Little Ice Age Volcanism

17 Oct 2019

An interesting study by Luigi Bragato and Hanspeter Holzhauser - on volcanism and cooling temperatures which create conditions for pandemics (plague, cholera and influenza), in contrast to warmer periods when there is economic expansion and a lower incidence of natural disaster and outbreaks of disease. The major claim is that volcanism can cause century wide cooling. Is the latter sentence true ? - go to https://notrickszone.com/2019/10/14/new-paper-volcanism-can-cool-earth-f... ... the question is what triggered the Little Ice Age. It is suggested here that four tropical volcanoes erupted between 1275 and 1300AD and they were to blame. The persistence of cold summers in the aftermath is best explained by an expansion of sea ice and a related weakening of Atlantic ocean currents. Okay, that is Europe sorted - but what about the rest of the world?

We may note at this juncture that it is a study based on simulation. In other words, the result spewed out of the computer is the result of what is fed into the programme model. Other ingredients may be missing and a glaring one is the heightened instance of meteors and comets and other transient phenomena in the sky as recorded in Chinese and Korean astronomical records and portents (such as the Chosun Annals). Presumably meteorites, composed of dusty size objects, add debris to the upper atmosphere, and meteors exploding in the atmosphere, likewise. When added to the particles emitted by volcanoes we have a stronger case than presented so far. In a simulation the result is driven by the input so it is important that all factors are keyed in.

Scientists have theorised the LIA was caused by decreased summer solar radiation. Erupting volcanoes can do this, in the short term, by ejecting sulphur and other particles into the upper atmosphere, reflecting sunlight back into space. Presumably, if the Earth passed through a dusty area of space, such as the tracks of one of the Taurid streams, now much dissipated but spreading over a wider area of space, something similar could occur. An overload of the upper atmosphere creating an opaque sky in which sunlight was less powerful. However, the authors claim they have identified for the first time a 50 year spell of volcanism, and this is at the root of the Little Ice Age (setting it off). Anyone interested in what was occurring around 1300AD and the rest of the 14th century should read Mike Baillie's 'New Light on the Black Death: the Cosmic Connection' in order to understand the weather in Europe leading up to the most severe of the pandemics. In contrast, the basic premise of this new study is that these eruptions triggered a chain reaction that affected sea ice extent and ocean currents that lasted for centuries. 

As HH Lamb explained around 50 years ago cold weather (as a result of volcanoes and whatever might trigger it) also led to changes in oceanic currents and sea ice as a result of the polar zone expanding at the expense of the temperate zone. It is a feature of cold weather and this study uses that fact, as input, to infer it was volcanism that switched it on (like flicking an electric light switch on the living room wall). One moment the weather was warm and the next it was cold - but is this really what happened. Could a 50 year bout of volcanoes in the tropics really set in motion a cold period that lasted from 1300AD to 1700AD? The idea has been aired previously - by McGregor et al (2015) for example and by many earlier researchers (prior to the rise of CAGW). Scientists tend to accept a cause and effect associated with volcanoes as it is known that a big eruption can cause cool summers for a couple of years in the aftermath (and they can be easily picked out by dendrochronologists, Baillie's discipline). When it comes to prolonged cooling the connection is not so safe. One might even see volcanism, sea ice and ocean current changes as all symptoms of something else - and variously it has been considered solar insolation may have played a role. Indeed, we can even extend the LIA to 1850AD as there were two significant cooling periods in the 1740s and 1840s (as yet unexplained and perhaps cyclical in nature as the 1640s was the heart, or depth, of the LIA).

The Little Ice Age (LIA) was a period when average temperatures were lower than in the modern world - and lower than they were during the Medieval Warm Period (which is also part of the study). However, there were cold decades (really very cold) interspersed with decades which were not a lot different than modern temperatures. Likewise, in the Medieval Warm Period there were cold decades interspersed with warm decades - so the ocean currents were not permanently switched to another mode. The Sun might explain this - fading and sparking into life again. However, if the basic premise is right and it was aerosols and particles in the upper atmosphere that created an opaque sky some further research might be possible to see what other factors might impinge on this, boosting the volcanic output of sulphur and various other particles as no doubt volcanism was more common in the LIA than it is presently.

The first comment asks, what causes cycles in volcanism? The second comment says that what causes cycles in volcanism is the same as what causes cyclic mid ocean ridge earthquakes and what 'earth force' moves the tectonic plates. In other words, another factor is missing from the study - and has not been simulated. Something triggered the volcanism - and triggered a switch in ocean currents. What was that?