Glacial History

This article may be a bit of a stretch so far as covering policy goes, but it does factor into the global climate change discussion in an interesting way and presents a unique historical example of industry’s impact on climate. The article, published in the latest Proceedings of the National Academy of Sciences, examines the end of the Little Ice Age, a period of cooling which ran roughly from the sixteenth to the nineteenth century, though definitions of the period are now being seen to vary depending on local and regional climate regimes. In particular, the paper looks at the receding of glaciers in the Swiss Alps, which has presented climatologists and glaciologists with a remarkable mystery for some time now.

What is so perplexing about the receding of these alpine glaciers is the timing. According to reconstructions of the regions climate from historical weather records, the glaciers should have continued growing into the early twentieth century, beginning to recede when the area’s own period of cooling began to ebb around 1910. Instead, the area’s glaciers began to recede in 1865, well before the general climate shift, begging the question of why?

Well as the paper points out, this turning point in glaciations, 1865, falls shortly after the end of the Industrial Revolution, when European carbon emissions were climbing to new heights which would not begin to fall again until the 1970s. Previous analyses of black carbon deposits in ice cores have only reached back to the turn of the century, which gave an incomplete picture of the situation, showing a steady level of carbon deposition from 1900 on. This paper though, goes back further in the ice record (using deeper samples from a new location) and shows that this plateau at 1900 is itself a marked increase from pre-1860 levels, meaning that around the time the glaciers began to beat their premature retreat, the area also saw considerable increases in black carbon emission.

The researchers examine this possible relationship and find their connection in a phenomenon called radiative forcing. This is basically the difference between the energy the sun hits the earth with and the energy the earth reflects back, or more directly, the energy the earth absorbs from the sun. A more negative forcing indicates a cooling effect, a more positive forcing a warming one. Now any number of things can affect radiative forcing, from cloud cover to the color of the ground being exposed to atmospheric composition (hence our general concern with greenhouse gases). In this case, the black carbon being deposited across the Alps leads to greater radiative forcing, thus leading to glacier recession without any significant changes in overall climate. This is a result of changes in the landscape’s albedo, more or less its whiteness, which determines the level of radiation it reflects. By shifting the landscape’s albedo, black carbon deposits result in greater absorption of energy, which in turn raises the ground’s temperature without affecting climate. It is worthwhile to note, as the researchers themselves do, that there a number of factors that could affect this analysis which cannot be considered because of insufficient data. As a result, it is difficult to draw a clear causative line between these two events: increased carbon deposit and glaciers melting. At the same time, their model predicts levels of glacier loss similar to historical levels when run with the presence of black carbon and lined up with climate records from the period.

Like I said, this isn’t exactly a policy story. But it does cross paths with environmental policy in a few interesting ways. For example, shortly after this glacial retreat began, the world saw the birth of a number of incredibly important inventions, including such modern-day mainstays as the internal combustion engine, the telegraph, and the radio. Maybe not so much a mainstay for the telegraphy, but you get the point. These are now everyday parts of our lives, much in the same way that by 1865, steel and textile mills had become everyday vestiges of life in post-Industrial Revolution Europe. Seeing now how those revolutionary steps forward impacted the environment, it does reinforce the need for questions about the technologies which have since revolutionized our lives. There is a lot of information out there about how human industry has affected the world on a global scale, and a lot of contrary narratives jostling for dominance in the public consciousness with regards to how much change is natural and how much we as a species have caused. With a study like this, it seems as if the natural rhythms of the earth were disrupted by something, and that something seems to line up remarkably well with human activity. As the authors point out, it is difficult to draw an absolute causative relationship in these situations, simply because of the immense and exhaustive amount of data necessary to draw those types of conclusions. But how much could it honestly hurt to err on the side of caution? Because it could cost us a lot more not to.

Original article: http://www.pnas.org/content/110/38/15216.full.pdf+html

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