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Little Ice Age – what caused it?

9 October 2013

At http://phys.org/print299786071.html … a new study by climate scientists at the University of Berne in Switzerland has been looking at the Little Ice Age. In classic terms this is a tale of two halves – divided by a reprieve during the 16th century (the Tudor Period) when grown up men wore pantie hose – right up to their bloomers. In contrast, it must have been cold in the 17th century as grown up men wore thick trousers and long coats and balanced tall hats on their heads.

The paper begins by telling us volcanic eruptions were responsible for reducing solar radiation and thereby global cooling between the 13th and 15th centuries. Okay, there were volcanoes – but what caused the volcanoes to blow? This bit is absent.

The cooling weather then accelerated the formation of sea ice in the northern seas which they say triggered a positive feedback process that shaped the Little Ice Age. Hence, what they have looked at, and modelled, are only those things they think are relevant, namely oceans and wind. Any connection with activity on the Sun, on the one hand, or any other kind of cosmic vector is also omitted.

The paper is by climate scientists and is restricted to what scientists have on their radar. However, the results turned out by the Swiss super computer are interesting, to say the least as they show fairly conclusively that a vector is required to kick start it all, and one that is capable of abruptly reducing the amount of sunlight reaching the surface of the Earth. In other words, an inactive Sun with a paucity of sun spots may have nothing whatsoever to do with the Little Ice Age – or the Ice Ages in general.

In conventional wisdom winter weather in Europe is governed by the North Atlantic Oscillation (NAO), an air pressure system seesaw between the Azores High and the Icelandic Low and this tends to produce mild winters across central and northern Europe (very mild in comparison with the same latitudes in N America). If the system is weak, cold winters set in. The NAO in combination with volcanoes has generally been considered responsible for the Little Ice Age – which continued, off and on, into the 19th century (or at least, temperatures in the 19th century were on average lower than they were in the 20th century). Now, it seems, the Swiss claim the Little Ice Age did not need the influence of the NAO – it could be driven purely as a consequence of strong and frequent volcanic eruptions that created reduced solar radiation. We may add to that equation, that bolide explosions and heavy meteor showers could theoretically achieve the same level of opaqueness in the upper atmosphere. Using a super computer they have managed to model a situation that Clube and Napier theorised 30 years ago, confirming that it is possible. The super computer was used to find a feedback process that was capable of triggering Little Ice temperatures. They applied volcanic eruptions as the vector and added a weakening in solar radiation into the models and six slightly different starting conditions were selected from simulation – and all of them initiated the same process. Namely, in the Barents Sea the sea ice mass grew and spread to sub-Arctic areas of the N Atlantic, where they subsequently melted. The freshwater inflow from the meltwater altered the density of the upper ocean which led to less warm water being transported into the north – which in turn boosted the growth of sea ice.

The researchers concluded, from simulations, that the Little Ice Age was primarily governed by external triggers. Volcanic activity and less solar radiation initially caused an increase in sea ice formation – independent of atmospheric circulation or the ocean conveyor belt system. Colder air over the Barents Sea migrated to Europe and caused the cooler temperatures. The importance of this article is that anyone suggesting it was as simple as that, prior to the publication, would have been considered entirely off the table, and many climate scientists would simply have not entertained it.

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