1. National Snow and Ice Data Center;
http://go.nature.com/lCFnMn
2. IPCC Climate Change 2013: The Physical Science Basis (eds Stocker, T. et al.) (Cambridge Univ. Press, 2013).
3. McGarrity, J. & Gloystein, H. Northwest Passage crossed by first cargo ship, the Nordic Orion, heralding new era of Arctic commercial activity. National Post (27 September 2013);
http://go.nature.com/jyN5dU
4. Northern Sea Route Administration;
http://www.nsra.ru
5. Northern Sea Route Information Office;
http://www.Arctic-lio.com/