A NASA-led team of scientists has uncovered strong evidence that coal soot from a rapidly industrializing Europe caused the abrupt retreat of mountain glaciers in the European Alps that began in the 1860s, a period often thought of as the end of the Little Ice Age (LIA). An open access paper on the study is published in the Proceedings of the National Academy of Sciences.
Radiative forcing by increasing deposition of BC is unique in explaining the Alps glacier retreat from the LIA in the mid-19th century while maintaining consistency with the temperature and precipitation reconstructions. The BC hypothesis is not refuted by any available records, or by the calculations presented here. This impact of BC on glacier mass balance in the Alps pushes our understanding of the onset of anthropogenic influence back further than CO2 forcing alone would indicate.
...The potential implication of BC deposition in the end of the glacial LIA in the European Alps and the growing understanding of the magnitude of radiative forcing by dust and BC suggests that studies of past, present, and future changes in glacier mass balance should consider these albedo-driven changes to ensure physical consistency.—Painter et al.
In the decades following the 1850s, Europe underwent an economic and atmospheric transformation spurred by industrialization. The use of coal to heat homes and power transportation and industry in Western Europe began in earnest, spewing huge quantities of black carbon and other dark particles into the atmosphere.
Black carbon is the strongest sunlight-absorbing atmospheric particle. When these particles settle on the snow blanketing glaciers, they darken the snow surface, speeding its melting and exposing the underlying glacier ice to sunlight and warmer spring and summer air earlier in the year. This diminishing of the snow cover earlier in each year causes the glacier ice to melt faster and retreat.
The Little Ice Age, loosely defined as a cooler period between the 14th and 19th centuries, was marked by an expansion of mountain glaciers and a drop in temperatures in Europe of nearly 1.8 degrees Fahrenheit (1 degree Celsius). But glacier records show that between 1860 and 1930, while temperatures continued to drop, large valley glaciers in the Alps abruptly retreated by an average of nearly 0.6 mile (1 kilometer) to lengths not seen in the previous few hundred years. Glaciologists and climatologists have struggled to reconcile this apparent conflict between climate and glacier records.
Something was missing from the equation. Before now, most glaciologists believed the end of the Little Ice Age came in the mid-1800s when these glaciers retreated, and that the retreat was due to a natural climatic shift, distinct from the carbon dioxide-induced warming that came later in the 20th century. This result suggests that human influence on glaciers extends back to well before the industrial temperature increases.— Thomas Painter, a snow and ice scientist at NASA’s Jet Propulsion Laboratory, and study leader
The researchers studied data from ice cores drilled from high up on several European mountain glaciers to determine how much black carbon was in the atmosphere and snow when the Alps glaciers began to retreat. Using the levels of carbon particles trapped in the ice core layers, and taking into consideration modern observations of how pollutants are distributed in the Alps, they were able to estimate how much black carbon was deposited on glacial surfaces at lower elevations, where levels of black carbon tend to be highest.
The team then ran computer models of glacier behavior, starting with recorded weather conditions and adding the impact of the lower-elevation pollution. When this impact was included, the simulated glacier mass loss and timing finally were consistent with the historic record of glacial retreat, despite the cooling temperatures at that time.
We must now look more closely at other regions on Earth, such as the Himalaya, to study the present-day impacts of black carbon on glaciers in these regions.—Georg Kaser, a study co-author from the University of Innsbruck
Kaser is also lead author of the Working Group I Cryosphere chapter of the Intergovernmental Panel on Climate Change’s (IPCC) upcoming Fifth Assessment Report.
Thomas H. Painter, Mark G. Flanner, Georg Kaser, Ben Marzeion, Richard A. VanCuren, and Waleed Abdalati (2013) End of the Little Ice Age in the Alps forced by industrial black carbon. PNAS doi: 10.1073/pnas.1302570110