Climate Change in the Arctic - The Changing Arctic Environment: The Arctic Messenger - page 291

BC consists of small dark particles that result from the incomplete combustion of bio-
mass and fossil fuels. The most common sources are diesel cars and trucks, wood-burning
stoves, forest fires and agricultural open burning. It can influence the climate in at least
two ways. Firstly, BC absorbs incoming and reflected solar radiation and therefore warms
its immediate environment. This direct radiative forcing by BC is important globally and
regionally. (It ranks third globally behind carbon dioxide and methane.) Secondly, if depos-
ited on snow and ice, BC directly decreases the surface albedo and increases the amount of
heat absorbed. We are already familiar with the consequences. Melting is accelerated and
the darker tundra and sea surfaces exposed result in a continuing positive snow/ice albedo
feedback. Once deposited on a glacier or ice sheet, BC can remain for years before it is re-
moved by surface runoff or incorporated into glacial ice. Therefore, it can exert its impact
on albedo reductions over more than one seasonal melt cycle. However, nothing is ever
simple. Some important aerosols, such as sulphates, are co-emitted with BC and can be
strong negative climate forcers. Without them, we would currently be experiencing greater
warming!
Climate models show that BC contributes to climate warming globally. However, the
intensity varies regionally because of its relatively short residence time in the atmosphere
and because of regional patterns of atmospheric circulation. Therefore, BC originating
from Arctic and non-Arctic sources contributes to Arctic warming. The AMAP team con-
cluded that the BC snow/ice radiative forcing per unit of BC emitted increases with latitude
and is larger for the Arctic Council countries than for the rest of the world. As a result, the
Nordic countries are associated with the largest forcings per unit of BC emission due to
those emissions occurring at higher latitudes and therefore closer to the areas of Arctic de-
position. There is some question as to the overall net effect of a given BC source to global
warming, but as far as warming in the Arctic is concerned, there seems to be little doubt.
BC can be 680 times more effective as a climate forcer than CO 2 locally in the Arctic. A
study published in 2007 attributed about a 0.24°C temperature increase to BC-derived ra-
diative forcing within the Arctic atmosphere. For the deposition of BC on highly reflective
snow and ice surfaces, the attributed surface temperature increase was about 0.56°C.