. Not so hard to see the CO2 from human emissions negative impacts from that perspective.

    #26 stuart

    I think there is a possible SG/VG connection here. Like a see-saw: the Solar God relaxes while the Volcano God Expresses and vice versa. What institute did you say was doing some research in this area?

    #30, #34 John Finn

    Being not terribly concerned what other papers say means that you are not terribly concerned with utilizing the scientific method as your basis for developing your understanding. That would indicate that you prefer to believe only those papers that you like or think support your own ideas of reality. That’s not the way science works.

    #36 … John Finn

    The early part of the century is still buried in the noise a bit; sort of like weather noise is buried in climate signal. That does not mean that CO2 did not have an impact but more likely that, though having an impact, is still buried in throws of natural variation. I’m not up on recent work in the area but I’m sure they are working on coaxing out the climate signal as natural variability is becoming better understood.

    Context is key? What are you trying to imply? That uncertainty in the early part of the century reduces certainty in the latter part of the century? Or something else?

  40. 40
    carol isaac says:

    May I be practical? What will it mean for someone installing solar panels?

    [Response: Nothing. The differences are extremely small compared to average insolation and will not be visible in solar array performance. - gavin]

  41. 41
    vukcevic says:

    John P. Reisman (OSS Foundation):
    Most likely outcome is that the Arctic ice volumes could be decreasing further in forthcoming decade, while both N. Europe and N.E. US winters get much colder.
    This is not a contradiction but the consequence of negative phase of NAO.
    http://www.vukcevic.talktalk.net/NAO-.htm

  42. 42
    charles "chick" keller says:

    The study you did assumes only direct solar forcing, but I can’t help wondering if Judith Lean’s regression results (albeit linear) don’t suggest indirect forcing about equal to the direct. If so, the effect of a new extended minimum would have a larger effect. Those who argue that regressions must be non-linear may be ignoring that some of the other forcings such as ENSO might be influenced by solar activity.

  43. 43
    Gene says:

    From what I have read on this, the solar physicists who announced these findings added quite a few caveats about their studies (e.g., “If true,…”"). Clearly this is not a definitive set of results for making profound, unassailable predictions of the future. However many of their analyses appear to be based on data gleaned during the “satellite era” and thus reflect a very limited time series, especially when we compare it to the length of time that humans have walked the Earth. My understanding is that these scientists, the solar physicists, are trying to work with what they have, and three INDEPENDENT analyses of different data propose that there is a major change underway, and that we MIGHT be about to witness a new Solar Minimum. I would expect that many if not most solar physicists today would acknowledge that there are many uncertainties about what makes the Sun tick, and about the effect all those things would/might have, by both known and unknown mechanisms, on and for Earth, including our climate. The lack of comparable (i.e., modern technological) data about the Sun during and just prior to the LIA, the MWP and other important historical periods is a problem, so our understanding is, and always will be, evolutionary. I don’t intend to hang my hat on the results exclusively, but to also be mindful that other real-world observations may either support the conclusions or provide additional information that forces the theories and hypotheses to evolve in a different direction. Not being a solar physicist, I can only trust that the analyses have been done with care, following the scientific method, and accept that they could be either right or wrong with their predictions.

    That said, all I have read thus far about the climate modeling run of last year by Rahmstorf, et al., seems to suggest a heavy focus on TSI as the sole or primary mechanism for solar influence on Earth’s climate. I have read numerous reports in the past two years that relate how observations and analyses have identified as yet unclear mechanisms linking the Sun and Earth’s climate subsystems (such as the oceans). If those studies (many funded via the National Science Foundation. My question is how do we KNOW that TSI is the only component that is critical in the Earth’s climate?

    We still do not understand fully what causes clouds to form. “Because clouds are so dynamic and can contain ice, water, or a mixture of the two, they continue to be one of the hardest components of the climate system for scientists to model accurately.” (See: http://www.eurekalert.org/pub_releases/2010-12/dnnl-sb5120910.php)

    We also know that there have been periods in the past during which CO2 levels and temperatures have been comparable to what they are today, yet do not understand the mechanisms behind those warm periods with coincident high CO2. (See: http://www.eurekalert.org/pub_releases/2010-12/uoc–bsw121010.php — this particular study focuses on the Pliocene Warm Period, 3.5 to 4.5 million years ago)

  44. 44
    William says:

    That’s a huge dip about 2020 … did you factor in a supervolcno eruption to get that amount of cooling? It looks to me like a VEI 8 event would be needed to produce that dip?

    “Those sharp dips are from volcanic eruptions that were put in to make the scenarios more realistic (though of course no-one knows when the next big climate-affecting eruption will be). We should have made that clearer though. – gavin]”

  45. 45
    jyyh says:

    Made a short search on spectroscopical studies on leafs (tangentially related to the TSI question, as a notable portion of the planet is covered with plants…). The relevant question for climate change students here would be “what sort of alterations in the irradiation spectrum of the sun would produce effects on carbon fixation?”

    water is a major absorber of IR in leafs:
    http://speclab.cr.usgs.gov/national.parks/Yellowstone/ynppaper.html

    increase in UV-radiation decreases the leaf area in couple of Antarctic species (which should be quite tolerant to UV):
    http://www.plantphysiol.org/content/125/2/738.full

    normal chlorophyll complex spectrum (radiation used for photosynthesis a.k.a. carbon fixation in living plants(cyanobacteria have a slight different spectrum)) :
    http://www.life.illinois.edu/govindjee/paper/fig5.gif

    and the obligatory effect of heat-stress in the photosynthetic machinery:
    a broadleaf tolerates heat better and recovers faster than a conifer but both start showing a decrease in photosynthesis if T>40C:
    http://connection.ebscohost.com/c/articles/8052611/temperature-induced-changes-photosystem-ii-activity-quercus-ilex-pinus-halepensis

    As most of the earth is covered by ocean the next questions could be of the UV/VIS -spectrum of water:”How deep under water floating algae can photosynthesize and what is the effect of ozone hole to the primary production on the southern ocean?”

  46. 46
    Saul says:

    There are an interesting suite of anomalies that appear to correlate with solar minimums.

    There is addition to paleoclimatic changes that correlate with deep solar minimums there is a curious increase in worldwide volcanic activity during deep solar minimums. (The anomaly is the increase in volcanic activity is in regions that geographically and geologically separated.)

    Curiously sea level also correlates with solar minimums (sea level falls during solar minimums) with the change in sea level being more than twice what would be expected based on thermal expansion due to temperature change.
    Solar cycle 24 appears based on the change in solar parameters to be an abrupt interruption in the solar magnetic cycle as opposed to a slow down. There is also an interesting suite of anomalies associated with observations related to the solar magnetic field and stellar magnetic fields.

  47. 47
    Jonty says:

    My father is somewhat of a climate ‘sceptic’ and insists that the prediction of 0.3C cooling is based only on solar irradiance and does not take into account increased cloud cover caused by low sun activity (he beleives that we are going to be facing extreme global cooling over the next few decades). Could anyone tell me if he is in any way correct. Thanks.

  48. 48
    ivp0 says:

    An interesting look at our variable sun. The conclusions of -.3C are not consistent with historical evidence, ice core analysis, crude 16th century thermometers, or glacier movement that suggest NH cooling of -2C during Maunder. Since our current warm period is primarily a NH event a Maunder type -2C NH cooling would be dramatic.

    While there is pretty strong evidence to suggest a 1.5C warming by doubling atmospheric CO2, suggesting a +4C by 2100 is speculative at best requiring large assumptions of positive feedbacks that have not been observed to date. I suspect given what we know about radiative physics and what we don’t know about the sun during a prolonged grand minimum it is equally likely that it will be no warmer in 2100 than it is today.

    While considering the possible grand minimum this century we must also consider the effect of the Grand maxima we experienced during the last century and it’s possible contribution to observed warming.

    [Response: There is no synthesis of evidence that supports your claims of such a large change at the Maunder Min. - you are implying a change that is 1/3 of the way to a full blown glacial maximum. Very, very unlikely (about as unlikely as 2100 not being any warmer than today - though that is mainly wishful thinking). - gavin]

  49. 49
    ivp0 says:

    Gavin Says: “There is no synthesis of evidence that supports your claims of such a large change at the Maunder Min. – you are implying a change that is 1/3 of the way to a full blown glacial maximum. Very, very unlikely (about as unlikely as 2100 not being any warmer than today – though that is mainly wishful thinking). – gavin]

    Hmmmm,

    I suspect Dr. Richard Alley would strongly disagree:
    “In the North Atlantic, sediments accumulated since the end of the last ice age nearly 12,000 years ago show regular increases in the amount of coarse sediment grains deposited from icebergs melting in the now open ocean, indicating a series of 2-4ºF (1-2ºC) cooling events recurring every 1,500 years or so. The most recent of these cooling events was the Little Ice Age between 1500-1850 AD when European rivers and ports were choked with ice, and glaciers overran alpine villages.” -Alley

    [Response: I doubt it actually. Alley is talking mainly about D/O events and, like some others (Broecker for instance) tried to link it to the LIA, but neither the pattern of change, the abruptness, the ocean circulation change nor the magnitude actually match. You don't give a date for this quote, but I doubt it is recent. - gavin]

  50. 50
    M says:

    “You don’t give a date for this quote, but I doubt it is recent. – gavin”

    Looks like 1998 to me:
    http://www.usgcrp.gov/usgcrp/seminars/980217DD.html

    -M


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