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How we know the sun isn't causing global warming

Posted on 9 September 2010 by dana1981

The Sun's largest influence on the Earth's surface temperature is through incoming solar radiation, also known as total solar irradiance (TSI).  Changes in TSI can be converted into a radiative forcing, which tells us the energy imbalance it causes on Earth.  This energy imbalance is what causes a global temperature change.

The solar radiative forcing is TSI in Watts per square meter (W-m-2) divided by 4 to account for spherical geometry, and multiplied by 0.7 to account for planetary albedo (Meehl 2002).  The albedo factor is due to the fact that the planet reflects approximately 30% of the incoming solar radiation.

dF = 0.7 * d(TSI)/4

This is a very straightforward and easy to understand formula - the larger the change in solar irradiance, the larger the energy imbalance it causes, and thus the larger the radiative forcing.  Studies have reconstructed TSI over the past 300 years.  Wang, Lean, and Sheeley (2005) compared a flux transport model with geomagnetic activity and cosmogenic isotope records and to derive a reconstruction of TSI since 1713.

Wang 2005

Figure 1: Total Solar Irradiance from 1713 to 1996 (Wang 2005)

Satellites have directly measured TSI since 1978.


Figure 2: Total Solar Irradiance as measured by satellite from 1978 to 2010

As you can see, over the past 32 years, TSI has remained unchanged on average.  In the early 20th century, from about 1900 to 1950 there was an increase in TSI from about 1365.5 to 1366 W-m-2.  The change in global temperature in response to a radiative forcing is:

dT = ?*dF 

Where 'dT' is the change in the Earth's average surface temperature, '?' is the climate sensitivity, usually with units in Kelvin or degrees Celsius per Watts per square meter (°C/[W-m-2]), and 'dF' is the radiative forcing.

So now to calculate the change in temperature, we just need to know the climate sensitivity. Studies have given a possible range of values of 2 to 4.5°C warming for a doubling of CO2 (IPCC 2007), which corresponds to a range of 0.54 to 1.2°C/(W-m-2) for ?.  We can then calculate the change in global temperature caused by the increase in TSI since 1900 using the formulas above.  Although Wang, Lean, and Sheeley's reconstruction puts the change in TSI since 1900 at about 0.5 W-m-2, previous studies have shown a larger change, so we'll estimate the change in TSI at 0.5 to 2 W-m-2.

dF = 0.7 * d(TSI)/4  = 0.7*([0.5 to 2 W-m-2]/4) = 0.1 to 0.35 W-m-2

This matches up well with the IPCC solar forcing range of 0.06 to 0.30 W-m-2, with a most likely value of 0.12 W-m-2.  We can then calculate the associated surface temperature change:

dT = ?*dF = (0.1 to 0.35 W-m-2)*(0.54 to 1.2°C/[W-m-2]) = 0.05 to 0.4°C, with a most likely value of 0.15°C.

We can confirm this by comparing the calculation to empirical observations.  From 1900 to 1950 the Earth's surface temperature warmed by approximately 0.4°C.  Over that period, humans increased the amount of carbon dioxide in the atmosphere by about 15 parts per million by volume (ppmv), from approximately 295 to 310 ppmv.  This corresponds to an anthropogenic warming of:

dT = ?*dF = 5.35*(0.54 to 1.2°C/[W-m-2]*ln(310/295) = 0.14 to 0.32°C with a most likely value of 0.22°C.

Therefore, the solar forcing combined with the anthropogenic CO2 forcing and other minor forcings (such as decreased volcanic activity) can account for the 0.4°C warming in the early 20th century, with the solar forcing accounting for about 40% of the total warming.  Over the past century, this increase in TSI is responsible for about 15-20% of global warming (Meehl 2004).  But since TSI hasn't increased in at least the past 32 years (and more like 60 years, based on reconstructions), the Sun is not directly responsible for the warming over that period.

Indirect Solar Effects

Ultraviolet Radiation

It has also been proposed that ultraviolet (UV) radiation, which varies more than other solar irradiance wavelengths, could amplify the solar influence on the global climate through interactions with the stratosphere and atmospheric ozone.  Shindell et al. (1999) examined this possibility, but found that while this UV variability has a significant influence over regional temperatures, it has little effect on global surface temperatures.

"Solar cycle variability may therefore play a significant role in regional surface temperatures, even though its influence on the global mean surface temperature is small (0.07 K for December–February)."

Moreover, Shindell et al. found that anthropogenic ozone depletion (via chlorofluorocarbon emissions) may have reduced the impact of UV variability on the climate, and may have even offset it entirely.

"Another consideration is that upper stratospheric ozone has decreased significantly since the 1970s as a result of destruction by halogens released from chlorofluorocarbons.  This ozone decrease, which has been much larger than the modeled solar-induced ozone increases, may have limited the ability of solar irradiance changes to affect climate over recent decades, or may have even offset those effects."

Galactic cosmic rays

Henrik Svensmark has proposed that galactic cosmic rays (GCRs) could exert significant influence over global temperatures (Svensmark 1998).  The theory goes that the solar magnetic field deflects GCRs, which are capable of seeding cloud formation on Earth.  So if solar magnetic field were to increase, fewer GCRs would reach Earth, seeding fewer low-level clouds, which are strongly reflective.  So an increased solar magnetic field can indirectly decrease the Earth's albedo (reflectivity), thus causing the planet to warm.  Thus in order for this theory to be plausible,

  1. Solar magnetic field must have a long-term positive trend.
  2. Galactic cosmic ray flux on Earth must have a long-term negative trend.
  3. Cosmic rays must successfully seed low-level clouds.
  4. Low-level cloud cover must have a long-term negative trend.

Fortunately we have empirical observations with which to test these requirements.

Solar magnetic field

Solar magnetic field strength correlates strongly with other solar activity, such as TSI and sunspot number.  As is the case with these other solar attributes, solar magnetic field has not changed appreciably over the past three decades (Lockwood 2001).

Lockwood 2001 

Figure 3: Solar Magnetic Flux from 1850 to 2001

Galactic Cosmic Ray Flux

Cosmic ray flux on Earth has been monitored since the mid-20th century, and has shown no significant trend over that period.

cosmic ray flux

Figure 4: Cosmic Ray Intensity (blue) and Sunspot Number (green) from 1951 to 2006 (University of New Hampshire)

GCR Cloud Seeding

Numerous studies have investigated the effectiveness of GCRs in cloud formation.  Kazil et al. (2006) found:

"the variation of ionization by galactic cosmic rays over the decadal solar cycle does not entail a response...that would explain observed variations in global cloud cover"

Sloan and Wolfendale (2008) found:

"we estimate that less than 23%, at the 95% confidence level, of the 11-year cycle changes in the globally averaged cloud cover observed in solar cycle 22 is due to the change in the rate of ionization from the solar modulation of cosmic rays."

Kristjansson et al. (2008) found:

"no statistically significant correlations were found between any of the four cloud parameters and GCR"

Calogovic et al. (2010) found:

"no response of global cloud cover to Forbush decreases at any altitude and latitude."

Kulmala et al. (2010) also found

"galactic cosmic rays appear to play a minor role for atmospheric aerosol formation events, and so for the connected aerosol-climate effects as well."

Low-Level Cloud Cover

Unfortunately observational low-level cloud cover data is somewhat lacking and even yields contradictory results.  Norris et al. (2007) found

"Global mean time series of surface- and satellite-observed low-level and total cloud cover exhibit very large discrepancies, however, implying that artifacts exist in one or both data sets....The surface-observed low-level cloud cover time series averaged over the global ocean appears suspicious because it reports a very large 5%-sky-cover increase between 1952 and 1997. Unless low-level cloud albedo substantially decreased during this time period, the reduced solar absorption caused by the reported enhancement of cloud cover would have resulted in cooling of the climate system that is inconsistent with the observed temperature record."

So the jury is still out regarding whether or not there's a long-term trend in low-level cloud cover.

Inability to explain other observations

In addition to these multiple lines of empirical evidence which contradict the GCR warming theory, the galactic cosmic ray theory cannot easily explain the cooling of the upper atmosphere, greater warming at night, or greater warming at higher latitudes.  These are fingerprints of the increased greenhouse effect, the major mechanism of anthropogenic global warming.

Dansgaard-Oeschger Events

Some individuals, most notably Fred Singer, have argued that Dansgaard-Oeschger (D-O) events could be causing the current global warming.  D-O events are rapid climate fluctuations that occur quasi-periodically with a 1,470-year recurrance time and which, according to Singer, are "likely caused by the sun."  However, there is significant debate as to the cause of these D-O events, with changes in solar output being just one possibility (NOAA Paleoclimatology).

Regardless, the most obvious flaw in this argument is that the planet wasn't warming 1,470 years ago.  The previous warm event was the Medieval Warm Period approximately 1,000 years ago.

Figure 5: Global temperature reconstructions over the past 2,000 years (Globalwarmingart)

Bond et al. (1999) added further evidence that the timing of D-O events disqualifies them from being responsible for the current warming, by showing that the most recent D-O event may have contributed to the Little Ice Age (LIA):

"evidence from cores near Newfoundland confirms previous suggestions that the Little lce Age was the most recent cold phase of the 1-2kyr cycle"

And a study by Rahmstorf (2003) also concludes that the LIA may be the most recent cold phase of the D-O cycle, and his research suggests that the 1,470-year periodicity is so regular that it's more likely due to an orbital cycle than a solar cycle.

"While the earlier estimate of ±20% [Schulz, 2002] is consistent with a solar cycle (the 11-year sunspot cycle varies in period by ±14%), a much higher precision would point more to an orbital cycle. The closest cycle known so far is a lunar cycle of 1,800 years [De Rop, 1971], which cannot be reconciled with the 1,470-year pacing found in the Greenland data. The origin of this regular pacing thus remains a mystery."

However, according to Braun et al. (2005), D-O events could be caused by a combination of solar cycles and freshwater input into the North Atlantic Ocean.  But their study also concludes that D-O events are not expected to occur during the Holocene (the current geologic epoch).

"the 1,470-year climate response in the simulation is restricted to glacial climate and cannot be excited for substantially different (such as Holocene) boundary conditions...Thus, our mechanism for the glacial ,1,470-year climate cycle is also consistent with the lack of a clear and pronounced 1,470-year cycle in Holocene climate archives."

The bottom line is that regardless of whether or not the D-O cycles are triggered by the Sun, the timing is clearly not right for this cycle to be responsible for the current warming.  Particularly since solar output has not increased in approximately 60 years, and has only increased a fraction of a percent in the past 300 years, as discussed above.

Ironically, prior to publishing a book in 2007 which blamed the current warming on D-O cycles, Singer argued that the planet wasn't warming as recently as 2003.  So the planet isn't warming, but it's warming due to the D-O cycles?  It's quite clear that in reality, neither of these contradictory arguments is even remotely correct.

Inability to explain empirical observations

Aside from the fact that solar effects cannot physically explain the recent global warming, as with GCRs, there are several empirical observations which solar warming could not account for.  For example, if global warming were due to increased solar output, we would expect to see all layers of the atmosphere warm, and more warming during the day when the surface is bombarded with solar radiation than at night.  Instead we observe a cooling of the upper atmosphere and greater warming at night, which are fingerprints of the increased greenhouse effect.

It's not the Sun

As illustrated above, neither direct nor indirect solar influences can explain a significant amount of the global warming over the past century, and certainly not over the past 30 years.  As Ray Pierrehumbert said about solar warming,

“That’s a coffin with so many nails in it already that the hard part is finding a place to hammer in a new one.”

This post is the Advanced version (written by dana1981) of the skeptic argument "It's the sun". There is also a basic version.

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Comments 1 to 50 out of 81:

  1. Unless I am misreading the above, this blog entry is of rather poor quality. For example, there is the glaring omission of "The Sun and the Earth’s Climate" by Joanna D. Haigh: Joanna D. Haigh, "The Sun and the Earth's Climate", Living Rev. Solar Phys. 4, (2007), 2. URL (cited on Sep 8, 2010): Dr Haig is well known in the field, and references to her work appear at least four times in AR4-WG1-Chapter2. Her last sentence? "Perhaps when these questions are answered we will be confident that we really understand how changes in the Sun affect the climate on Earth". Furthermore, and notably, AR4 classifies the “level of scientific understanding” for Solar Irradiance is “Low”, and for the component linked to cosmic UV rays as “Very low”. It then proceeds to mark the solar forcing estimate as "moderately confident". All these nuances appear nowhere in dana1981's text. Given also that in the first section of the blog entry above there is no mention of scientific articles published after the publication of AR4, its conclusions appear to be unwarranted.
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  2. I love Pierrhumbert's concluding description! "Coffin with so many nails in it...". But the truly amazing thing about it is that so few realize that it already has all these nails. Perhaps the basic version will do something about that. And yes, 'omnologos' should change his moniker to 'amnologos', since yes, he really is missing a lot in the post. Just as the concluding description says: there are so many nails in it is is hard to know where to put a new one. Yet 'omnologos' missed them all, to come up with thei red herring about uncertainty concerning solar radiation.
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  3. omnologos - Although this is the advanced version, the influence of the sun on recent global warming is actually pretty straightforward: there is NO trend over the last 30 years in any of the known solar factors that might influence climate. Whether we're talking about total solar irradiance (the most direct), solar open flux and cosmic rays (different from UV), sunspots, or cycle length, there's simply no trend, whereas temperatures have shot up rather substantially and anomalously in such a short period. Temperature doesn't just change by itself - it has to be forced. There's still a lot to learn about how the solar influence is amplified by various feedbacks, although the response due to the solar cycle gives us some bounds to work with. Galactic cosmic rays are interesting to consider, but we know relatively little about their influence (especially compared to the vast amount of knowledge regarding greenhouse gas forcing). But again, our understanding of the details is pretty much trumped by the fact that nothing about the sun has changed during the most recent period of global warming. Lockwood and Frohlich (2007) sum it pretty well: "Our results show that the observed rapid rise in global mean temperatures seen after 1985 cannot be ascribed to solar variability, whichever of the mechanisms is invoked and no matter how much the solar variation is amplified." In other words, this isn't about our "low level of scientific understanding", it's just that the sun has to do something if we are to attribute recent warming to it. It hasn't. -Alden
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  4. Good responses by Matt and Alden. I'll just add that despite the 'low' level of understanding, the IPCC also assigned a possible solar radiative forcing range of 0.06 to 0.30 Watts per square meter. In other words, at most the solar radiative forcing is one-fifth as large as the forcing from CO2 alone. As the other commenters noted, although we don't have a great understanding as to every way the Sun influences the global climate, if solar activity isn't increasing, it's not causing global warming.
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  5. I just realized that my estimated range of solar forcing at 0.1 to 0.35 W m-2 is very close to the IPCC range. That's pretty cool, and a bit of a relief since I didn't think to check it after doing the calculation.
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  6. Not sure what the replies above are about. For example, Raypierre's non-peer-reviewed comments surely can't be put on the same level as peer-reviewed work? Let's go back to my points. The omission of Haigh's 2007 paper is even more glaring given that the first section of the blog mentions works of 2002, 2004 and 2005, plus AR4. Here's some other work of hers around that timeframe, again not referred to by the blog entry above: Gray, L.J., J.D. Haigh, and R.G. Harrison, 2005: Review of the Influences of Solar Changes on the Earth’s Climate. Hadley Centre Technical Note No. 62, Met Office Haigh, J.D., 2003: The effects of solar variability on the Earth’s climate. Phil. Trans. R. Soc. London Ser. A, 361, 95–111. Furthermore, Haigh (2007)'s conclusions are pretty clear. And she already deals with the objection "there is NO trend over the last 30 years in any of the known solar factors that might influence climate" by writing in her abstract: "it is difficult to explain how the apparent response to the Sun, seen in many climate records, can be brought about by these rather small changes in radiation" Here's also some quotes from AR4-WG1-Chapter2: "empirical results since the TAR have strengthened the evidence for solar forcing of climate change by identifying detectable tropospheric changes associated with solar variability, including during the solar cycle" "It is now well established from both empirical and model studies that solar cycle changes in UV radiation alter middle atmospheric ozone forcing appears to induce a significant lower stratospheric response (Hood, 2003), which may have a dynamical origin caused by changes in temperature affecting planetary wave propagation, but it is not currently reproduced by models" ===== So in 2007 there was some work to do...this is what science at the time said, and this is exactly what the IPCC reported. Does anybody know of any peer-reviewed work on the overall topic of the sun's influence on global warming, updating AR4 and Haigh (2007), either confirming or refuting her statements? ======== Say, can't we even agree on taking AR4 as reference? The impression is that we're back in "more royalist than the king" territory...published science is telling us "we don't know enough", yet the blog post boldly states "we know it isn't the sun". Hardly what is expected from a website where science should be in command.
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    Response: Some peer-reviewed research since the IPCC 2007 report:
    • Erlykin 2009: "We deduce that the maximum recent increase in the mean surface temperature of the Earth which can be ascribed to solar activity is 14% of the observed global warming."
    • Benestad 2009: "Our analysis shows that the most likely contribution from solar forcing a global warming is 7 ± 1% for the 20th century and is negligible for warming since 1980."
    • Lockwood 2008: "It is shown that the contribution of solar variability to the temperature trend since 1987 is small and downward; the best estimate is -1.3% and the 2? confidence level sets the uncertainty range of -0.7 to -1.9%."
    • Lean 2008: "According to this analysis, solar forcing contributed negligible long-term warming in the past 25 years and 10% of the warming in the past 100 years..."
    • Lockwood 2008: "The conclusions of our previous paper, that solar forcing has declined over the past 20 years while surface air temperatures have continued to rise, are shown to apply for the full range of potential time constants for the climate response to the variations in the solar forcings."
  7. What exactly is meant by the following: "... divided by 4 to account for spherical geometry" (in the second paragraph)? Can somebody explain this to me? I have higher education in math and physics, so I should be able to understand an explanation - it's just that I need a clue to where the 'universal constant of 4' comes from.
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  8. Argus, TSI is measured in a plane perpendicular to the earth-sun axis. In this plane, the area of illumination is a circle with area (pi r^2). However, when incident on the earth it is distributed over the spherical surface area of the earth, with area (4 pi r^2).
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  9. ◦Erlykin 2009: 14% ◦Lockwood 2008: -1.3% +/- -0.7 to -1.9% That's a a huge spread of variability if you stop to think about it. Do we understand insolation quite as well as we think we do? 14% -> less than zero in a system acknowledged to have multiple sensitive feedbacks is an awful lot of variability with major implications for climate models and mitigation strategies.
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  10. Thank you Ned, for a quick and clear answer! My thoughts concern the fact that most of earth's surface is ocean, and that a water surface has a varying reflectance (or reflectivity), which is depending on the angle of incidence. For an angle of 60 degrees the reflectivity is still less than 0.1, but for 80 it's almost 0.4 (then rising up towards 1.0). This means that not all of the incoming light (and infrared, etc?) is absorbed, which is what 'divided by 4' is presupposing. Actually a reflectivity of 0.0 is assumed for all angles of incidence. Maybe the constant should be around 4.5 instead? Or even 5?
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  11. Hi, chriscanaris. Erlykin 2009 find that solar irradiance (and cosmic ray flux, for that matter) could explain at most 14% of the warming since 1956. It's an upper bound, not a best estimate. They don't attempt to come up with an actual estimate of the magnitude of warming attributable to TSI or CRF, just that for the period 1956-present it has to be less than 14% of the observed warming. You also want to keep in mind the difference in time periods. As noted above, some of the papers do find non-negligible values for the influence of solar irradiance on temperatures prior to the 1970s. But they pretty much all are in agreement that it's essentially zero since then.
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  12. Argus, you're right that spectral reflectance varies as a function of incidence angle. In the analysis presented in this thread, the author simplifies this with the assumption of an overall average albedo of 0.3, or an absorptance of 0.7 (that's where the "0.7" comes from in the equation dF = 0.7 * d(TSI)/4 way up at the top). That's probably good enough for a nonspatial model like this. If you want to look at the energy balance of a particular point on the Earth's surface over time, then you're absolutely correct -- you might have to take into account variance in reflectance as a function of solar elevation angle.
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  13. I shall read with keen interest the links put in the response to #6. In the meanwhile, my original point has now been reinforced. This blog entry's text needs to be edited and the more up-to-date works added to it.
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    Response: We have 3 different rebuttals to the "It's the sun" argument. This blog post is the Advanced version. All the papers posted in that earlier response come from the Intermediate version which features a fairly extensive list of peer-reviewed papers on the solar influence on climate. The Basic version hits the subject in a very brief, simple manner. Something for everyone.
  14. Ned @ 11 Fair point :-)
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  15. regarding the response to #13 So the Advanced Version contains fewer references than the Intermediate one? Go figure!
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    Response: I guess my intermediate version is a broadbrush approach - just listing just about every paper on the topic with a single quote, while the advanced version picks a few papers to go into more indepth analysis. Then the basic version is the cliff notes version :-)
  16. However, Ned, I do think we ought to go back to Haigh's 2007 paper where she argues inter alia: 'Thus a better estimate of radiative forcing to solar irradiance changes should incorporate the effects of the influence of variations in UV on stratospheric temperature and composition (as first noted by Haigh, 1994).' This seems to be one divergence between dana1981 and Haigh who further writes: 'Recently an atmosphere-ocean GCM with fully coupled stratospheric chemistry has been run (despite huge computational demands) to simulate the effects of changes in solar irradiance between the Maunder Minimum and the present (Shindell et al., 2006). As in the previous studies the results show a weakened Hadley circulation when the Sun is more active, and they also suggest an impact on the hydrological cycle with greater tropical precipitation. Furthermore, they provide additional evidence that coupling with stratospheric chemistry enhances the solar signal near the surface.' Moreover: 'There is some observational evidence that variations in the strength of the polar vortex in the upper stratosphere may subsequently influence surface climate. A study of polar temperature trends by Thompson et al. (2005) suggests a downward influence, and modelling experiments by Gillett and Thompson (2003) demonstrate that depletion of stratospheric ozone over the south pole can affect the troposphere after about one month. Neither of these studies is specifically concerned with a solar influence but the accumulating evidence suggests that any factor influencing the strength of the polar stratospheric jet may be able to influence surface climate, at least at high latitudes.' I don't want to turn this into a quote mining exercise. To be perfectly honest, evaluating the claims and reconciling the seeming divergence between two thorough looking summaries of the literature, ie, dana1981 and Haigh (2007) is beyond me. But I'd be interested in hearing what others think on this score. As best as I can tell, Haigh seems to be saying that the sun keeps doing things to climate (or 'weather' if you prefer) at, to use an analogy from another discipline, the 'microeconomic' level while the papers cited in dana's response to omnologos seem to make a 'macroeconomic' assessment. I guess the question then is, is it valid to brush aside the microeconomic perspective or does this risk detracting substantially from our the macroeconomic perspective? Bear in mind that earlier posts have alluded to numerous sensitive feedbacks that go way beyond CO2 rises as causes for concern (eg, CH4 clathrate release and the like).
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  17. Judith Lean has another recent paper on this subject: Lean 2010, Cycles and trends in solar irradiance and climate, Wiley Interdisciplinary Reviews: Climate Change, 1: 111–122. The one-sentence quote that captures its point: Although solar irradiance cycles impart only modest global mean surface temperature changes (of ∼0.1°C), they are nevertheless sufficient to alter climate ‘trends’ on decadal time scales and must therefore be understood and quantified for more reliable near-term climate forecasts and rapid detection of the anthropogenic component to aid global change policy making. In other words, looking forward, at decadal time scales the solar cycle will tend to produce an oscillation in global temperatures that is superimposed on the underlying anthropogenic warming trend. Over the course of each solar cycle, this will alternately amplify the underlying anthropogenic warming trend for a few years, then retard it for a few years.
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  18. The preceding paragraph is also important: 'Dismissal of Sun–climate associations was, until recently, de rigueur because climate models were not been able to replicate them. But the increasingly extensive, broadly self-consistent empirical evidence accruing in multiple high-fidelity datasets of present and past climate, combined with new appreciation of the complex mechanisms, now precludes this. Climate models are instead challenged to reproduce this comprehensive empirical evidence.' This does not, repeat not, mean, 'Great, lets burn more coal folks!'
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  19. chriscanaris, your "macroeconomic / microeconomic" analogy is probably a good one but for some reason I'm not quite getting it. I think we need to be careful to differentiate among various possible questions. (1) Does solar variation have any significant effects on climate? A lot of the material in both Haigh 2007 and Lean 2010 (both of which are fairly long review articles) is about demonstrating the influence of solar variations on aspects of the climate system. And they both convincingly document those influences. If you're a climate modeler, you want to understand those effects. If you're trying to evaluate changes in the climate system among periods when the sun has been more vs less active, you want to understand those effects. (2) Does solar variation "explain away" the multidecadal observed warming trend (say 1975-present)? The question addressed in this thread here at SkS (and in Raypierre's "nails in the coffin" quote) is different, and I think more directly focused on the concerns of skeptics vis-a-vis climate change. The answer to this question appears to be pretty clearly "No, solar variation doesn't explain the underlying warming trend over the past three or four decades". The warming has now continued across multiple solar cycles. Insofar as there is a long-term trend outside of those cycles, we'd expect the sun to be promoting slight cooling rather than warming in recent decades. For a different analogy, consider some kind of migratory animal, like a sandhill crane or something that's heading south for the winter (it's that time of year here in the northern hemisphere...) There is an underlying impetus to keep heading south as winter approaches. But superimposed on that southward migration, the bird moves around its local vicinity in search of food, places to roost for the night, its fellow cranes, etc. So you can't understand the actual movement of this bird without considering the factors that cause the crane to go a little bit east today, and a bit southwest tomorrow, and then north the following day. But those factors (the bird's immediate needs) don't explain why after a period of a month or two it's hundreds or thousands of km south of where it started. OK, maybe your macro/micro economics analogy is better. But at least I think this is a more useful "bird" analogy than BP's dropping some kind of bird out of the leaning tower of Pisa!
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  20. chriscanaris writes: The preceding paragraph is also important: [...] Agreed. I think this ties in with my two questions above. In the paragraph you quote, Lean is making the case for what I identify as "question 1". In other words, "Yes, the sun plays an important role in climate, and there are a lot of things that climate models won't be able to get right without accounting for that!" chriscanaris continues with the disclaimer: This does not, repeat not, mean, 'Great, lets burn more coal folks!' Understood, and appreciated.
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  21. Ned: I think the migratory bird analogy is actually a very good one. I might take it further. Some birds get lost and end up in strange places. This probably means little in the scheme of things. When whole populations go off course, it probably means an awful lot. Which brings to mind John Cook's 'meme' of multiple converging lines of evidence one of which I think includes changing population distributions in various species. I'm going off topic but here, I have to confess to having a philosophical difficulty with the multiple converging lines of evidence notion - not because it lacks validity but because it's 'circumstantial' evidence. Of course, you can still get a jury to convict an offender if the circumstantial evidence is overwhelming. However, circumstantial evidence of its nature demands more rigorous testing. This rather than a wish to 'deny' AWG prompts the 'sceptical' undertone of many of my comments. Of course, I'd rather not see the temperature go up 6 degrees C in 2100. However, my wishing that it wouldn't won't alter the outcome if we have indeed messed up our planet (and continue to do so). So I maintain a keen interest in the debate watching how it plays out. A very recent interesting twist in all this seems to be that the Chinese in their usual 'subtle' approach to matters economic have reportedly just ordered a clamp down on greenhouse emissions - a big short term worry for Australia which has for better or worse hitched its economic wagon to Chinese demand for our coal and iron. It's said that the Chinese use the same character to represent 'crisis' and 'opportunity.' And apparently, one Chinese curse goes, 'May you live in interesting times!'
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  22. All the citations of Haigh are interesting... in that Haigh herself has said that it is disingenuous to claim that her work suggests recent warming has been caused by the Sun. Yes, the Sun has important impacts on climate. No, it isn't causing the recent warming.
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  23. chriscanaris: I know I make this comparison a lot, but climate change is very similar to plate tectonics in a lot of ways, one being the importance of "multiple converging lines of evidence." Both theories seek to explain very slow planetary-scale processes that can't be completely replicated in the lab and that aren't amenable to the traditional controlled-experiment that people in certain other fields get to use (there's only one Earth!). Thus, both theories rely on modeling, observational studies ... and multiple converging lines of evidence. We all accept plate tectonics (I hope), but some are reluctant to accept anthropogenic climate change. Of course, it's possible that in this case the particular lines of evidence for climate change are individually or collectively not as impressive as those for plate tectonics. Alternatively, one could speculate about other reasons that would explain people's willingness to accept one theory while rejecting the other, but I'd prefer not to wander that far off-topic. My point is just that we don't generally object to the reliance on "multiple lines of evidence" in principle, when it comes to complicated theories about planetary-scale physical processes.
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  24. It's said that the Chinese use the same character to represent 'crisis' and 'opportunity.' And apparently, one Chinese curse goes, 'May you live in interesting times!' The "crisis" and "opportunity" thing is a bit of a misunderstanding, at least as most Westerners use it. The words for "crisis" (wēijī) and "opportunity" (jīhuì) both incorporate the character "jī" but it doesn't really convey any sense of connection between the two. "Jī" is combined with lots of other characters to make bisyllabic words with all kinds of different meanings. Bringing this back within hailing distance of the topic of this site, Al Gore unfortunately repeated this fable about "crisis/opportunity" on a couple of occasions in speeches about climate change. For example, from his 2007 speech accepting the Nobel Prize:
    In the Kanji characters used in both Chinese and Japanese, "crisis" is written with two symbols, the first meaning "danger," the second "opportunity."
    So, chriscanaris, you've got good company on that one!
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  25. Thanks for clearing up an urban myth Ned (that's the crisis and opportunity one). As an interesting aside, there's a similar confusion around the Greek word 'stasis' which today we use to mean 'coming to a halt' but to the ancient Greeks meant a political crisis (no - I'm not showing off my non-existent erudition in classical Greek - my 21 year old son is the seriously bright Greek scholar who is now dipping into Mandarin!). Plate tectonics is fascinating. In Darwin's 'Voyage of the Beagle,' there's a fascinating description of major earthquake in South America - Darwin speaks of a big chunk of land rising. Darwin can't explain it but notes the phenomenon. I recall reading his description and having a huge 'Aha' moment - Darwin had just observed a shift which to a modern observer is all too obviously plate tectonics at work. So actually, the evidence for plate tectonics today is a little bit more than circumstantial. Indeed, we can measure its operation. Darwin's by contrast explained the phenomenon he observed in terms of volcanism (if my memory serves me correctly) citing the apparently near simultaneous eruption of a volcano some many (but not too many) miles away. In fact, of course, we recognise today that volcanic activity has heaps to do with plate tectonics. So Darwin proved was working on a good hunch - he just didn't know how to integrate the information because he didn't have all the bits of the jigsaw. I definitely don't reject evidence just because it's circumstantial - I merely argue for greater caution as would any defence barrister. But I don't hold a 'brief' for 'scepticism' even if my mind tends that way.
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  26. Ned @ 19 summed it up well. Yes, there are nuanced solar influences which can impact local temperature and weather, but the Sun is not responsible for the long-term increase in the average global temperature. It's important to distinguish between not understanding all solar effects and understanding the big solar effects. As for the format of the article, there's a reason I linked to the Intermediate version at the beginning. It has a very thorough list of peer-reviewed studies on the subject, and in fact that's primarily what it's devoted to. Thus it doesn't make sense to also devote the Advanced version to a long list of peer-review references. Instead I thought it would be a worthwhile endeavor to go through how the solar radiative forcing is calculated so that people can see the numbers for themselves. It's all well and good to read the IPCC's range of possible solar forcing values, but personally, I like to go through the calculations myself. And I think that's appropriate for an 'Advanced' rebuttal.
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  27. "solar magnetic field has not changed appreciably over the past three decades" By way of a partial update, see Solar wind loses power, which notes that "the sun's underlying magnetic field has weakened by more than 30% since the mid-1990s". The weaker solar (and hence interplanetary) magnetic field should mean higher incidence of galactic cosmic rays (GCRs) -- which matches observation. GCRs are the high-energy particles that should seed clouds and thereby cool the earth in the Svensmark model. However, we have persistent warming during this period. So weaker magnetic field = more GCRs and warming is indeed 'a nail in the coffin' for this idea.
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  28. One point to mention. Some astrophysicist are trying very ahrd to understand the interaction between the Sun and the Earth climate. This is why they are asking for grant and are paid. In consequence, they have no reason to dismiss the importance of greenhouse gases. Nevertheless, their studies indicate that the sun impact, while be real is not the cause of the actual climate change. By the way, the sun-climate relationship as been studied astronomers way before the impact of greenhouse gases was understood. Herschel speculated in 1801 that when the sun was highly spotted, it “may lead us to expect copious emission of heat and therefore mild seasons,” while few spots suggested “spare emission of heat” accompanied by “severe seasons”. In order to test his speculation that the observed changes on the sun might affect climate, Herschel turned to records of the price of wheat in England as a proxy for climate, because meteorological measurements were lacking. Herschel imagined that costly wheat would result from “severe seasons,” while the “mild seasons” would moderate the price of wheat. Herschel found in records of wheat prices support for his speculation—five lengthy periods of few sunspots were tied to costly wheat.
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  29. "Bond et al. (1999) added further evidence that the timing of D-O events disqualifies them from being responsible for the current warming, by showing that the most recent D-O event may have contributed to the Little Ice Age (LIA):..." I'm not a huge fan of this paragraph. Bond 1999 actually concludes
    "Finally, if we are correct that the 1-2 kyr cycle is a persistent feature of climate, at least in the North Atlantic, then one conclusion seems inescapable. Independent of any anthropogenic forcing, the North Atlantic's climate eventually will shift (or in fact may be shifting now) toward the warm phase of the cycle"
    Suggestions: 1) Several recent papers have challenged the idea that D-O events are related to a underlying periodic forcing (published post Rahmstorf 2003); e.g. 2) Even if a periodic component does exist (solar or otherwise), its magnitude must be so small as to render it nearly undetectable. Several authors (Rahmstorf, Alley, Ganopolski) argue for the use of stochastic resonance in modeling D-O events, whereby a very weak periodic forcing couples with strong noise to push the climate over a particular threshold in a glacial state. Something we have not observed to occur with much severity or regularity in the Holocene. -Robert S
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  30. I realize my #2 is oddly worded. I guess my brain got ahead of my fingers... 2) Even if a periodic component does exist (solar or otherwise), its magnitude must be so small as to render it nearly undetectable considering many "cycles" were missed altogether during the last glacial, and so-called Bond events are virtually nonexistent in the temperature record. Several authors (Rahmstorf, Alley, Ganopolski) argue for the use of stochastic resonance in modeling D-O events, whereby this very weak signal is greatly amplified by noise in the system to push the climate over a particular threshold in a glacial state.
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  31. "...published science is telling us "we don't know enough", yet the blog post boldly states "we know it isn't the sun". You mean like all the supporting published articles referenced in the article? C'mon
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  32. I'm no expert but I thought that Dansgaard-Oeschger events didn't make the whole globe hotter, they made the hemispheres go in opposite directions, one hotter, one cooler. And I didn't think it was so well established that the timing is always so regular; I thought that there was still substantial disagreement about it (from sensible people, not the wingnuts).
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  33. This was last my post for Muoncounter (unanswered)from "What caused early 20th century warming", which is directly relevant to this discussion: "In the absence of any anthropognic forcings prior to 1750AD, the only climate driver would be the various Solar cycles including the 11 year cycle, and multiple overlapping orbital cycles which have varied the Earth's exposure to the sun. Volcanic cooling is transient and significant in short bursts, but being randomly distributed in time cannot be counted as part of a natural forcing cycle. The Earth is most probably never in equilibrium, but if you are trying to separate and quantify the effects of CO2GHG forcing - you must be able to accurately tell us where we are in the cycle of 'natural' solar forcing." In new words: "What value of TSI gives the Earth neutral (neither warming or cooling) Solar forcing?" Perhaps Muoncounter could attempt an answer this time.
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  34. #33: "you must be able to accurately tell us where we are in the cycle of 'natural' solar forcing. Perhaps Muoncounter could attempt an answer this time. " Why? If you are questioning the content of this thread - that the observed warming is not due to the sun -- do so with specific objections. Or, as you suggest in the prior exchange, are you looking for a magic TSI number, so that you can claim that CO2 forcing is minimal? If so, that question is dealt with in specifics elsewhere. My comment here was about galactic cosmic ray flux, which was specifically a part of this post; I am happy to debate that subject in depth if you like.
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  35. Thanks for the good post, there's just one question left, I hope, it's not silly. You wrote dF = 0.7 * d(TSI)/4 This is a very straightforward and easy to understand formula - the larger the change in solar irradiance, the larger the energy imbalance it causes, and thus the larger the radiative forcing. Studies have reconstructed TSI over the past 300 years. Are there long term studies about the factor 0.7? Can we be sure, the albedo is a constant over centuries? For example, a change in cloud cover of about 2% can cause the same forcing as a doubling of CO2.
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  36. This is a good site and I feel the case for agw is very compelling, however I have one area of doubt regarding solar activity. Could the early 20th century largely solar forced warming be causing or contributing to the current warming by some delayed action or feedback? I cant see how it would and presume its been ruled out. Im not a scientist and it may be a naieve question. Id appreciate some clarification.
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  37. nigelj, your question is not naive! It is excellent and common. The answer is in the post Climate Time Lag.
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  38. I very much appreciate the chriscanaris/Ned exchanges. I wonder then if it's a matter of definitions, like with many other things. "The sun isn't causing global warming" means more "whatever the sun has been doing in the past few decades, global warming due to greenhouse gases has been there regardless" than (literally) "the sun is unable to cause global warming".
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  39. andreas - I'm not sure about the exact answer to your question, but notice that a 2% change in albedo would simply change the 0.7 to 0.68 or 0.72. In other words, it wouldn't change the solar forcing significantly.
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  40. omnologos - Yes, the sun is capable of causing climate change. However, all evidence available indicates that it is not the sole forcing responsible for the warming of the last 150 years (the magnitudes of solar change would require a huge climate sensitivity to those effects, and as no known solar changes correlate temporally), and that small solar variations are superimposed on the much larger CO2 driven warming.
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  41. omnologos writes: I very much appreciate the chriscanaris/Ned exchanges. So do I :-) I wonder then if it's a matter of definitions, like with many other things. "The sun isn't causing global warming" means more "whatever the sun has been doing in the past few decades, global warming due to greenhouse gases has been there regardless" than (literally) "the sun is unable to cause global warming". Yes, that's a nice summary of how I would describe it. Solar variation absolutely does have an effect on climate. It's just that in recent decades the sun has not varied by a whole lot [at timescales longer than the usual solar cycle], so its effect has been small.
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  42. dana1981 If I calculate a 1% increase in albedo and a constant TSI, I get dF = dA*TSI/4=2.4 W/m^2, comparable to the effect of CO2. Is constant albedo an assumption, the result of climate simulations or do we have measurements of it? Please don't misunderstand, I do not criticize your excellent post, only a (silly?) question.
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  43. The albedo effect and global warming (argument #90)
    The long term trend from albedo is that of cooling. In recent years, satellite measurements of albedo show little to no trend.
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  44. "The long term trend from albedo is that of cooling." That is not supported. For one thing there is no long term record (30+ years) of albedo. For another, the linear trend of the period of record actually shows a decreasing albedo (warming): Also, we have no basis of knowledge on what albedo was or how it varied before the age of satellites. Further, I have texts which put earth albedo at 29%, 30%, and 31%. The moon reflection people put it at 29% Guess what GISS AOGCM uses? 33% Our knowledge and use of earth albedo is obviously much less precisely known than the 1% cited by andreas.
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  45. andreas - the solar radiative forcing is proportional to the change in TSI. A constant TSI yields zero solar radiative forcing. The radiative forcing from albedo changes is a different question with a different formula, and one that I have not researched, so I can't answer that question.
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  46. Bibliovermis und ClimateWatcher Thanks for your help. Not so trivial and silly as I thougt. In the bibliovermis' link I found a lot of citations, where I can dig deeper. If I had knew, it's a sceptic argument, I had used the "search" field, sorry. But one thing, bibliovermis. The absolute value of albedo is not so important, it's the change, that's correlated to a forcing. And yes, Dana1981, you are right, my question was OT, it's another forcing, not solar.
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  47. andreas #42, ClimateWatcher #44 andreas - not a silly question at all. The Earth's warming imbalance from a combination of AG CO2GHG warming and cloud and direct albedo cooling is supposed to be +0.9W/sq.m. Your calculation of a 1% change in albedo (say 30 to 31%) makes a difference of 1366/4 x (0.70 -0.69) = 3.4W/sq.m. - much greater than the purported CO2GHG forcing of 1.66W/sq.m (IPCC AR4 Fig 2.4). What this does to GCM's which are cycled forward to predict in 2050 or 2100 is a very good question.
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  48. Ken Lambert #47 this calculations only takes not account the impact on incoming short wavelengths. As far as energy balance is concerned, the net effects is what matters.
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  49. argh, "first sentence should read "this calculations only takes into account ..."
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  50. Riccardo #48,49 Do you have a different number of W/sq.m for incoming solar than 239-240? Pray tell us what it is?
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