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This just in - the sun affects climate

Posted on 8 June 2009 by John Cook

A new Daily Tech blog post is propagating through the blogosphere, claiming a new NASA study attributes recent warming to the sun. The "new research report" is a NASA press release released in May 2008. The press release mentions that "fluctuations in the solar cycle impacts Earth's global temperature by about 0.1 degree Celsius, slightly hotter during solar maximum and cooler during solar minimum". This impact of the solar cycle on climate has been known for years.

Douglass 2004 calculates that due to the 1W/m2 change in Total Solar Irradiance (TSI) due to the solar cycle, you would theoretically expect a change in global temperature of 0.05°C. Instead, he observes a change of 0.1°C - he attributes the difference to positive feedback. White 1997 finds sea surface temperatures change by 0.1°C due to the 11 year solar cycle, looking at data from 1955 to 1994. Scafetta 2005 finds the 11 year solar cycle causes a change of 0.11°C in global temperatures going back to 1860. Camp 2007 found a signal of 0.18°C in global temperature attributable to the 11 year solar cycle.

However, the sun has shown little to no long term trend since the 1950's. This means that when modern global warming trend began in the 1970's, the correlation between sun and climate broke down. In fact, the long term trend for solar activity is that of cooling.  Not only is the sun not contributing to global warming, it has had a slight, long term cooling effect.

Figure 1: 11 year averages of Total Solar Irradiance (TSI, Max Planck Institute) and Global Temperature (GISS).

This break down in correlation is the reason why so much peer reviewed research investigating the link between sun and climate has concluded that the sun is not a major factor in global warming. Ammann 2007, Lockwood 2007, Foukal 2006, Scafetta 2006, Usoskin 2005 and many other papers (here is a more comprehensive list) all find the sun has had a minimal impact on global warming over the past 30 years.

Blaming global warming on the sun continues to be the #1 skeptic argument. When we gaze up into the huge, flaming ball in the sky (not for too long, I hope), it seems intuitive. How can you argue with such simple yet persuasive logic: "sun big, people small". I've even read one skeptic post comparing the size of the sun to the size of a CO2 molecule to hammer home the point.

However, focusing on one fact (the sun affects climate) while ignoring the broader picture (the sun is cooling) leads to the erroneous conclusion that the sun is causing global warming. Perhaps the only effective counter argument to "sun big, people small" is an equally simple argument: "earth warming, sun cooling".

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Comments 1 to 10:

  1. Contrarians have a tendency to not only recylce old arguments, but in this case to recycle old arguments and then distort them to support a political agenda. This is related to the same strawman that claims climate scientists think only CO2 affects climate. In NASA's 2007 temperature summary, Hansen notes: "This cyclic solar variability yields a climate forcing change of about 0.3 W/m2 between solar maxima and solar minima. (Although solar irradiance of an area perpendicular to the solar beam is about 1366 W/m2, the absorption of solar energy averaged over day and night and the Earth's surface is about 240 W/m2.) Several analyses have extracted empirical global temperature variations of amplitude about 0.1°C associated with the 10-11 year solar cycle, a magnitude consistent with climate model simulations, but this signal is difficult to disentangle from other causes of global temperature change, including unforced chaotic fluctuations. "
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  2. Then, there's this... New Paper Demonstrates Anthropogenic Contribution to Global Warming Overestimated, Solar Contribution Underestimated A new paper has been published in GRL by Scafetta and Willson entitled: ‘ACRIM-gap and TSI trend issue resolved using a surface magnetic flux TSI proxy model’ The Abstract states: “The ACRIM-gap (1989.5-1991.75) continuity dilemma for satellite TSI observations is resolved by bridging the satellite TSI monitoring gap between ACRIM1 and ACRIM2 results with TSI derived from Krivova et al.’s (2007) proxy model based on variations of the surface distribution of solar magnetic flux. ‘Mixed’ versions of ACRIM and PMOD TSI composites are constructed with their composites’ original values except for the ACRIM gap, where Krivova modeled TSI is used to connect ACRIM1 and ACRIM2 results. Both ‘mixed’ composites demonstrate a significant TSI increase of 0.033%/decade between the solar activity minima of 1986 and 1996, comparable to the 0.037% found in the ACRIM composite. The finding supports the contention of Willson (1997) that the ERBS/ERBE results are flawed by uncorrected degradation during the ACRIM gap and refutes the Nimbus7/ERB ACRIM gap adjustment Fröhlich and Lean (1998) employed in constructing the PMOD.” The authors state in their conclusions that: “This finding has evident repercussions for climate change and solar physics. Increasing TSI between 1980 and 2000 could have contributed significantly to global warming during the last three decades [Scafetta and West, 2007, 2008]. Current climate models [Intergovernmental Panel on Climate Change, 2007] have assumed that the TSI did not vary significantly during the last 30 years and have therefore underestimated the solar contribution and overestimated the anthropogenic contribution to global warming.” Scafetta N., R. C. Willson (2009), ACRIM-gap and TSI trend issue resolved using a surface magnetic flux TSI proxy model, Geophys. Res. Lett., 36, L05701, doi:10.1029/2008GL036307.
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    The ACRIM vs PMOD debate is a question over which composite of satellite TSI data is more accurate. ACRIM shows a slight warming trend. PMOD shows a slight cooling trend. Even using the ACRIM data, the warming trend is so slight, it is insufficient to explain the steep warming over the past 35 years. However, various independent measurements of solar activity all show closer agreement to the PMOD reconstruction which indicates the sun has been showing a cooling trend over the last few decades. This is explained in detail at Determining the long term solar trend.

    UPDATE: I read the Scafetta paper which claims the ACRIM data (which shows slight warming) is more accurate than the PMOD data (slight cooling) because it shows closer agreement with the TSI reconstruction by Krivova and Solanki. I found this curious as Krivova 2007 itself compares its results to PMOD and finds close agreement. So I contacted Sami Solanki, one of the authors of the Krivova model. He replied (very promptly, a very approachable scientist) that they had actually written a paper responding to Scafetta's claims that is currently awaiting publication. I will keep everyone posted when the paper is published.

    Incidentally, Krivova's TSI reconstruction is the data I use in Figure 1 above.

    UPDATE 2 Nov 2009: The response from Solanki and Krivova has been published. I summarise it's findings in ACRIM vs PMOD, the rematch.

  3. You haven't addressed lag-time effects with your sun-temperature disconnect theory from about 1980. Tying in effects on clouds, or the earths magnetic field (which has been declining naturally for the last few hundred years-which would amplify any warming-an important point), and you could explain a global emperature peak around 2002. For example: -When is the hottest part of the day?-around 3 hours AFTER the sun reaches its peak (~30% of the entire day-warming trend). -Which is the hottest part of the year?-about 6 weeks AFTER the longest day of the year (~25% of the annual warming trend). If 25-30% heat lag effects are a guide, then adding 25-30% of lag time to the suns warming trend, from a peak around 1980 fits perfectly with a peak around 2002. To pre-empt a reply based on the lag time only, don't forget, there may be OTHER factors that enhance lag time, such as the very slow lag-time heating of the ocean, the earth's magnetic field reduction, and clouds etc etc. Please address? It is one of the biggest arguemnts of skepics, but I don find your site addressing it much anywhere.
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    Response: The issue of climate time lag is addressed in the post coincidentally titled Climate Time Lag.
  4. Thingadonta, you seem to think you have a model of climate with which you can attribute portions of temperature change to specific causes. And you think that yours is better than models used for such purposes by "all the PhDs" who contribute to climate science via research articles used by the IPCC. Rather than making an anonymous assertion that can't be scrutinized by others, please show us the model. "It is one of the biggest arguemnts of skepics [#6]" -- perhaps the model is already published? If not, then maybe you can convince a skeptic luminary to help you formalize it? That would be excellent, because then the model could be used to make predictions. I gather from what you've written that you expect temperature to decrease into the future. How much future warming will be inconsistent with your model? PS. Can you cite a peer-reviewed scientific publication describing the effect of Earth's magnetic field on average surface temperatures?
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  5. The earths magnetic field has been declining for several hundred years, and some are worried that it might actually flip soon (we will see compass's needles pointing south, instead of north-this is common in geological time, and has been used to correlate, in time, magnetic-bearing rock sequences which show identical flip patterns over time. I think, from memory, magnetic flips occur roughly every several hundred thousand years, (but don't quote me on this) and,to use a bad cliche, "we are due"). Anyway, I read in some internet sites that a lower magnetic field suggests an increased solar effect, it is mentioned in eg the meeting between Minister Wong and Fielding and Co. scientists, but I dont have any papers per say, on hand. Try the NIPCC 'climate reconsidered' report which is a good overview of alternative theories, also Plimers recent book may contain reference footnotes on it.
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  6. "Link between the earth's magnetic field and low-latitude precipitation? Mads faurschou knudsen and Peter Riisager, Department of Earth Sciences, University of Oxford, Parks Road, Oxford OX1 3PR, UK. Pages 71-74. Based on an observed correlation between the Earth's magnetic dipole moment and oxygen isotope paleo-precipitation records from caves in Oman and southern China, knudsen and Riisager suggest that the Earth's magnetic field may have influenced the amount of rainfall in low-latitude regions during the past 5000 years. The physical mechanism that underpins the geomagnetic-climate link is provided by the cosmic-ray-climate theory, which suggests that galactic cosmic ray (GCR) particles entering the atmosphere influence the formation of low-altitude clouds and, in turn, climate. The geomagnetic field shields the Earth from GCR particles and, according to the cosmic-ray-climate theory, it therefore has the potential to influence cloud formation, rainfall, and climate. Since the amount of GCR particles entering the atmosphere is also modulated by the Sun, the cosmic-ray-climate theory is central to the ongoing scientific debate regarding the role of the Sun in climate change. knudsen and Riisager lend support to the notion that variations in the Earth's magnetic field may influence the climate of our planet. They also deliver independent support for certain aspects of the cosmic-ray-climate theory." There are other sites giving an over-view of this research. In addition there is the ongoing debate over magnetic field/cosmic rays/cloud initiation as posted in "Do cosmic rays cause clouds?" thread.....see
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  7. Regarding the TSI/Global graph above: To me it appears there would be much more correlation between the two variables if you shift the TSI measurments slightly to the left to compensate for the delay between the sun's activity and the resulting Earth temperature. While there seems to be a disconnect starting at about 1980, the final plots seem to have more harmony, however the overall disparity is greater. Comment?
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  8. The corelation is with the inyterplanetary field/ ionising cosmic radiation and cloud (the best fit of cosgenic isotopes with temperature being with a 10 year lag). The magnetic field peaked in the mid to late 80's, clouds cover was a minumum around the turn of the century. This is 2009 - no increase in surface temp for a decade, no increase in sea level (and therfore temp) in years and a substantial increase in albedo over a decade. A sin by omission several times over.
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    Response: Actually, there has been no correlation between cosmic rays and global temperatures over the last 30 years of global warming. Measurements of the climate's total heat content find the planet has continued to accumulate heat since 1998. And sea level rise has been accelerating over the last century and is still rising.
  9. >>>>UPDATE: I read the Scafetta paper which claims the ACRIM data (which shows slight warming) is more accurate than the PMOD data (slight cooling) because it shows closer agreement with the TSI reconstruction by Krivova and Solanki. I found this curious as Krivova 2007 itself compares its results to PMOD and finds close agreement. So I contacted Sami Solanki, one of the authors of the Krivova model. He replied (very promptly, a very approachable scientist) that they had actually written a paper responding to Scafetta's claims that is currently awaiting publication. I will keep everyone posted when the paper is published.<<<< Hi, I just registered, although I've been reading here for a while trying to educate myself. Thanks for putting together such a useful, easily navigable and attractive resource. I particularly like how the relevant scientific papers are provided and linked. I was wondering if there had been any updates on this, specifically Solanki's response, but generally any refutation or critical discussion about the Scafetta/Willson 2009 paper?
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    Response: The response from Solanki and Krivova has been published. I summarise it's findings in ACRIM vs PMOD, the rematch.
  10. Hi John - not sure whether you've seen this or not... "Scientists find errors in hypothesis linking solar flares to global temperature" "The theory of anthropogenic global warming consists of a set of logically interconnected and consistent hypotheses,” Martin Rypdal said. “This means that if a cornerstone hypothesis is proven to be false, the entire theory fails. A corresponding theory of global warming of solar origin does not exist. What does exist is a set of disconnected, mutually inconsistent, ad hoc hypotheses. If one of these is proven to be false, the typical proponent of solar warming will pull another ad hoc hypothesis out of the hat. This has been the strategy of Scafetta and West over the years, and we have no illusion that our paper will put them to silence. However, the only scientifically valid strategy to confront these new hypotheses is to shoot down every new missile as they come in, using the most advanced weapons at hand. We believe that this operation was successfully accomplished with respect to the complexity linking hypothesis, but there will be many more battles to be fought until the issue of the contribution of solar variability to recent global warming is settled.”
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