Guest commentary by Raimund Muscheler
[note: this is a restore (8/8/05) of an article from August 3, 2005 that was accidentally deleted due to a technical glitch. Unfortunately, most of the comments could not be retrieved. We sincerely apologize to our readers!]
The solar influence on climate is a controversial topic in climate research (see previous posts here and here). The irradiance changes are assumed to be relatively small and the importance of potential amplifying mechanisms is still a matter of current debate. One reason for these uncertainties is that there are only approximately 25 years of satellite-based observations of the solar irradiance. Sunspot observations for the last 400 years clearly indicate that current levels of solar activity are very different from the state of the sun during the Maunder minimum (from approx. 1645 to 1715 AD) where almost no sunspots could be observed.
Cosmogenic radionuclides (such as 10Be and 14C) records are the most reliable proxies to extent solar activity reconstructions beyond the period of direct observations of the sun. They are produced in the atmosphere by the interaction of galactic cosmic rays with the atoms of the atmosphere. High solar shielding of the galactic cosmic rays during periods of high solar activity decreases the radionuclide production rates and vice versa for low solar activities. Cosmogenic radionuclide production rates are also influence by the geomagnetic field. Similarly to the solar magnetic modulation, high geomagnetic field intensity decreases the flux of galactic cosmic rays and radionuclide production rates and the opposite for low geomagnetic field intensity.
The processes responsible for the radionuclide production are well known and can be modeled quantitatively. The biggest uncertainties lies in the interpretation of the radionuclide records that can be measured in natural archives such as ice cores in the case of 10Be or tree rings in the case of 14C. This is due to the fact that changes in atmospheric transport and deposition in the case of 10Be or changes in the carbon cycle in the case of 14C can influence the measured concentrations. Unidentified climatic influences lead to errors in the reconstruction of solar activity changes based on these records. This problem is illustrated by two alternative reconstructions of past changes in solar activity based on ice core 10Be records. Based on a 10Be record from Antarctica Bard et al. (2000) conclude that currents levels of solar activity were also reached or exceeded around 1200 AD. By contrast, Solanki et al. (2004) conclude that solar activity during recent decades is exceptionally high compared to the past 8000 years. Their method seems to be confirmed by a 10Be record from Southern Greenland (Dye 3, Beer et al, 1990). However, the two 10Be records from Antarctica and Greenland exhibit big disagreements for the last 55 years which is the main reason for these very different conclusions (Raisbeck and Yiou, 2004).
Obviously, at least one of these records must also be influenced by changes in climate. Since 14C is influenced by completely different geochemical behavior than 10Be, the investigation of 14C records can help to solve the contradictions. Since carbon cycle models allow us to understand past changes in atmospheric CO2 and 13C concentrations it is also possible to use these models to infer the 14C production rate based on measured 14C concentrations in tree rings. Until 1950 AD, when significant amounts of anthropogenic 14C were released into the atmosphere by the nuclear weapons tests, we can calculate the variations in the 14C production rates and infer the solar magnetic modulation from these records. There are uncertainties in connecting the 14C production rate to recent instrumental measurements of solar magnetic modulation (see figure). However, regardless of these uncertainties the conclusions by Usoskin et al. (2003) and Solanki et al. (2004) cannot be confirmed by the analysis of the 14C records (Muscheler et al., 2005). The 14C tree ring records indicate that today’s solar activity is high but not exceptional during the last 1000 years.
Figure 1: Reconstructions of the (11-year smoothed) solar magnetic modulation based on 14C data from tree rings combined with instrumental measurements (Muscheler et al.,2005). The purple curve shows the results according to a normalization using balloon-borne measurements. The black and green curves show results using an alternative normalization and the northern hemisphere (black) and globally averaged (green) 14C data. The red curve is the group sunspot number.
Are there additional proxies that could shed light on the solar history? First of all the sunspot record represents a good proxy for solar variations during the last 400 years. While the group sunspot record indicates high solar activity during the last 60 years compared to the preceding 350 years, the Wolf sunspot record reached today’s values for a short period around 1780 AD (with the exception of the very strong sunspot maximum around 1957 AD). Aurora observations also provide information about the history of the sun. However, there are no systematic observations and therefore the conclusions are uncertain. 44Ti measurements in meteorites have the potential to provide high quality estimates of past changes in solar magnetic modulation but, until now, the data are sparse and exhibit large errors (Castagnoli et al., 2003). 36Cl is another useful cosmogenic isotope, but that too has data quality and bomb contamination problems in the modern period. Therefore, it is not yet possible to draw firm conclusions about solar activity changes during the last 400 years based on these data. To conclude, depending on the applied 10Be record different histories of the sun have been inferred. The 14C tree ring record does not confirm the 10Be record from Southern Greenland and the assertion that recent solar activity levels are exceptional. Alternative estimates of the history of the Sun are not yet good enough to be used as independent checks.
Therefore, in the view of the uncertainties and the conflicting data it doesn’t seem to be appropriate to make uncritical and sensational claims about the history of the sun. As long as the differences between the 10Be records are not understood, conclusions based on only one of these records should be treated with caution. Atmospheric 14C concentrations, on the other hand, are much less sensitive to a climate influence during the last 1000 years and, therefore, can provide good estimates of the history of the sun. However, the disagreement between 14C-based solar activity and group sunspot number (Muscheler et al., 2005) should remind us that the variations of the solar activity are not yet completely understood.
Regardless of any discussion about solar irradiance in past centuries, the sunspot record and neutron monitor data (which can be compared with radionuclide records) show that solar activity has not increased since the 1950s and is therefore unlikely to be able to explain the recent warming.
Bard, E., Raisbeck, G.M., Yiou, F., Jouzel, J., 2000. Solar irradiance during the last 1200 years based on cosmogenic nuclides. Tellus 52B, 985-992.
Beer, J., Blinov, A., Bonani, G., Finkel, R.C., Hofmann, H.J., Lehmann, B., Oeschger, H., Sigg, A., Schwander, J., Staffelbach, T., Stauffer, B., Suter, M., Wölfli, W., 1990. Use of 10Be in polar ice to trace the 11-year cycle of solar activity. Nature 347, 164-166.
Cini Castagnoli, G.C., Cane, D., Taricco, C., Bhandari, N., 2003. GCR Flux Decline during the last Three Centuries: Extraterrestrial and Terrestrial Evidences. In: T. Kajita, Y. Asaoka, A. Kawachi, Y. Matsubara, M. Sasaki. (Eds.), GCR Flux Decline during the last Three Centuries: Extraterrestrial and Terrestrial Evidences, Universal Academy Press, Inc., pp. 4045-4048.
Muscheler, R., Joos, F., Mueller, S.A., Snowball, I., 2005. How unusual is today’s solar activity? Nature 436, E3-E4. (Reply by Solanki et al)
Raisbeck, G.M., Yiou, F., 2004. Comment on ”Millennium Scale Sunspot Number Reconstruction: Evidence for an Unusually Active Sun Since the 1940s”. Physical Review Letters 92, DOI: 10.1103/PhysRevLett.92.199001.
Solanki, S.K., Usoskin, I.G., Kromer, B., Schüssler, M., Beer, J., 2004. Unusual activity of the Sun during recent decades compared to the previous 11,000 years. Nature 431, 1084-1087.
Usoskin IG, Solanki SK, Schussler M, Mursula K, and Alanko K., Millennium-scale sunspot number reconstruction: evidence for an unusually active sun since the 1940s. Phys Rev Lett. 2003, 91(21):211101.
23 Responses to "Did the Sun hit record highs over the last few decades?"
Mike Doran says
The solar change of most significance in these timescales is about it’s electrical particle and field variability.
Here is a great article, which implies the difficulty of design without a living earth theory, on the subject of so called junk DNA:
There are two main aspects of a living earth, the cirrus cloud part,
and the ocean part. The cirrus clouds in pre cellular earth would
have contained nucleotides in such manner as they would 1) replicate
and 2) have an electrical to mass meaning. IOWs, if rain feedbacks/convection feedbacks caused “nutrients” to be available on the ocean surface below, such that the nucleotides could both replicate and replicate with a meaningful mass and charge, you would have a good feedback. As always, there was survival of the individual nucleotide complex and survival of the entity–the living earth. Below in the oceans the nucleotides would contain chemistry over chaotic diffusion of chemicals but that containment was probably not all that significant on conductivities like cellular life is today. Appreciate that the oceans are too saline for the China paper cloud parasol asymmetries to occur in DC fields between ionosphere and ocean . . .
Junk DNA was anything but junk to cirrus cloud formations in pre cellular earth. The function of the DNA was not to produce proteins or regulate or translate them, but rather the nucleotide function was simply to provide an electrical feedback to convection processes that occur w/ cirrus clouds that can trap heat, compress air and cause rain over ambient, lifeless winds and climate inputs. Indeed, the purpose is closely seen in the electropherisis that leads to appreciating that they exist. The cloud parasol feedback is quite powerful, depending on the size, shape, mass and charge of the complex, and, additionally, because of phase change energies on the DNA particles, forming or not, in cloud nucliation processes bring to cloud dynamics significant forcings. See this Tinsley article:
If solar variability due to heat was all that mattered, then life could not have design.
Armand MacMurray says
Thanks for a very nice exposition of some of the issues involved in estimating past solar activity!
I understand that the Group sunspot number extends further back than the Wolf number, but given the striking disagreement between the 14C & Group numbers around 1780 (Fig. 1), would it be better to use the Wolf number?
Mike Doran says
#2 I don’t think the sun mattered much in the Little Ice Age, either, the way it is currently framed. I am much more impressed with a gravity wave theory put out by Charles Keeling from Scripps, who just passed away. See http://www.pnas.org/cgi/content/full/070047197
The data merely lacks causal mechanism as an explaination.
Even the Soon paper work falls short on cause for the sun and admits that there is not proper appreciation of what the earth takes from the sun as opposed to what the sun gives–and that mystery is more appreciated by looking at essentially what is going on from an EMF standpoint between earth and the sun. In that context, gravity waves roil and depressurize the oceans, and that then leads to outgassing of CO2–it comes out of solution in the ocean and bubbles to the surface and their given capacitive couplings impacting pH runs back to ion form–which then impacts conductivity. The conductivity changes impact cloud microphysics, and heat trapped or released out into space. So you could have a paradox of more sun heat coming to the earth and the earth taking less of that heat–it gets released out into space or turned into kinetic energy like a tropical storm, all because of the ELECTRICAL features impacting earth, including some impacts that are not related to the sun, like moon gravity waves.
Presently I am looking at a solar wind speed under 500 that seems to correlate with tropical storm formation. One theory for this is while solar activity leads to increases in high freq light, and that light splits O2 into ozone, and hence increases the ions for couplings between ionosphere and ocean, at the same time particles of protons come to be attracted to opposing charges and the whole organization of van Allen belts, electron shell, proton shell, upper ionosphere, lower ionosphere gets disturbed, and prevents formation of nice coupled states between ionosphere and ocean, above tropical storm eyes. But then the other thing going on is those same protons run to the closing isobars of the earth EMF away from the tropics, and there reduce ozone, and create over time a concentration of ozone over the tropics, thereby increasing the intensity of the ITCZ and increasing tropical storm probabilities, as the wind then wanes under 500. These are the kinds of very complex space weather discussions that need to occur, and at the end of the day CO2 is DEPENDANT on these solar events as CO2 is ELECTRICAL from a conductivity standpoint in the oceans, connected to surface lows and outgassing and ocean surface ion counts.
Stephen Berg says
In Brian Fagan’s “The Little Ice Age,” he cites several paintings and diaries which have stated that the LIA was a period of dull skies (i.e. lack of bright sunshine and increased cloudiness).
The Keeling oceanic tidal cycle article you site deals with 1,800-year cycles and not 200- or 300-year cycles. Keeling also mentions that solar cycles (i.e. Milankovitch Cycles) are multi-millennia-scale. As the LIA lasted only a few centuries, wouldn’t the oceanic tidal cycles be either irrelevant, or at least not individually responsible for the occurrence of the LIA?
Also, as it relates to the AGW discussion, since the oceanic tidal cycle has such a long duration, wouldn’t this cycle be irrelevant, since AGW has only taken hold over the last 150 years and has such a high rate of temperature increase?
As for the whole electrical and space weather business, none of that makes much sense in a global context. The theories that moon gravity waves, ocean ionization, and proton/electron changes could somehow trigger an increase in temperature seems to be quite bizarre to me.
[Response: It is important to remember that paintings and diaries are anecdotal – for instance, Bruegel’s Hunter’s in the Snow is often cited in such a context, but often neglected is that the fact that this was a) a fictional scene, and b) part of a series of seasonal paintings. The Harvesters for instance shows a very sunny and pleasant day. Is that proof of warmer autumns? I don’t think so…. -gavin]
I’m struggling with the earth-bound C14-production series : Is the series shown in Gavin’s ‘lure of solar forcing’ plot at a different stage of [geomag/dilution] correction to the series shown in Fig 2 of the Nature ‘Arising’ comment?
-I’m looking at the relative size of the 1780’s spike.
They seem v different, but perhaps its detrending etc.(or just an error)
Harry Francis says
Might the global warming simply be due to the daily collection of space dust… suggested at over 150 million tons each year…..With increased mass, are we not slowly attracted closer to the sun ?
Andrew Dodds says
Re: #6. Several astronomical factors affect the climate of the earth; the Sun gets brighter over time as it moves along the main sequence, and the Earth gradually drifts further away from the sun as the mass of the sun drops (Solar wind, nuclear conversion). Space dust should have zero net effect, since on average it should have the same orbit as the earth to start with.
However, it has to be realised that the above effects work on timescales of a minimum of 10 million years, and are only detectable at timescales longer than that. If astronomical factors were capable of producing a trend on human timescales, we’d have baked or frozen a long, long time ago.
Raimund Muscheler says
The 14C production rate record shown in ‘lure of solar forcing’ basically agrees with the record shown in this discussion. The difference is:
I. The older calculation (Muscheler ETH PhD2000, Muscheler et al., QSR 2005) covers the Holocene period using the IntCal98 D14C record.
II. The new calculation (Muscheler et al., Nature 2005) uses the annual 14C record measured by Minze Stuiver et al.. In addition, we included the Suess effect (the dilution of 14C in the atmosphere due to the combusion of 14C-free fossil fuel). This is important for the period from 1850 to 1950 yr AD and allowed us to connect the 14C production series to the instrumental measurements of the galactic cosmic ray flux.
Please note that, in general, the different 14C production rate estimates agree well (Minze Stuiver was the first to do these kind of calcuations). The results depend only slightly on the applied carbon cycle model.
The 14C production rate minimum around 1780 yr AD (-> high solar activity) follows from a strong minimum in the D14C data from the northern hemisphere (it is visible in the annual D14C data and in the new IntCal04 calibration record). However, the minimum is smaller in the D14C record from the southern hemisphere. Therefore, I think the peak around 1780 yr AD rather overestimates solar activity. The 10Be record from Antartica indicates that the 1780 yr AD maximum is on a similar level as around 1950 yr AD. Within the uncertainties this is still in agreement with the 14C data.
Mike Doran says
Alec Rawls says
Nice post, but the conclusion: “… solar activity has not increased since the 1950s and is therefore unlikely to be able to explain the recent warming,” would seem to be a non-sequitur.
What matters is not the trend in solar activity but the level. It does not have to KEEP going up to be a possible cause of warming. It just has to be high, and it has been since the forties.
Presumably you are looking at the modest drop in temperature in the fifties and sixties as inconsistent with a simple solar warming explanation, but it doesn’t have to be simple. Earth has heat sinks that could lead to measured effects being delayed, and other forcings may also be involved. The best evidence for causality would seem to be the long term correlations between solar activity and temperature change. Despite the differences between the different proxies for solar activity, isn’t the overall picture one of long term correlation to temperature?
[Response: You are correct in that you would expect a lag, however, the response to an increase to a steady level of forcing is a lagged increase in temperature and then a asymptotic relaxation to the eventual equilibirum. This is not what is seen. In fact, the rate of temperature increase is rising, and that is only compatible with a continuing increase in the forcing, i.e. from greenhouse gases. – gavin]
Ilya Usoskin' says
The commentary by Raimund Muscheler presents quite a one-sided view on the problem.It is based on their Comment to our paper in Nature (2004). However next to their Comment, our official reply (Solanki et al.,Nature, 436, E4-E5, doi:10.1038/nature04046, 2005) has been published which is ignored in Muscheler’s commentary. We urge the reader to get acquainted also with our point of view before making any conclusion.
Muscheler et al. (2005) tried to reproduce our reconstruction (Solanki et al., 2004) of solar activity from 14C but in a different way and obtained a different result. Note that the details of how the results were obtained have not been published.Accordingly, their computation cannot be repeated and verified independently. In contrast, our approach has been developed and verified in a number of papers (Solanki et al., Nature, 408, 445, 2000; Solanki et al., Astron. Astrophys., 383,706, 2002; Usoskin et al., J. Geophys. Res.. 107(A11), 2002; Usoskin et al., Phys. Rev. Lett., 91(21), 211101, 2003; Usoskin et al., Astron. Astrophys., 413, 745, 2004; Solanki et al., Nature, 431, 1084, 2004; Usoskin and Kromer, Radiocarbon,47(1), 31, 2005) which contain full details of the method. Muscheler et al. did not find any error in our method while we brought to light a serious flaw in Muscheler et al. (2005) which causes the disagreement between his and our result. Briefly, their method produces only relative variations of cosmic ray flux. In order to
discuss the absolute level of reconstructed solar activity, they normalized it to the measured values during 20th century (a free parameter of the model). Unfortunately, when performing the normalizing procedure, they made use of an inappropriate data set, from which the long-term trend has been implicitly removed (see details in Solanki et al., 2005). This resulted in a distorted long-term trend in their reconstruction. When using the correct data set (called “alternative” by Muscheler et al., 2005), they obtained the results which are very similar to ours as the purple curve in Muscheler’s Fig.1 is close to our solar activity reconstruction from 14C (see Solanki et al., 2004). All other curves in Muscheler’s Figure are affected by this normalization flaw which is seen as a constant offset between the curves (all curves are parallel to each other before 1950). Actually, this large difference of about 300 MV between purple and green curves serves as their model uncertainties.
Briefly, Muscheler, using a different (unpublished and unverified) method, obtained a result which differs from our results. We don’t think that just this difference provides a substantial basis to claim that our results are wrong.
Richard Harvey says
Couldn’t the question of attributing the recent warming to a solar influence be answered by looking at the 3D distribution of the *signature* of that warming? For instance, the nighttime temperature minimums have increased at about twice the rate of daytime maximums. If the sun had been the main cause of global warming, this trend should have been reversed, i.e., daytime maximums increasing faster. From this fact alone, the sun just can’t be the cause.
Brent Putnam says
John Finn made some interesting observations in his post. Unfortunately, that was lost because of the “technical glitch.” Fortunately, I found them in a cached copy. Here they are, complete with responses from Mike and Gavin:
Response: It is important to remember that paintings and diaries are anecdotal…
[Response: Comments such as yours which cherry-pick the available evidence (see below–we point out a few glaring examples to make the more general point. We could have gone on…) to the point of disinforming, rather than educating, our readers will not be tolerated on “RealClimate”. We let this one through, but other similar future postings will be deleted. -mike]
Absolutely right. So-called evidence from Art and Literature cannot be accepted as an indication that a Little Ice Age existed and there is therefore no proof whatsoever. Well – apart from the Central England Temperature record
which shows that temperatures (10 year running mean) in the late 17th century were 2 degrees colder than they were just 40 years later, but that’s obviously a local blip which we can ignore.
[Response: For most of the pre-20th century (1650-1900) interval, the CET record shows very little change at all. Do you really believe that citing one isolated 30 or so year period of cooling within that record that occurs during the late 17th century defines “The Little Ice Age”? You should read the background material already provided on RealClimate, especially our correction of some common myths and half-truths (see myth#2). -mike]
Ok – perhaps we shouldn’t forget how some Keigwin chap showed that the Saragossa Sea was ~1 deg colder ~ 400 years ago
[Response: Unfortunately, you seem to have conveniently forgotten that Keigwin (and Pickart) published a paper in Science just a few years later in 1999 pointing that the appparent cooling (actually, the oxygen isotopic signal in question isn’t entirely temperature, it is salinity as well, so the quantative 1 deg cooling estimate you cite is not actually reliable) in the Sargasso Sea is diametrically opposed by a substantial warming at the same time in the Laurentian Fan region of the North Atlantic off the coast of Newfoundland. The pattern of cooling in the tropical North Atlantic and warming off Newfoundland, as Keigwin and Pickart note, is consistent with a dominant North Atlantic Oscillation (NAO) signature to the climate variability in this region during the MWP/LIA alternation. Modeling work published by members of the RealClimate group supports this conclusion. See e.g. this review paper (Schmidt et al, 2004), where the response of a climate model to estimated past changes in natural forcing due to solar irradiance variations and explosive volcanic eruptions, is shown to match the spatial pattern of reconstructed temperature changes during the “Little Ice Age” (which includes enhanced cooling in certain regions such as Europe). This patterns is shown to be in large part a product of an extended negative phase of the NAO. The model also matches well the smaller estimated hemispheric-mean changes, which typically represent a cancellation of larger regional patterns of warming and cooling associated with processes such as the NAO. -mike]
And while we’re at it it might just be worth mentioning that part of North America seems to have had a LIA (and MWP) as well according to this
But apart from that – nothing ….unless you include South America, of course
Villalba, R., “Tree-ring and Glacial Evidence for the Medieval Warm Epoch and the Little Ice Age in Southern South America”. Climate Change, 26:183-197, 1994
And …er ….South Africa
Tyson, P.D. et al., “The Little Ice Age and Medieval Warming in South Africa”. South African Journal of Science, 96:121-126, 2000
But that’s definitely it. Once you discount other studies from China, the Caribbean, sub-saharan Arica, Japan and one or two other locations, there’s not a single shred of evidence left to suggest that the Little Ice Age was anything other than a figment of the rather fertile imagination of artists and writers.
[Response: Well that seems to have touched a nerve! As you are climbing down from your high horse please remember that a) I never implied that the temperatures were not colder, just that winter paintings are not proof that they were not colder, b) I have written at least three papers concerning the cooling during the Little Ice Age (well Maunder Minimum), and so presumably I do think that it exists. However, there are still significant issues about the spatial pattern of cooling and dating of some of the records you mention. But as a general point, scientific disccusion concerns the specifics of each issue, and not jumping to conclusions about what people assume that you are implying. Please keep it focussed. -gavin]
Comment by John Finn – 5 Aug 2005 @ 10:36 am
Re #11 Is the Fig.1 you refer to, also, Fig.2b in RM’s Nature comment?
Re #8 Thank you for clarifying the reasons for the difference.
I am pretty sure the sun will continue to get hotter as time goes on adn not the other way around atleast for another million or so years.
Hans Erren says
What information do you have to support this claim? We are interested in the next hundred years, and here the small fluctuations are important as the maunder minimum clearly demonstrates.
Steve Latham says
Re 15 & 16, I have noticed that some comments are meaningless attempts to get you to click and go to a website promoting something or other. (The last two comments on the Acid Ocean posting are examples; click on the highlighted portion and go to a back pain website.)
Hank Roberts says
Has anyone yet talked up designing a Mars lander that would be able to drill a core from the polar ice cap, scan it and give us another data set?
(I wonder if the lunar ice at the poles would have any use as a time series indicator of solar activity, too)
Stephen Berg says
“University Of Oregon Study Says Sunnier Oregon Summers Reflect Global Warming”:
Brendon Boyce says
Could the increasing temperature of the Earths surfact be-even in the sligthest-due to increasingly stronger CME’s (Coronal Mass Ejections) due to the fact that these stronger CME’s have been known to be so intense that they penitrated the magnetosphere and have burnt out large power plants. Could some of this power along with heat not also contribute to the increase in tempatuer. More of the ‘left over’ plasma is getting caught in the Earth’s atmosphere helped along by the fact the the atmosphere is being continoust polluted at an expontial rate compared to when we first started recording the number of CME’ along with sunspots
Steve Bloom says
Re #15 and #16: Very roughly, the total insolation change over the Sun’s approximately 8 billion years on the main sequence will be from about 75% of current to about 135% of current. So, divide 60 by 8 billion for the average percentage change for a year. Even for a million years, the change is still less than 1/100th of 1% (relative to current levels). A century’s worth of change in turn would be less than 1/1,000,000th of 1%, which is to say below any possible level of significance. The short-term variance is vastly greater.