A Brief History of the Earth's Climate : Everyone's Guide to the Science of Climate Change by Steven Earle

A Brief History of the Earth's Climate : Everyone's Guide to the Science of Climate Change by Steven Earle

Author:Steven Earle
Language: eng
Format: epub
Publisher: New Society Publishers


The Little Ice Age (LIA) was a period of consistently cool weather (and some particularly cold winters) that lasted for over 500 years from around 1300 to 1850,11 although the timing varies depending on the location and the type of evidence available for interpretation. It wasn’t a real ice age — no continental glaciers formed — and it wasn’t cold for that entire time, although there were some particularly cold periods, such as from 1450 to 1475 and from 1645 to 1715. During the Little Ice Age, glaciers advanced by hundreds to thousands of meters, in some cases crushing alpine villages, such as La Rosière in France (1616), Pre du Bar in Italy (1715), and a Tlingit village in Alaska. Significant glacial advances were also seen in central Asia.12 In fact, glaciers throughout the northern hemisphere advanced significantly during the LIA.

The Robson Glacier in the Canadian Rocky Mountains provides an example of a glacial advance around the time of the Little Ice Age (figure 7.7). At the height of the last glaciation, about 20 ka (20,000 years ago), the entire valley shown on figure 7.7 was filled with ice and the glacier extended nearly 20 km down the valley, only to join an even larger glacier there. Those glaciers all started receding at around 12 ka because of warming related to increased Milanković insolation, and by about 5.5 ka, this glacier had receded to a point about 4 km above its current terminus (behind Rearguard Mountain in the photo).13 At that time, it started to readvance, and it reached the limit shown by the terminal moraine at point B on figure 7.7 by around AD 1350. There is no evidence that this glacier advanced beyond that point during the rest of the LIA.14

A similar history is recorded for Switzerland’s Great Aletsch Glacier in (the longest glacier in Europe), as illustrated in figure 7.8. From around 3,500 years before the present until approximately AD 1350, the glacier’s terminus advanced and retreated several times, but its overall advance was in the order of 3 km. During the LIA, it also retreated and advanced, but it never advanced more than it had by AD 1350, and it never retreated more than approximately 1.5 km. Since 1850 it has retreated approximately 3.5 km.

Both of these glaciers expanded significantly over the past several thousand years, reaching maximum extents during the LIA, but these glacial expansions, which began millennia ago, cannot be correlated with the sunspot grand minima that took place between 1050 and 1800. Instead, they appear to be more closely correlated with a drop in Milanković insolation at 65° N that has taken place over the past several thousand years (figure 7.8) but actually started about 10,000 years ago. This conclusion is supported by Solomina and others15 who reviewed data from more than one hundred glaciers on all of the continents (except Australia) and noted a general trend of increasing glacier size in northern hemisphere glaciers during the past 10,000 years, corresponding with a decline in summer-time insolation at 65° N.



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