Maunder and Dalton Sunspot Minima

Pamela Gray says:
June 24, 2014 at 6:01 pm
Says nothing about the 1257 eruption, for the good reason that a strong effect from it on climate is not detectable, contrary to your claim.
Abrupt onset of the Little Ice Age triggered by volcanism and sustained by sea-ice/ocean feedbacks
Gifford H. Miller1,2,
Áslaug Geirsdóttir2,
Yafang Zhong1,
Darren J. Larsen1,2,
Bette L. Otto-Bliesner3,
Marika M. Holland3,
David A. Bailey3,
Kurt A. Refsnider1,
Scott J. Lehman1,
John R. Southon4,
Chance Anderson1,
Helgi Björnsson2 and
Thorvaldur Thordarson5
“Abstract
[1] Northern Hemisphere summer temperatures over the past 8000 years have been paced by the slow decrease in summer insolation resulting from the precession of the equinoxes. However, the causes of superposed century-scale cold summer anomalies, of which the Little Ice Age (LIA) is the most extreme, remain debated, largely because the natural forcings are either weak or, in the case of volcanism, short lived. Here we present precisely dated records of ice-cap growth from Arctic Canada and Iceland showing that LIA summer cold and ice growth began abruptly between 1275 and 1300 AD, followed by a substantial intensification 1430–1455 AD. Intervals of sudden ice growth coincide with two of the most volcanically perturbed half centuries of the past millennium. A transient climate model simulation shows that explosive volcanism produces abrupt summer cooling at these times, and that cold summers can be maintained by sea-ice/ocean feedbacks long after volcanic aerosols are removed. Our results suggest that the onset of the LIA can be linked to an unusual 50-year-long episode with four large sulfur-rich explosive eruptions, each with global sulfate loading >60 Tg. The persistence of cold summers is best explained by consequent sea-ice/ocean feedbacks during a hemispheric summer insolation minimum; large changes in solar irradiance are not required.”
Gifford Miller, of the dead moss clumps showing unprecedented warmth fame or infamy.
http://www.colorado.edu/news/releases/2013/10/23/cu-boulder-led-study-shows-unprecedented-warmth-arctic
Sorry to see you go over to the Dark Side, Pamela.
From supporting materials. Note reliance on Mann & models:
[12] The PDF peak defining abrupt LIA cooling 1275–1300 AD coincides with an interval of four large stratospheric sulfur loadings from explosive volcanism following a multi-centennial warm interval, during which complete revegetation of deglaciated sites would have fully reset the radiocarbon clock (Figure 2c). The PDF peak between 1430 and 1455 AD corresponds with a large eruption in 1452 AD, although the ages of the three largest 5-year bins appear to precede the eruption date. In contrast to the earlier 13th Century peak, the second PDF peak occurs at the end of a 150-year interval of variable but falling snowline (Figure 2c), raising the possibility that the PDF peak plausibly reflects a brief natural episode of summer cold that preceded the large 1452 AD eruption. Alternatively, the apparent lead of kill dates with respect to the 1452 eruption may be a consequence of combined measurement and calibration uncertainties.
[13] Volcanism exerts strong negative radiative forcing [Robock, 2000] that could easily explain the observed rapid snowline lowering, but the short residence time of stratospheric sulfate aerosols precludes a lasting influence on the regional energy balance from a single eruption. Decadally paced eruptions may produce greater cooling than a single large eruption if the recurrence interval is shorter than the upper ocean temperature relaxation time of decades [Schneider et al., 2009]. This may explain multidecadal cold episodes, but many Canadian sites that became ice-covered ∼1275 AD and ∼1450 AD, following episodes of strong explosive volcanism, remained continuously ice-covered until the most recent decade (Figure 2c). Such a long-lasting response suggests that explosive volcanism must have engaged a substantial and largely self-sustaining positive feedback(s).
[14] Climate modeling reveals one such possible feedback mechanism. Following Zhong et al. [2011], we tested whether abrupt LIA snowline depressions could be initiated by decadally paced explosive volcanism and maintained by subsequent sea-ice/ocean feedbacks. We completed a 550-year transient experiment (1150–1700 AD) using Community Climate System Model 3 [Collins et al., 2006] with interactive sea ice [Holland et al., 2006] at T42 × 1 resolution. Our transient simulation was branched off a 1000 AD control run, and forced solely by a reconstructed history of stratospheric volcanic aerosols and relatively weak solar irradiance changes (Figure 2b) [Gao et al., 2008]. Details of the experimental conditions are given in the Text S1. In addition to a continuously sustained sea-ice expansion following the late 13th Century eruptions (Figure 3b), the simulation also shows a sustained weakening of northward heat transport in the North Atlantic averaging 0.04 PW less than the mean of our control from 1300–1600 AD (Figure 3d; statistically significant at the 99.9% level), and an anomalously cold and fresh North Atlantic subpolar gyre (Figure S5). A significant increase in April-September surface albedo poleward of 60°N (Figure S4) results in a net summertime energy decrease of ∼1.5 Wm−2 averaged over the three centuries following late 13th Century eruptions. Albedo increase, expanded sea ice, and lowered ocean temperatures produce a persistent reduction in summer air temperature across Arctic North Atlantic continents (Figure 2e), consistent with our primary observations of expanded ice caps at this time. In a sensitivity test using the same model, initial conditions, and 13th Century volcanic forcing, Zhong et al. [2011]showed that increased southward sea ice export following the eruptions led to freshening and vertical stratification of the North Atlantic subpolar gyre, reducing open ocean convection and thus weakening the Atlantic meridional overturning circulation. These changes reduced basal sea-ice melt sufficiently to produce an expanded sea-ice state that persisted in the model for more than a century after the final eruption, without additional forcing. These mechanisms are similarly engaged in our transient simulations, suggesting that the initial snowline depression may have been sustained by the sea-ice/ocean feedback identified byZhong et al. [2011] for centuries after the initiating eruptions.
image
Figure 3. Climate model results for 1000 AD control (black), and volcanically perturbed transient beginning 1150 AD (red). Black dashed lines and gray bars represent mean and standard deviation of the control. (a) Monthly global downwelling surface shortwave radiation anomalies forced by aerosol loadings [Gao et al., 2008] after 1150 AD; earlier portion is unforced control. (b) Yearly and 30-year running mean of NH sea ice volume in Sept. from perturbed transient compared to control from its branching point. (c) 30-year running mean of the northward heat transport in the North Atlantic at 26°N. (d) 30-year running mean of average summer (JJA) surface air temperature over North Atlantic Arctic land (>60°N and 90°W to 30°E).
[15] Sea ice is the largest contributor to enhanced Arctic climate sensitivity [Serreze and Francis, 2006], and our transient simulation indicates that repeated explosive volcanism might have led to a persistent expansion of sea ice state during the LIA. This possibility is reinforced by a reconstruction of the abundance of sea ice in surface waters north of Iceland (Figure 2e). Sea ice does not form around Iceland; it only appears when there is a large export of sea ice from the Arctic Ocean. Sea ice was rarely present on the North Iceland shelf from 800 AD until the late 13th Century, when an abrupt rise in sea-ice proxies suggests a rapid increase in Arctic Ocean sea ice export, followed by another increase ∼1450 AD, after which sea ice was continuously present until the 20th Century [Massé et al., 2008] (Figures 1 and 2e). The increase in sea ice north of Iceland at the start of the LIA, and its persistence throughout the LIA, supports our modeling experiments suggesting explosive volcanism and associated feedbacks resulted in a self-sustaining expanded sea-ice state beginning 1275–1300 AD. Additional support for regional cooling beginning in the late 13th Century comes from the inversion of temperatures measured in a borehole through the south dome of the Greenland Ice Sheet (Figure 1). Although the temporal resolution is muted by thermal conductivity and ice flow, the pattern of temperature change (Figure 2f) [Dahl-Jensen et al., 1998] closely resembles our ice-cap growth histories, whereasδ18O values from the ice cores are poorly correlated with the borehole record, presumably because they are dominated by winter temperatures and changing seasonality of precipitation [Vinther et al., 2010].
[16] Our precisely dated records demonstrate that the expansion of ice caps after Medieval times was initiated by an abrupt and persistent snowline depression late in the 13th Century, and amplified in the mid 15th Century, coincident with episodes of repeated explosive volcanism centuries before the widely cited Maunder sunspot minimum (1645–1715 AD [Eddy, 1976]). Together with climate modeling and supported by other proxy climate reconstructions, our results suggest that repeated explosive volcanism at a time when Earth’s orbital configuration resulted in low summer insolation across the NH acted as a climate trigger, allowing Arctic Ocean sea ice to expand. Increased sea ice export may have engaged a self-sustaining sea-ice/ocean feedback unique to the northern North Atlantic region that maintained suppressed summer air temperatures for centuries after volcanic aerosols were removed from the atmosphere. The coincidence of repeated explosive volcanism with centuries of lower-than-modern solar irradiance (Figure 2a) [Schmidt et al., 2011] indicates that volcanic impacts were likely reinforced by external forcing [Mann et al., 2009], but that an explanation of the LIA does not require a solar trigger.

Alec Rawls says:
June 24, 2014 at 5:37 pm
Whether solar activity in the second half of the 20th century was “exceptionally high” or merely “high” makes no difference for the question of whether it could explain late 20th century warming. So long as the climate system has not yet equilibrated to a higher level of forcing (by whatever mechanism that forcing is transmitted) then warming will continue until equilibration is reached, and there is no reason to think that equilibration does not take many decades.
You will have to say ‘centuries’ as solar activity was as high in the 18th century as in the middle 20th.
Dr Norman Page says:
June 24, 2014 at 5:55 pm
The DY3 data is a beautiful…
There is general consensus that the Dye3 data is awful, because of the complex ice flow regime at Dye-3, where ice from the oldest strata has experienced significantly different summer melt and accumulation conditions than observed presently at the Dye-3 drill site.
Scientific insight is the ability to know which cherries to pick
So you are an excellent cherry picker, I won’t disagree with that.

LT says:
June 24, 2014 at 7:28 pm
of course there is a long term increase
You state that without evidence and as a belief [“of course”]

lsvalgard,
The cosmogenic Isotope proxy clearly shows a long term increase in solar activity, I thought that was an accepted metric. Please correct me if I am in error.
http://en.wikipedia.org/wiki/Solar_variation#mediaviewer/File:Solar_Activity_Proxies.png

LT says:
June 24, 2014 at 7:43 pm
The cosmogenic Isotope proxy clearly shows a long term increase in solar activity, I thought that was an accepted metric. Please correct me if I am in error.
Both the sunspot number shown and the cosmogenic record are not what we today think are the correct versions. For the sunspot number see Fig. xx4 of http://www.leif.org/research/ISSI-Book-Section-4.pdf and for the isotopes see Figure 2 of http://www.leif.org/research/Svalgaard_ISSI_Proposal_Base.pdf [note the team members]

Willis Eschenbach: The accuracy of the ‘hockey stick’ type reconstruction shown above was essentially confirmed by The National Academies of America in 2006 with their paper ‘Surface temperature reconstructions for the past 2000 years.
So that’s what you mean. I think the reference is to the use of the most important principle components of multiple time series, followed by an attempt to derive a linear relationship between temperature and the principle components by some form of linear regression. MBH98 was the first such effort in climatology, and the the method has been widely applied since then. MBH98 contained errors, which were pointed out by McIntyre and McKittrick, whose work was in turn shown to have some errors (though more minor.) Mann has continued to publish, better work, the best of which does not support the MBH98 and elaborated “Hockey Stick” (though he seems to claim it still does), which “hockey Stick” itself was disconfirmed by others and isn’t any longer accepted by the UNIPCC or anybody else who pays attention to details.
In 2007, the NAS was not quite ready to commit to the idea that Mann may have been worse than sloppy, as I was not quite ready at that time. I think careful reading of Mann’s work, McIntyre’s careful critiques, the the full interchange published in Annals of Applied Statistics, and other work undermines belief in Mann’s honesty. But I still think that tonyb’s (and others’) strategy of debating Mann head on is defensible.
thank you for your later reference to my patience. It is a strategy. I am able to take out my frustrations in chopping trees, hefting heavy stones, and digging and hauling dirt in the carrying out of “landscaping” projects. In person I am actually crabby.

As you can see, there is much support for the “solar minima cause cool temperatures” hypothesis in the CET, in all three of the coldest periods.?w=840