Sunday 19 January 2014

The end of the Little Ice Age.

The 'Little Ice Age' was a prolonged cooling of the climate from roughly 1650 till roughly 1850 (estimates vary). It is well documented in Europe, but does not appear to be global in extent; evidence from glaciers in North and South America and New Zealand suggests that these areas were effected to some extent, but the literate cultures of East Asia have no record of such a chilling. It was clearly not a true Ice Age, which involve glaciers covering large parts of the temperate continents for tens of thousands of years, but was too long for most short term climate effects; for example cooling caused by major volcanic eruptions seldom lasts more than a decade.

Pompenburg met Hofpoort in de winter, showing skaters on a frozen canal in Rotterdam in 1825. Bartholomeus Johannes van Hove.

The Little Ice Age ended as mysteriously as it began, starting with the abrupt withdrawal of the Alpine Glaciers from 1865 onwards, despite the fact that temperatures in the Alps were somewhat cooler at this time than they were in the mid eighteenth century (temperatures did not start to rise in the Alps until around 1910).

In a paper published in the Proceedings of the National Academy of Sciences of the United States of America on 17 September 2013, a team of scientists led by Thomas Painter of the Jet Propulsion Laboratory at the California Institute of Technology, describe the results of an attempt to model the end of the Little Ice Age, and their conclusions about the cause of this.

Painter et al. conclude that the end of the Little Ice Age was directly linked to the onset of the Industrial Revolution, which started in Britain in the mid-eighteenth century, spread to France at the beginning of the nineteenth century, and the rest of Western Europe by the middle of the century.

They assert that the glaciers were melted not by higher atmospheric carbon dioxide levels raising the atmospheric temperature, but rather by soot from industrial chimneys settling on the glaciers and changing their albedo (reflectiveness). Snow and glaciers are normally white, and highly reflective, so that most of the light reaching them is reflected back into the atmosphere. However a glacier coated by a layer of black soot will absorb sunlight as heat, making it likely to melt rapidly.

Coalbrookdale by Night, showing fires and smoke in the Shropshire village in 1801. Philip James de Loutherbourg.

Painter et al. also suspect that the glaciers became particularly vulnerable as steam railways penetrated the Alps,which brought people close to view the glaciers as part of a growing tourism industry in the area, and with them a source of soot emissions closer than any previous development.

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