End of the Little Ice Age in the Alps forced by industrial black carbon

Abstract

Glaciers in the European Alps began to retreat abruptly from their mid-19th century maximum, marking what appeared to be the end of the Little Ice Age. Alpine temperature and precipitation records suggest that glaciers should instead have continued to grow until circa 1910. Radiative forcing by increasing deposition of industrial black carbon to snow may represent the driver of the abrupt glacier retreats in the Alps that began in the mid-19th century. Ice cores indicate that black carbon concentrations increased abruptly in the mid-19th century and largely continued to increase into the 20th century, consistent with known increases in black carbon emissions from the industrialization of Western Europe. Inferred annual surface radiative forcings increased stepwise to 13-17 W·m −2 between 1850 and 1880, and to 9- etween the end of the 13th and the middle of the 19th centuries, glaciers in the European Alps were considerably larger than at present (1). Beginning around 1865, however, glaciers across the Alps retreated rapidly to lengths generally shorter than in the known range of the previous 500 y (1), continuing to present day with interruptions by only minor advances (Fig. 1). This relatively abrupt retreat from the mid-19th century maximum is often considered by glaciologists to be the end of the Little Ice Age (LIA) (1-3).Glaciologists have conjectured that increasing temperatures (4) and decreasing precipitation (2) caused the rapid observed retreat of glaciers throughout the Alps in the second half of the 19th century. However, such scenarios are inconsistent with temperature records and climate proxies for the Alps (5, 6). During the latter half of the 19th century and early 20th century, when glaciers were retreating rapidly, temperatures in the Alpine region were apparently cooler than in the late 18th to early 19th centuries (Fig. 2) and precipitation was largely unchanged (5-7). Glaciers subject to these climate forcings alone would have had positive mass balance and advanced (8), rather than retreated, as observed.The density of temperature and precipitation observations in the Alps before 1800 was less than one-third that after 1860, by which time the density reached near its current level (5). Nevertheless, with our current knowledge of the Alpine climate, climatologists consider the climatic end of the LIA to have come markedly later than the glaciological end, resulting in a paradox (2).Simulations of glacier-length variations using glacier flow and mass balance models forced with instrumental and proxy temperature and precipitation fail to match the timing and magnitude of the observed late 19th century retreat (8)(9)(10)(11)(12). Matches between simulations and observations have only been achieved when additional glacier mass loss is imposed after 1865, or when precipitation signals are generated that would fit the glacier retreat rather than using actual precipitation records (8,10,12,13). Therefore, explaining the glacier retreat with climatic variables requires climate forcings that are inco...

Testing the consistency between changes in simulated climate and Alpine glacier length over the past millennium

“…The successful application of global climate models driving a global glacier model over the past millennium also reinforces the validity of this approach to study future changes on similar timescales. Some studies have argued that the large melting of Alpine glaciers in the 19th century might be due to a modification of the ice albedo caused by the deposition of black carbon of anthropogenic origin (Painter et al, 2013). This hypothesis has recently been challenged (e.g.…”

Little Ice Age climate reconstruction from ensemble reanalysis of Alpine glacier fluctuations

“…The frequent short phases of very low ELA during the LIA can be mostly explained by the effect of volcanic eruptions on incoming radiation. Also, the rapid melt-back of the glaciers after 1860 can be explained by temperature alone, without additional albedo changes due to black carbon (Painter et al, 2013).…”

“…More qualitatively, Nussbaumer et al (2011) conclude that "a combination of low solar forcing, frequent and strong volcanic eruptions, and dynamic effects due to internal variability of the climate system led to the prominent glacier advances during the LIA". The rapid recession of the glaciers after 1865 has been explained by glacier surface darkening, and thus albedo reduction, by increasing release of industrial black carbon (Painter et al, 2013).…”

Little Ice Age and contemporary glacier extent in the Western and South-Western Piedmont Alps (North-Western Italy)

“…In the European Alps, glacier extent has dramatically changed since the end of the Little Ice Age (LIA) (around 1865; Painter et al, 2013), with an overall decrease in ice coverage of about 50% (Zemp, Paul, Hoelzle, & Haeberli, 2008). Due to the specific physiographic and geographic settings, glacier shrinkage has been as much as 80% in the Western and South-Western Piedmont Alps, which are the focus of the current study (Fioraso, Bertotto, Lucchesi, Nigrelli, & Chiarle, 2013).…”