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Visualizing Change

Climate change is one of those very difficult things to see first-hand, in that we need some form of historical reference and a clear link to warming. Further, the reference point needs to be visual and significant to have an impact. Sea level is one such reference, although in the clear majority of cases it moves so slowly that any reference to the past is almost impossible to discern. I lived in seaside areas on and off for several years in the 1970s and 1980s, but returning 30-40 years later offers little to no visual hint of change, even though change is underway.

I recently visited Chamonix in France where a very significant change is both underway and clearly visible. You can take the rack and pinion railway nearly a kilometre vertically from the town up to Montenvers, where the Mer de Glace glacier can be viewed and visited. This is the longest and largest glacier in France, and the second longest in the Alps. The scene from Montenvers, like much of the Alps, is beautiful, although the glacier itself is not easy to visualize in that its surface is largely covered with a dusting of debris from sides of the valley. Nevertheless, it is an imposing scene and more than worth the visit.

But this is just the beginning of the story. The glacier is shrinking rapidly, the first indication of which comes from the viewing sign that includes a dotted line showing the height of the glacier in 1820. The drop in height is very significant, but if that isn’t sufficient visualization of change, then a walk down a rocky path from Montenvers and then finally some 400+ steps to the glacier surface not only brings home the scale of change but also the rate – which appears to be accelerating.

The first impression comes when the hiker arrives at the 1820 line, well above the current glacier. This is quite a sobering moment in that there is no sign of ice, just summer wildflowers and trees.

This is just the first of many year signs, but the impression of acceleration comes lower down. Once the stairs are reached the first of several closely spaced signs appears, this one for 1990.

Soon after that comes 2003 (bottom right corner of the picture) and then finally the surface of the glacier itself, which brings the hiker to 2017. The drop from 1990-2003 was sizable for 13 years, but seemed small compared to the 2003-2017 change (14 years). The first drops from 1820 to 1920 and then 1985 seemed smaller by comparison.

The changes to the Mer de Glace have been widely recorded and written about, including an excellent report on the rate of decline based on Landsat satellite images. In its 5th Assessment report the IPCC noted the general demise of mountain glaciers as follows;

Despite their variability due to different response times and local conditions, the annually measured glacier terminus fluctuations from about 500 glaciers worldwide reveal a largely homogeneous trend of retreat. In Figure 4.9 (see below for the Central Europe extract), a selection of the available long-term records of field measurements is shown for 14 out of the 19 RGI regions. Cumulative values of retreat for large, land-terminating valley glaciers typically reach a few kilometres over the 120-year period of observation. For mid-latitude mountain and valley glaciers, typical retreat rates are of the order of 5 to 20 m/year. Rates of up to 100 m/year (or even more) are seen to occur under special conditions, such as the complete loss of a tongue on a steep slope, or the disintegration of a very flat tongue.

Cumulative length change in metres vs. year

Recognizing that the reasons for change for any given glacier can be many and varied, the global trend is very clear and Mer de Glace is one example of this. If you are in the region over the summer vacation period then a visit is highly recommended, with the bonus of being able to walk inside the glacier when you finally reach the surface, thanks to some ingenious tunneling by the local tourist authorities.


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