Thursday, 31 October 2013

Evidence that the Little Ice Age in Europe was a Global Phenomenon

Climate scientists have traditionally held the view that the extended period of cooling experienced in Northern Europe, most severe around 1645-1715, was a regional phenomenon. It coincided with a marked decrease in solar activity (the so called Maunder Minimum), as did also the less severe European cooling associated with the later Dalton Minimum. These two extended sunspot minima, along with the late 20th Century Modern Maximum, are illustrated here:

Central England Temperature records going back to 1650 correlate closely with these periods of decreased solar activity, even the modest lapse in solar output which occurred in the 1960's/70's. It is clear that during the Little Ice Age associated with the Maunder Minimum, winters in Britain were more often than not very harsh indeed and summers were often wet and miserable, resulting in many crop failures. Historical records show that the cooling was simultaneous across much of Northern Europe, across mid-latitude Asia and into North America. So, in extent at least, there is firm evidence that the Little Ice Age was a mid-latitude Northern Hemisphere phenomenon.

The cooling appears to have been particularly severe in North Western Europe and may have been exacerbated here by a weakening of the North Atlantic Oscillation (NAO), precipitated by, or merely coincidental with the decrease in solar activity, with a consequent 'slowing' of the Jet Stream, causing it to track much further south. The NAO, via the Gulf Stream, via the North Atlantic Drift, is largely responsible for the pleasantly mild maritime conditions experienced in NW Europe, particularly during winter. During the LIA, it seems that our winters hailed largely from the continent, from the much colder east and north east, as was the case during the winters of 2009/10 and 2012/13. The Jet Stream during these most recent periods was noticeably far south, allowing much colder air from Siberia and the Arctic to penetrate our shores. The pattern of a south-tracking Jet Stream was established during the summer of 2012 when it sat over the UK, instead of being north of us, resulting in the now infamous washout summer of flooding. Come winter, it moved even further south, depriving us of our typical mild wet winter which was replaced by a much colder continental one, lasting well into late Spring.

So, why is all this so important right now? Well, for a start we are definitely looking like we are headed into Dalton Minimum territory in terms of solar activity during the present cycle (SC24) and on into the next. But here's where it gets interesting: Mike Lockwood of Reading University has increased his estimate of the probability of the Sun lapsing into Maunder Minimum type solar activity from 8% to 25-30% and he says that a repeat of a Dalton Minimum is 'more likely than not' (IPCC speak!). He related this information to Paul Hudson, Look North BBC Weather Presenter, and Paul wrote a blog post which appears to have stirred up a real hornet's nest, not least comprised of stinging comments from Lockwood himself who claims that the Hudson blog has misrepresented him.

The basic gist of Hudson's blog is that there is now a real possibility of Little Ice Age type conditions impacting upon us in the UK and in Northern Europe. Lockwood's research confirms this possibility of regional cooling, though he is careful to stress that it is only regional and that it must be viewed in the context of the wider effects of CO2 induced global warming, which he considers are still pre-eminent. So any UK cooling, though possibly severe in the short term, would presumably be eventually aced by anthropogenic CO2 and, on a global scale, Lockwood clearly states that even a repeat Maunder Minimum would have little, if any impact.

Hudson takes a slightly different view and raises the possibility in his blog that, according to research by Mann et al, 2001, global temperatures might also be expected to nose-dive by 0.3C to 0.4C, smaller than the regional change, but still significant, enough to wipe out the warming seen since the 1950's. How Lockwood comes to the conclusion that this addition by Hudson somehow misrepresents what he has to say about regional climate change, I don't quite figure. I suspect he is just a bit miffed that Hudson took the step further in his blog and is concerned now that others might therefore misquote him: Paul Hudson certainly did not and he quite rightly stands by his blog post. Just for the record, here is what Mike Lockwood has said on Facebook:

"It amazing how one can be misrepresented no matter how clear one tries to make it! One point I made to Hudson is that many of the so called bits of "evidence" for solar influence on global temperature actually come from Europe in winter (cf Eddy and all that) and so are not global at all. Depressing.

So there is absolutely no misunderstanding here - I too am 'vociferous advocate' of (the known science that anthropogenic greenhouse gases causes) global warming!

Since 1985. I've explained below I am only talking about a possible (stress possible) solar influence on European blocking events and not at all about global temperatures. But it is a fact that solar activity HAS declined since 1985, the "exceptional" long and low solar minimum of 2008/9 and the current very weak cycle 24 are both part of that trend and we are now back to conditions last seen around 1920.

Hi David, Bru - too right I am only talking of regional effects!!!!!!!!!!!!!!!!! On the global front I refer you to Jones, Stott and Lockwood (JGR 2012 doi: 10.1029/2011JD017013) in which we showed that even a Maunder minimum would have almost no effect on global temperatures - very similar to the result in Stefan's paper. I have always made it clear (and did make it absolutely clear to Paul Hudson - I couldn't have stressed it more!) that I am only talking about blocking events so for example if such an event brings cold Arctic air to central Europe in winter, it takes warm moist air up to Greenland. The offending web pages had disappeared when I looked so I have no idea how badly I am being misquoted and misrepresented here. I'd point you at a review I wrote last year Lockwood, M. (2012) Solar influence on global and regional climates. Surveys in Geophysics, doi: 10.1007/s10712-012-9181-3 which also makes it absolutely clear that although there is some (as yet not cast iron) evidence for European winters of some solar effects theres none on a global basis."

Note what Lockwood says about evidence for the effects of solar activity on winters globally - there is none according to him. I'm here to tell you that there is some! In point of fact, the evidence for a simultaneous global impact of the Maunder Minimum is quite extensive and growing, due to increased coverage of proxies from the Southern Hemisphere, in particular Antarctica. Scripps Institution of Oceanography, UC San Diego graduate Orsi et al analysed data from an ice core drilled into the West Antarctic Ice Sheet and found that, during the LIA Antarctic temperatures were an average 0.52 ± 0.28°C colder than the last 100-year average. It should be stressed that this was contemporaneous with the temperature drop in the Northern Hemisphere, therefore did not involve a simple redistribution of heat around the globe. I quote:

"The period between 1400 and 1850 was marked by an average temperature drop of just less than 1 degree C (1.8 degrees F), but not just in the Northern Hemisphere. Scripps graduate student Anais Orsi and colleagues found evidence of the same cooling trend in samples of ice from the West Antarctic Ice Sheet. That contradicts prevailing theories that the Little Ice Age was not globally synchronized, but a regional cooling possibly triggered by changes in ocean circulation that created a temperature see-saw effect between the hemispheres."

A good summary by CO2 Science of various papers pointing to the global aspect of the LIA can be found here.

The Simms et al paper mentioned in the above link can be found here. CO2 Science says (of this paper) that:

"Although Simms et al. write that initial studies on ice cores "suggested that the timing of the most recent Neoglacial advance in West Antarctica may have been out of phase with the Little Ice Age in the Northern Hemisphere (Mosley-Thompson and Thompson, 1990)," they report that other ice core records from East Antarctica and elsewhere in West Antarctica support an in-phase relationship between climate events in the two hemispheres, citing the work of Li et al. (2009) and Bertler et al. (2011). And they add that the marine record provides ample evidence "for cooler conditions around ~250-550 calBP (1400-1700 AD)," citing the studies of Domack and Mayewski (1999), Brachfeld et al. (2003), Yoo et al. (2009), Hass et al. (2010) and Shevenell et al. (2011)."

I let CO2 Science have the last word here as the author states very clearly and eloquently the following:

"Clearly, the greater weight of real-world evidence in this controversy resides with Simms et al. and the many other researchers who have identified and dated a Little Ice Age in various parts of Antarctica that coincides in time with the Little Ice Age of the Northern Hemisphere. And that dating of the Little Ice Age, plus the comparing of its temperature with the temperatures that both preceded and followed it, also pretty much confirms the existence of the Medieval and Current Warm Periods in Antarctica, which are thus found to have occurred contemporaneously with the Medieval and Current Warm Periods in the Northern Hemisphere. And when viewed in this global and oscillatory context (and when extended even further back in time through the Dark Ages Cold Period and the Roman Warm Period), it becomes ever more clear that there is nothing unusual, unnatural or unprecedented about the global warming of the 20th century. Nor is there any need to invoke atmospheric CO2 enrichment as the driver of 20th-century warming, as previous equivalent ups and downs in earth's surface temperature occurred during times of both low and relatively constant values of the air's CO2 content."

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