The Question of Black Carbon

Black carbon has only recently emerged as a known major contributor to climate change, especially for the Arctic. Formed by the incomplete combustion of fossil fuels, biofuels, and biomass, black carbon absorbs light more strongly than any other particulate matter, especially when deposited onto glaciers and snow cover. Here, it lowers their reflectivity, thereby absorbing atmospheric heat and resulting in earlier spring melt and higher temperatures.

New research, published in Atmospheric Chemistry and Physics, is attempting to address research gaps in this new but significant climate agent by quantifying and analyzing black carbon concentration and deposition in Svalbard, the major archipelago north of Norway.

The study, focusing on black carbon on the Holtedahlfonna glacier in Svalbard between 1700 and 2004, found significant rises in black carbon concentration from the 1970s until 2004 , with unprecedented levels in the 1990s.  Importantly, the study concludes that the increase in black carbon concentration “cannot be simply explained by changes in the snow accumulation rate at the glacier,” or simply by glacial melt and shrinkage in Svalbard. This indicates that black carbon was instead deposited in increasing quantities during this time period.

Burgerbukta Glacier, Svalbard. Courtesy of Wikipedia

The study raises some puzzling differences between black carbon concentrations and deposition in Svalbard and between previous data from other Arctic regions. While Svalbard’s black carbon values increased rapidly from a low point in 1970 until 2004, reaching a high in the 1990s, black carbon analyzed in Greenland ice cores indicated generally decreasing atmospheric black carbon concentrations since 1989 in the Arctic.

This difference is likely at least partly explained by differences in the specific methodologies used in the studies, such as the operational definition of black carbon that determined which size particles were included in the study.

The Svalbard study collected its data by filtering the inner part of a 125 m deep ice core from the Holtedahlfonna glacier through a quartz fiber filter. The filtrate was analyzed using a thermal-optical method, while previous comparable studies used an SP2 (Single Particle Soot Photometer) method. The different methodologies used between studies makes it hard to assess the validity of the studies’ findings.

Indeed, previous studies on black carbon on Himalayan and European ice cores have repeatedly shown different and contracting trends when measured with different analytical methods, even when studies examined the same glaciers. This indicates a significant need for more and improved research on black carbon research in the Arctic.

Burgerbukta Glacier, Svalbard. Courtesy of Wikipedia.
Burgerbukta Glacier, Svalbard. Courtesy of Wikipedia.

Black carbon concentrations, as the study reveals, are immensely complicated and depend on a variety of factors, such as air concentration of black carbon, the amount of precipitation, local wind drift patterns post-deposition, sublimation, and melt. Black carbon concentration can also be affected by sudden changes in snow and ice accumulation, or seasonal melt. These factors make it difficult for scientists to collect faithful data of black carbon concentration over time.

However, black carbon data in the Arctic is incredibly important: in the Arctic, black carbon is a more important warming agent than greenhouse gases. Its levels are intensely impacted from local and regional emission sources near Svalbard, such as forest and wild fires and flaring at gas wells in Russia, impacts that are difficult to accurately quantify, the researcher state.

While this study sheds light on recent trends of black carbon levels in Svalbard, it raises some key questions about the particle’s measurement, suggesting a need for further development of accurate black carbon measurement techniques and for further research on the role black carbon plays in Arctic warming.

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