Around 150 years ago, towards the end of the period often referred to
as the Little Ice Age, glaciers in the European Alps started to shrink
but their rapid retreat has never been fully explained. It was
previously thought that it was the result of rising temperatures and
decreasing snowfall. However, records show that temperatures were
actually cooler in the Alpine region during this time than earlier in
the late 18th and early 19th century, and that snowfall levels had not changed. In theory, Alpine glaciers should have continued to grow.
The
mystery of the retreat of the Alpine glaciers has not yet been resolved
but the authors of a new study explore one possible explanation. It is
known that black carbon (BC), a component of soot which is produced by
incomplete combustion of fossil fuels and biomass, has caused melting of
snow in the Arctic, so the authors investigated whether BC was also
responsible for this glacial retreat. BC, which increased in atmospheric
concentration from the mid-19th century due to industrialisation, is
very effective at absorbing energy from sunlight. This means that when
deposited, it reduces the ability of the snow covering the glacier to
reflect sunlight, raising the surface temperature and speeding up
melting of the snow and the ice beneath. Researchers used Alpine ice
cores dating from the 18th to 20th century to
estimate the amount of additional solar energy absorbed as a result of
BC, and show that industrial emissions of this air pollutant could
explain why the glaciers started to retreat. Their results are
consistent with climate data and glacier measurements from the time. The
researchers suggest that this new understanding shows that human
influences on the Earth’s climate stretch further back than the impact
of carbon dioxide emissions alone. They also say that future studies of
glaciers should consider the effects of BC on snow and ice.
The
study adds to a growing body of research on the effects of BC and its
role in climate change. Today, one of the major human sources of the
pollutant is burning of fossil fuel, including emissions from diesel
engines. BC is also linked to damage to health and therefore action to
reduce atmospheric levels would have direct benefits for human
well-being as well as the environment.
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Source
Painter, T.H., Flanner, M.G., Kaser, G. et al. (2013). End of the Little Ice Age in the Alps forced by industrial black carbon.
Proceedings of the National Academy of Sciences. DOI: 10.1073/pnas.1302570110
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