OSLO, Sep. 18, 2012 (Reuters) — Local pollution in the Arctic from shipping and oil and gas industries, which have expanded in the region due to a thawing of sea ice caused by global warming, could further accelerate that thaw, experts say. The United Nations Environment Program (UNEP) said there was an urgent need to calculate risks of local pollutants such as soot, or "black carbon", in the Arctic. Soot darkens ice, making it soak up more of the sun's heat and quickening a melt. Companies such as Shell, which this week gave up a push to find oil this...