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It's the sun
Climate's changed before
There is no consensus
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Solar activity & climate: is the sun causing global warming?

The skeptic argument...

Temp and Solar Activity In 2005, the BBC reported the sun was more active over the past 60 years than anytime in the previous 1150 years. Over the past few hundred years, there has been a steady increase in the numbers of sunspots, just at the time when the Earth has been getting warmer. The data suggests changing solar activity is influencing in some way the global climate causing the world to get warmer (Source: Sunspots reaching 1000-year high by David Whitehouse, Graph: The Great Global Warming Swindle by Martin Durkin)

What the science says...

As supplier of almost all the energy in Earth's climate, the sun certainly has a strong influence on climate change. Consequently there have been many studies examining the link between solar variations and global temperatures.

The correlation between solar activity and temperature

The most commonly cited study by skeptics is a study by scientists from Finland and Germany that finds the sun has been more active in the last 60 years than anytime in the past 1150 years (Usoskin 2005). They also found temperatures closely correlate to solar activity.

However, a crucial finding was the correlation between solar activity and temperature ended around 1975. At that point, temperatures rose while solar activity stayed level. This led them to conclude "during these last 30 years the solar total irradiance, solar UV irradiance and cosmic ray flux has not shown any significant secular trend, so that at least this most recent warming episode must have another source."

You read that right. The study most quoted by skeptics actually concluded the sun can't be causing global warming. Ironically, it's the sun's close correlation with Earth's temperature that proves it has little to do with the last 30 years of global warming.

Measurements of solar activity

This is confirmed by direct satellite measurements that find no rising trend since 1978, sunspot numbers which have leveled out since 1950, the Max Planck Institute reconstruction that shows irradience has been steady since 1950 and solar radio flux or flare activity which shows no rising trend over the past 30 years.

Other studies on solar influence on climate

This conclusion is confirmed by many studies quantifying the amount of solar influence in recent global warming:

  • Ammann 2007: "Although solar and volcanic effects appear to dominate most of the slow climate variations within the past thousand years, the impacts of greenhouse gases have dominated since the second half of the last century."
  • Lockwood 2007 concludes "the observed rapid rise in global mean temperatures seen after 1985 cannot be ascribed to solar variability, whichever of the mechanism is invoked and no matter how much the solar variation is amplified."
  • Foukal 2006 concludes "The variations measured from spacecraft since 1978 are too small to have contributed appreciably to accelerated global warming over the past 30 years."
  • Scafetta 2006 says "since 1975 global warming has occurred much faster than could be reasonably expected from the sun alone."
  • Usoskin 2005 conclude "during these last 30 years the solar total irradiance, solar UV irradiance and cosmic ray flux has not shown any significant secular trend, so that at least this most recent warming episode must have another source."
  • Haigh 2003 says "Observational data suggest that the Sun has influenced temperatures on decadal, centennial and millennial time-scales, but radiative forcing considerations and the results of energy-balance models and general circulation models suggest that the warming during the latter part of the 20th century cannot be ascribed entirely to solar effects."
  • Stott 2003 increased climate model sensitivity to solar forcing and still found "most warming over the last 50 yr is likely to have been caused by increases in greenhouse gases."
  • Solanki 2003 concludes "the Sun has contributed less than 30% of the global warming since 1970".
  • Lean 1999 concludes "it is unlikely that Sun–climate relationships can account for much of the warming since 1970".
  • Waple 1999 finds "little evidence to suggest that changes in irradiance are having a large impact on the current warming trend."
  • Frolich 1998 concludes "solar radiative output trends contributed little of the 0.2°C increase in the global mean surface temperature in the past decade"

Ocean Thermal Inertia

Solanki also found that over 1150 years, temperature lagged solar activity by 10 years. Eg - presumably due to ocean thermal inertia, it took Earth's climate 10 years to catch up to changes in solar activity. This is exactly what's observed in the 20th century - in the early decades, solar activity rose sharply with temperature lagging a decade behind. When solar activity leveled out in the 40's, so too did global temperatures.

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Related Arguments

  1. "From the actual data we conclude that the graphs from Lockwood and Frölish were flawed:

    1. The methodology used by Lockwood and Frölish to smooth the lines was applied only to maxima of R (sunspot number), dismissing the TSI. This practice hides the minima, which for the issue are more important than the maxima. For example, if the minimum of TSI in 1975 was 1365.5 W/m^2, it would contrast dramatically with the minimum of TSI of 1998 that was 1366 W/m^2 (0.033% higher). That would make the Sun in 1975 “colder” than in 1998. However, if we compare minimum values with maximum values, then the Sun would be frankly “warmer” in 1998 -when the solar energy output was 1366 W/m^2- than in 1975 -when the energy output was 1366.1111 W/m^2. Today (21/07/07), the global TSI was 1367.6744 W/m^2); hence, we see that we must not smooth maxima values through movable trends because we would be hiding the minima values, which are more important because the baseline of the “cooler” or lower nuclear activity of the Sun are higher everyday. The coolest period of the Sun happened during the Maunder Minimum when the TSI was 1363.5 W/m^2. The coolest period of the Sun from 1985 to date occurred in 1996 when the TSI was 1365.6211 W/m^2. An interesting blotch is that in 1985 the TSI was 1365.6506 W/m^2 and in 2000 was 1366.6744."
  2. The Lockwood article does not mention the methodology that the author of that page, Nasif Nahle, claims the researchers have used. The main critique towards the Lockwood article should be the fact that it used only 30 years of data to make the claim that the total solar irradiance (TSI) has decreased since 1985. Not only does it fails to mention that the trend found is hardly significant, it also neglects to show any TSI data (derived or not) before the year 1975.

    All of this is irrelevant however, as the alternative reconstruction of solar irradiance that Nahle presents, also indicates no trend after 1950. Strangely though according to Nahle the graph should show that there is a clear increase in solar irradiance, but perhaps we are seeing different things? To me, clearly, there is no significant trend in TSI visible from 1950 onwards.

    It is clear just by looking with the naked eye but also by using the provided data, applying a 11-year low-pass filter (to eliminate the variance of the ~11-year sunspot cycle) and calculating the first derivative of this filtered series. The trend over the last 30 years of the series, 1971-2000, has been roughly +0,08 W/m² and is not significant (at all).

    Figure: solar irradiance from Lean (2000), blue: raw data, red: 11-year low-pass filter
  3. Just assuming for the sake of argument that your assertions based upon

    are proven by peer-reviewed studies to be correct and that: -

    Recent oppositely directed trends in solar climate forcings and the global mean surface

    is shown by peer-reviewed studies to be wrong in some way, that still does not invalidate the
    fact that Solar output [once the 11-year cycle has been removed], has had no tend or virtually no trend.

    Claims that the recent anomalous warming are solely due to solar effects are unsustainable. It is clear that the current anomalos warming cannot be explained without including the effects of GHGs and CO2 in particular.
  4. I think I have the right to argue on my article based on peer reviewed papers.

    When we consider a short period, for example an 11 years period we can argue that the intensity of the solar irradiance is decreasing; however, if we consider a longer period, for example 400 years, we can see that the intensity of solar irradiance has not decreased. Some 400 years ago the solar irradiance intensity was 1365.5946 W/m^-2, while in 2000 the total solar irradiance intensity was 1366.6620 W/m^2. This year the Sun has been mostly spotless, but the solar irradiance intensity has been 1365 W/m^-2. This constitutes evidence on the existence of other solar "pulses" that we have not understood well:

    Regarding the particularity of CO2 on the global warming, I don't see why to blame the CO2 of GW when its particular thermal characteristics show that the CO2 is not capable of producing any warming. The Pp of the CO2 in the atmosphere is roughly 0.00034 atm*m, wich limits the absorptivity-emissivity of the CO2 to only 0.00092 (dimensionless value), not the 0.2 given by the IPCC. The absorptivity-emissivity of CO2 is 0.00092 conduces to its total emittancy of barely 0.414 W/m^2, not the 5.35 W/m^2 given by the IPCC. If I was to blame any atmospheric gas of a GH effect, I would blame the Water Vapor, not the the coolant CO2.
  5. Biocab: surely you can agree with the consensus that solar irradiance has not increased significantly in the last 50 years, while the global average temperature has? The only conclusion can be that changes in solar irradiance cannot have contributed to recent warming in the last half century.

    With regard to CO2: I think you are not completely aware of the exact concept of the natural greenhouse effect, the enhanced greenhouse effect and most important of all radiative forcing. I am not an expert on the exact chemistry of all the trace gases and how that works, so I cannot judge your comments on the exact emissivity (though my gut feeling hints at the missing of the immediate re-emittance of longwave IR-radiation while you seem to be talking only about the independent emittance of the absorbed heat). I do know the following though: the absolute value of carbon dioxide (whether expressed in ppm or Pp) is not relevant when it comes to the increase or decrease of the Earth's surface temperature. Changes in the exact amount of each gas are what is important. The reason for this is that such changes will cause changes in radiative fluxes and, as a part of the total atmospheric adjustment for these radiative inbalances, the earth's surface cools or warms. Now given that carbon dioxide concentrations have risen at least 35% since 1900, there surely must have been some warming due to carbon dioxide (though not due to the existance of the gas in the first place, but because of the increase in its concentration).

    I am more at home in meteorology, so some rough calculations about that: the upward surface flux of the earth is around 390 W/m² (sigma T^4 = 5,6704x10^-8 * 288^4 ~ 390) and the outward flux at the top of the atmosphere is (1-a)S/4 where a ~ 0.3 (the global, terrestial albedo of the atmosphere) so this flux comes down to about 240 W/m². Now you can easily see that a large amount of longwave radiation must have been absorbed by the atmosphere, roughly 150 W/m². We know that water vapour is by far the primary absorber and carbon dioxide relatively weak (that is what you have showed, I think). Then comes radiative forcing: this can be understood simply by looking at toy models, which show that if the solar input or emissivity of the earth or the atmosphere (e.g. the greenhouse gasses) changes, the Earth's surface temperature changes.

    To conclude, models have shown that a doubling in CO2 concentration will likely cause a radiative forcing of around 3,7 W/m². One can now find that the coefficient for determining the radiative forcing caused by an increase or decrease of CO2 concentration from any given value A to B, will be C = 3.7 / ln(2) = 5.34 (and reversing the equation results in DF = 5.34 ln(co2/co2_orig) ). I am just a layman but I am pretty sure the value you quoted, 5.35, is NOT the total emissivity of carbon dioxide but only a coefficient effectively indicating the climate sensitivity to CO2 doubling. The value is not even in W/m² but dimensionless.

    Note of caution: I consider myself a layman and excuse me for any dramatic failures in reasoning. Willing to learn though :).

  6. 5.35 needs to have units:

    delta T = W/m^2 [Ln (ppmv/ppmv)] / 4 (W/m^2*K^4) (K^3)

    If don't, how could we eliminate W/m^2 from Stephan-Boltzmann constant?
  7. I don't agree with consensus, I agree with science.

    In the last 50 years the Intensity of Solar Irradiance increased in 1981 uo to 1366.6829 W/m^2. Higher than in 1957 (1365.7689 W/m^2); consequently, in 1981 was higher than 50 years ago. In 2000 the ISI was 1366.6620 W/m^2, and it was higher than 50 years ago (ISI in 1957 was 1365.7689 W/m^2). The last year (2006) the ISI was 1367.25 W/m^2, higher than in 1957, 1981 and 2000. Is ISI increasing or decreasing in the last 50 years?

    The inciding IR upon the surface is not 240 W/m^2, but ~469 W/m^2. From the last load of energy, the surface absorbs ~356.15 W/m^2 (median ~342 W/m^2) (1- Manrique, José Ángel V. Transferencia de Calor. 2002. Oxford University Press. England. 2- Maoz, Dan. Astrophysics. 2007. Princeton University Press. Princeton, New Jersey

    Some scientists from the IPCC think that the value 5.35 W/m^2 is wrong... I agree:
  8. An increase of 1365,7689 to 1366,6620 is not in any way statistical significant. Pick two others years and you get a decrease (e.g. what Lockwood did). You did not account for the 11-year periodic cycle which needs to be substracted before looking at trends, which underlines the uselessness of randomly picking TSI from any given year or years. Ergo: looking at the data with the 11-year cycle substracted, the trend in the last 50 years is more or less neutral (+0,08 W/m²) and in any case not statistical significant, given the amount of variance in that same period.

    Inciding IR upon the Earths surface is not ~240 W/m², sure I agree with that, but then again I am not claiming it is (I said it was the outgoing flux at the TOA). The ~469 W/m² is the [total] incoming IR at the surface, which is a combination of solar flux and radiation coming from the GHGs (water vapour, carbon dioxide, so on). IPCC puts it at 492 W/m² as a consensus though. Of that amount about 452 W/m² goes into the atmosphere by latent heat exchange, evapo(trans)piration and absorption by GHGs (the latter roughly 350 W/m²). The atmosphere itself radiates 195 W/m² upwards into space and 324 W/m² downwards towards the surface. About 40 W/m² makes it directly from the Earth's surface into space. The incoming solar flux is ~235 W/m² (and outgoing as well), of which 67 W/m² is absorbed by the atmosphere and 168 W/m² reaches the surface. So summarizing: the [surface] incoming flux is ~492 W/m² and outgoing as well, the TOA incoming and outgoing flux is ~235 W/m². The atmosphere absorbs 519 W/m², most of it from below from the Earth's surface, and emits this upwards and downwards (mostly the latter). As far as I can tell, nothing of this appears in real contradication with your article from Manrique (2007).

    The 5.34/5.35 is indeed in W/m², I stand corrected. The ln(co2/co2_orig) only scales the value and deltaF is in W/m².

  9. Well, let's compare 1957 (50 years ago) with 2006 (one year ago). In 1957 the ISI was 1365.7689 W/m^2, while in 2006 the ISI was 1367.25 W/m^2. Where is the decrease?

    The radiative forcing from ISI is 0.85 K per each W/m^2 of solar IR. From 1957 the extent of ISI has been 1.4811 W/m^2, that is 1.26 K. It is more credible than the 0.02 K from the heat absorbed by the CO2.

    The point where I don't agree with you is the radiative forcing for CO2, which is not 5.35 W/m^2, but 0.414 W/m^2. That was considered in the NAS paper. It seems, from the article, that the value for deltaF wasarbitrarly fixed.
  10. What is your source of 1367,25 W/m² for 2006, honestly for me it would seem like an unrealistic jump from the late 1990's to now. According to the PMOD-WRC data (link above, 'direct satellite measurements'), which is consistent with Lean (2000), the average TSI last year was 1365,4 or 1365,5 W/m² which seems more appropriate than 1367 W/m². In any case you cannot directly compare 1957 with 2006 because 2006 was the 11-year cycle minimum and 1957 was a cycle maximum, so compare maxima or minima or averages per solar cycle instead. E.g. if I use the Lean (2000) data from your webpage and compare 1957 with 2000 (maximum of solar cycles 19 and 23), I get 1366,681 and 1366,724, which equates to deltaF = 0,043 W/m² or a deltaT of 0,06 according to your equation. The first half of the century however I see a deltaF of 1,6 W/m² in the maxima and deltaF of 1,0 W/m² in the minima, equating to deltaT = 1,6-2,4 degrees. This strikes me more as a debate on data than principals or methods, by the way.

    The detrended data shows no [significant] decrease or increase in TSI/ISI. From that perspective I neither agree with the Lockwood article that ISI has decreased in the last 25 years nor with the claim that it has increased in the last 50 years. I would have to make myself more familiar with the exact fundamentals of radiative forcing before investigating whether or not the trend found would induce any (significant) forcing, your equation looks nice but I want to check it for myself first :-). On CO2 forcing: climate sensitivity to doubling of its concentration has a probability range even in the IPCC reports, however further discussion on this is not meant for this page.
  11. Small addition: this is what you get when you compare random years, say 1966 and 1996 (thirty years): 1365,951 and 1365,621, a decrease of -0,330 W/m². This is all using the Lean (2000) data from your webpage. Now 1966 was three years away from the maximum of cycle 20 in 1969 and 1996 was the minimum at the end of cycle 22.
  12. Philippe Chantreau at 03:00 AM on 21 September, 2007
    I like your analysis Ben. If you haven't, check Tamino's post "PMOD vs ACRIM." He did an outstanding job of examining solar data. Hope John isn't going to get tired of me always referring to other sites!
    [ Response: Not at all - the point of Skeptical Science is to point people to relevant resources, primarily the peer reviewed papers but good blog posts too. Tamino has two great posts which I link to from my Is the sun getting hotter? page (and I even lifted one of his graphs to use on my page). ]
  13. Ben Lankamp, the source is

    It's not unrealistic given that the data is NH instrumental. Solar irradiance is going up, not down. You cannot take just one sunspots cycle out of context. The last would be pseusoscience.
    [ Response: The only information at the LASP page about long term trends in solar irradiance is the following graph:

    What it shows is a close correlation between Solar Irradiance (the orange line) and global temperature (dotted blue line). But they also show the correlation ends when the modern global warming trend begins in the mid-70's. The data is all there and it's unambiguous - there's a reason why so many studies (listed above under "Other Studies on solar influence on climate") conclude the sun's influence on recent global warming is minimal. ]
  14. No, what it shows is that the solar irradiance in 2006 was 1367.25 W/m^2.
  15. Philippe Chantreau at 11:49 AM on 25 September, 2007
    What it also shows for the 20th century is that the timing is not quite right. Temp increases sharply before the TSI and then, even before the TSI reaches its first 20th century spike, the temp actually starts to decrease, followed by a TSI decrease, and then the temp increases again, followed again (very modestly) by the TSI. If I was using a skeptical aproach to attempt a correlation between the 2 on this graph, it would appear that TSI was driven by temperature during the 20th century.
  16. I notice John, that you have done some renovating. Where did your last thirty years of satellite measurements of the TSI disappear to?
    To the unpracticed eye nothing out of the ordinary is apparent, but to people familiar with the site, it looks as though you are erasing key information that supports Biocab's contention that in regard to TSI it is the minimum measurement extended over time that is the most important. And the minimum is trending up - or rather was. If the current lack of sunspots extends a while longer, and the next solar cycle sees a drop in overall activity followed by a drop in global temperature, will you become a co2 denier?
    What about you Phil?
    [ Response: Not sure what you're refering to but I haven't removed anything (I am constantly tweaking the site but it's mostly adding links to new studies as I encounter them). Perhaps you were thinking of the discussion of satellite TSI data at The sun is getting hotter. As for the next solar cycle and the prospect of a drop in global temperature, it's funny you should mention that - I'm working up a page on that very subject which I'll post later this week. ]

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