Monday, November 12, 2007

Why it was the European Warm Period
and the Very Little Ice Age


Recently, Eli got tangled in a toodo at Tamino's (where are the bouncers when you need them) with one Leif Svalgaard, who looks at solar insolation for a living. Eli played but a small role in the proceeding. To make the story very short (and indeed it went on more and more and more and almost lead the mild mannered T to close up the comments)

Svalgaard propounds (go read Tamino) that there is no difference in solar insolation between solar cycle minima extending back to the year dot, and the year dot includes our beloved Maunder minima. Eli went and RTF AR4 on this, and indeed the solar gang has changed its tune, not as far as Svalgaard, but certainly a major change from the TAR.

The magnitude of the long-term trend in solar irradiance remains uncertain. A reassessment of the stellar data (Hall and Lockwood, 2004) has been unable to confirm or refute the analysis by Baliunas and Jastrow (1990) that implied significant long-term solar irradiance changes, and also underpinned some of the earlier reconstructions (see Section 2.7). Several new studies (Lean et al., 2002; Foster, 2004; Foukal et al., 2004; Y.M. Wang et al., 2005) suggest that long-term irradiance changes were notably less than in earlier reconstructions (Hoyt and Schatten, 1993; Lean et al., 1995; Lockwood and Stamper, 1999; Bard et al., 2000; Fligge and Solanki, 2000; Lean, 2000) that were employed in a number of TAR climate change simulations and in many of the simulations shown in Figure 6.13d.

In the previous reconstructions, the 17th-century ‘Maunder Minimum’ total irradiance was 0.15 to 0.65% (irradiance change about 2.0 to 8.7 W/m^2; radiative forcing about 0.36 to 1.55 W/m^2) below the present-day mean (Figure 6.13b). Most of the recent studies (with the exception of Solanki and Krivova, 2003) calculate a reduction of only around 0.1% (irradiance change of the order of –1 W/m^2, radiative forcing of –0.2 W/m^2; section 2.7). Following these results, the magnitude of the radiative forcing used in Chapter 9 for the Maunder Minimum period is relatively small (–0.2 W/m^2 relative to today).
Which if true (and this is going to be very short) leads one to the conclusion that the little ice age was very little and very local and may have had a lot more to do with volcanic activity then much else. Leaving us with the European Warm Period. There they won't even go out on a large tree trunk (Section 2.7 of WGI)
Prior to direct telescopic measurements of sunspots, which commenced around 1610, knowledge of solar activity is inferred indirectly from the 14C and 10Be cosmogenic isotope record in tree rings and ice cores, respectively, which exhibit solar related cycles near 90, 200 and 2,300 years. Some studies of cosmogenic isotopes (Jirikowic and Damon, 1994) and spectral analysis of the sunspot record (Rigozo et al., 2001) suggest that solar activity during the 12th-century Medieval Solar Maximum was comparable to the present Modern Solar Maximum. Recent work attempts to account for the chain of physical processes in which solar magnetic fi elds modulate the heliosphere, in turn altering the penetration of the galactic cosmic rays, the flux of which produces the cosmogenic isotopes that are subsequently deposited in the terrestrial system following additional transport and chemical processes. An initial effort reported exceptionally high levels of solar activity in the past 70 years, relative to the preceding 8,000 years (Solanki et al., 2004). In contrast, when differences among isotopes records are taken into account and the 14C record corrected for fossil fuel burning, current levels of solar activity are found to be historically high, but not exceptionally so (Muscheler et al., 2007).
Which leaves us precisely here



16 comments:

Anonymous said...

With such sparse data, I find it amazing that anyone would claim anythingabout the TSI during the maunder Min relative to today.

There have been only 3 decades of direct TSI measurements from satellites and, even with that record, the solar experts can not agree about whether TSI has remained constant!

Willson says TSI has changed 0.04% from one cycle to the next while other solar scientists imply it has barely changed that much over 300 years!

Whom should we believe?

EliRabett said...

Moi.

More seriously, this appears to knock the heavy breathing about why there is such a weak VLIA and EWP in the proxy records into a cocked hat. OTOH, there is enough uncertainty in everything (as you point out) to satisfy everyone.

Oh yeah, the suggestion is that you take a name on entering the comments. The dispenser is on the right.

Steve Bloom said...

IIRC about six months ago Tamino had a debate (on his blog) with Willson. I believe Willson was left without much of an argument.

Anonymous said...

Eli and Steve,

What then is your view of climate history on a global level from say 1000 to the present? Do you believe there was basically an even global temperature on average from 1000, with some regional fluctuations, until about 1980, after which we saw a global sharp rise?

I am not arguing whether this is right or wrong, just asking what your view is.

Frederic

Dano said...

Fascinating question Freddy asks in the post that linked to the ar4 forcings and a graph of the combined reconstructed temperatures. I guess the wish is that a first paper remains a totem.

They got nothin'.

Best,

D

Flavius Collium said...

The picture says it well and clear.

Anonymous said...

"IIRC about six months ago Tamino had a debate (on his blog) with Willson. I believe Willson was left without much of an argument."

Perhaps but the one critical point that Willson made is that when one only has 30 years of direct instrument measurement of TSI, one has to be very careful about making statements about the climatological significance of TSI in general.

One can accept the latter statement even if one does not accept Willson's claim about an increase in TSI over the past few cycles.

And on the latter subject, the jury is really still out among solar experts. The instrument record is so disjoint that both sides must make assumptions about how to piece things together in order to make their case. If there were a continuous record over the 30 years, I suspect that we would not have the ambiguity (at least not nearly so much).

--T

Steve Bloom said...

Frederic, IMVHO if irradiance changes are confirmed to be not likely to have been a factor (and that would indeed tend to make the trend over most of that time resemble the handle of a well-known winter sporting implement), there remain (at least) a) some major bumps from volcanic eruptions, b) the possibility of a degree of pre-industrial anthropogenic influence (per Ruddiman), and c) the further possibility of some degree of synchronization of the large-scale climate oscillations (per Tsonis; his particular idea has been dumped on by Tamino among others, but something along those lines will remain a live item until somebody comes up with an alternative explanation for the 1976 climate shift).

This all remains a fascinating subject, but it's very quickly losing its value for the denialists. (Actually I think it's already lost its value , but the denialists' behavior is like the proverbial dinosaur whose brain takes a minute or two to register the fact that its body has expired). Of course McIntyre know this, which is why he keeps casting around for a replacement point of attack. Eventually even his die-hard fanboys are going to get bored with further developments on the theme of why a now ten-year-old paper wasn't perfect even though its main conclusions have been upheld by subsequent work.

I agree, T, except to note that for many years the jury was assumed to be in until it was recently forced to go back out. That the jury was ever thought to be in (not just on irradiance, but on the MWP and LIA as major global events) seems to have been an artifact of the North Atlantic region having a pretty variable climate and the early climate researchers being largely from there.

Hank Roberts said...

I'm thinking of a different proverbial dinosaur, I forget the author who ogbserved that we have lots of really big dinosaur fossils, but very few babies of the same species, and imagined this communication down the spinal cord:

Front brain: Slow down, I think there's a cliff up ahead

Back brain: Plod, plod, plod ...

Front brain: Slow DOWN!

Back brain: Plod, plod, plod, plod

Front brain: HEY!

Back brain: Plod, plod ... eh? what?

Front brain: Stop, STOP, there's a CLIFF -- AAaaaaugh

Back brain: Plod, plod ... eh? Did you say something? Aaaaugh!

------
But seriously -- I notice the 'Solar irradiance' and the volcanic forcings have consistently matching downward bumps. Is that just unsorted variation showing up in both groups, or ....?

Flavius Collium said...

Offtopic and I must also say somewhat unsafe to view as it includes cruelty to animals, nevertheless, relevant to the Blog's Master:
http://www.youtube.com/watch?v=FrMcMHzGoBo
And this cruelty to humans:
http://www.youtube.com/watch?v=9Od92391upY&NR=1

Horatio Algeranon said...

Steve said "the denialists' behavior is like the proverbial dinosaur whose brain takes a minute or two to register the fact that its body has expired)."

Horatio says,

“The trend's the same,
How very lame,
Now, what ever shall we blame?”

A Tale of two Surface Stations

Steve Bloom said...

Nice work, Horatio!

cce said...

This is totally off topic.

Regarding the original Oregon Petition "review." The website has long said that it was "peer reviewed." Was the Soon/Baliunas paper that was published in Climate Research (and then expanded in E&E) a version of the same paper, or was it a different paper? Somewhere I got it in my head that it was the same thing.

Thanks!

EliRabett said...

The original Soon Baliunas and Robinsons paper did appear in some journals after the petition had been circulated. You can google them. The journals are not very impressive.

Hank Roberts said...

But seriously --

Just eyeballing it, with the normal human tendency to discover patterns whether they're there or not, I think I see times when the solar irradiance and the volcanic forcing vary the same way at the same time.

Obviously that's from before satellite data was available so I assume this is observations that overlap.

Just asking for a sanity check here -- coincidence at about 1500, 1600 and 1800?

Anonymous said...

I think if everything was as clear-cut as some delude themselves into thinking it is, this issue wouldn't be so contentious, and nobody would feel the need to draw battle-lines on what things mean. It smacks of all such discussions where a lack of facts are there, everything is emotional, and it mainly boils down to opinion and world view.

But maybe I'm a romantic at heart.

-- MA