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Who was it that said that the good thing about science was that you get such a lot of speculation from such a small number of facts? The recent paper by Haigh et al concerning measurements of the solar spectrum is an excellent example.

This interesting paper and what it actually said has been lost amongst the comments made about it in an associated press release and interviews, about which more later.  It’s obvious that many of those who reported on the papers findings have only read the press release. But then looking a little deeper only confuses things.

The instrument used to make the observations was the Spectral Irradiance Monitor (SIM) onboard the SORCE satellite. The SIM is of a design that hasn’t flown in space before. It looks at the total radiation from the sun in the visible and Infra-Red bands, and produces a spectrum of the sun usually twice a day. It’s been in space since 2003.

Its raison d’être was that whilst it is known that the total solar irradiance changes slightly over the 11-year solar cycle, it has only been suspected and shown relatively recently that the shape of the solar spectrum changes over the cycle. Judith Lean of the US Naval Research Laboratory showed in 2000 that the solar Ultra-Violet radiation varies by a factor of ten greater than the visible in a way that is out of phase with the sun’s visible radiation.

The question is how this affects the earth’s atmosphere and climate. The general feeling among many, though not all, solar scientists that solar irradiance changes can account for about 0.1 deg C of the approx 0.4 deg C global rise in temperature over the past 30 years. However, given the large UV variability some suggested that it may have a larger effect perhaps due to some unknown amplification effect in the atmosphere.

As an aside, there is some research that attributes the changing solar irradiance a greater influence, Camp and Tung (2007) writing in Geophysical Research Letters conclude that the temperature increase is 0.2 deg C.

Changing Sun

So the SIM swung into action. The new paper by Joanna Haigh et al is based on two datapoints, or rather two spectra. They are 10-day averages centred around 21 April 2004 and 7 November 2007, when the solar cycle was in its declining phase from the 2000 peak. Haigh et al find that the sun’s spectrum was different on the two dates. There was a larger decline in Ultra Violet radiation than expected. Visible radiation increased almost compensating.

At first sight it is not surprising that there should be differences considering the very different state of the sun on those two dates. In April 2004 the sun was halfway down from its peak activity (several flares were recorded during the observation period) with a monthly sunspot count of about 40 (at the peak it was about 120). In November 2007 however the monthly sunspot number was about 2, which is just about as low as it gets, (for example in the previous cycle there were only two months that low, and in the cycle before that just one.)

Take a look at Soho observations of the sun on the two dates. You can see the numerous active regions in 2004, whilst in 2007 there are hardly any. Click on image to enlarge.



This leads one to wonder what the differences in the spectrum mean and where they came from and could they be related to changes occurring as part of the solar cycle or just as a result of shorter-term fluctuations? Two datapoints from such a variable sun is clearly inadequate to determine very much. What for example is the difference in solar spectra between an active sun and a lesser active sun during the same year? How does the spectrum vary at solar minimum, if at all? Also we know that the sun is currently behaving strangely these days.

When plugged into atmospheric models the researchers found that using the 2007 data when the Ultra-Violet had decreased there was an increase in visible radiation reaching the lower atmosphere. It caused a warming. One should note that the Hadcrut3 global data set shows that the Earth’s temperature was unchanged between 2004 and 2007. This means that, if we accept the researchers conclusions, some other cooling factor (or combination) must have compensated exactly for the sun’s warming influence resulting in no observable change in the Earth’s temperature!

Reverse Logic

Then the authors SPECULATE that the reverse MIGHT be true, that is that if the visible radiation decreases at solar maximum then the earth might cool.

Based on this speculation, not in the Nature paper but elsewhere, the authors suggest that as solar activity increased throughout the 20th century the sun may have been a cooling influence.

Consider what was actually said in the Nature paper.

“At present there is no evidence to ascertain whether this behaviour has occurred before, but if this were the case during previous multi-decadal periods of low solar activity it would be necessary to revisit assessments of the solar influence on climate and to revise the methods whereby these are represented in global models.”

In associated press release the lead author is quoted as saying, “We cannot jump to any conclusions based on what we have found during this comparatively short period and we need to carry out further studies to explore the sun’s activity and the patterns that we have uncovered on longer timescales.”

One could paraphrase the situation by stating that one should be very cautious about these observations themselves and the fact that there are only two datapoints and because they are anomalous. So while they cannot “jump to any conclusions” that’s nonetheless exactly what they are going to do.

Here it all starts to unravel. In recent years many scientists have made set great store by what they claim is the fact that their climate models (which include solar influences) can completely explain what was going on in the climate up to about 1960 without mankind’s influence, but that after 1960 manmade global warming is necessary to explain the data. It was this line of argument that an initially skeptical David Attenborough said persuaded him of mankind’s influence.

Now if Haigh et al are right the solar factor in this climate modeling was incorrect even though it did an amazing job of reproducing natural variations in climate from the 19th century up to 1960! So, one wonders, which is wrong, the suggestions by Haigh et al, or the climate models that reproduced natural variability so well up to 1960 (suspiciously well, in my view).

I’m also wondering how this research fits in with the infamous Lockwood and Frolich Royal Society paper of 2007. That used sunspot data and GISS global temperature data to show that as the sun’s activity declined after the great solar grand maxima of the late 20th century the earth’s temperature continued to rise. They concluded that the sun’s increased activity wasn’t responsible for the world warming (had they used another global temperature dataset I think they might have got a different answer.) If Haigh et al are right then the decline in solar activity, estimated by Lockwood and Frolich to be in the 1950’s (it was also in the 80’s) actually coincides with the recent spell of warming! So one could now argue it was the sun that did it after all!

Then there are the Maunder and Dalton minima. These are periods of low solar activity that coincided with cool global temperatures. If Haigh et al are correct then the quiet sun, rather than cooling the planet, would have been warming it. The impression I get is that climate models struggle to explain these cooling episodes. The Maunder Minimum requires low solar activity and volcanic effects according to one explanation. If Haigh et al get their way then that explanation fails utterly.

The Wrong Message

Another aspect of the paper was the way it was presented to the media with the researchers stressing that the possibility that we may have misunderstood the sun’s influence on the Earth, not just by magnitude by reversed in direction as well, offers no support for any skeptical view of climate change influences.

The logic is that despite our postulated ignorance of solar influences in the past, the new correction confirms the view that the sun is still a minor player because the sun exerts a cooling influence at times when the earth’s global temperature was increasing, so the other factors, including mankind, must be far greater. Perhaps the fact that so many in the media have taken the view that it this research supports doubt about current understanding is the mixed message that scientists were completely wrong about the sun (set against the backdrop of professed certainty in the past), along with the coda that we shouldn’t worry as it doesn’t really make any difference!

The sun is making a comeback. Look at articles in the leading journals as well as press reports of 15 years ago and it was not uncommon to see scientists saying that the sun was an important influence in climate change. About a decade ago that changed, but in recent years it has been coming back in many ways.

And still the sun remains historically quiet, greenhouse gasses accumulate in the atmosphere, and the annual global temperature refuses to increase.