From Prof Robert H. Wade.

Sir, In my article “A warmer Arctic needs shipping rules” (January 16) I argued that the Arctic Ocean is opening for shipping and resource extraction much faster than was expected a few years ago. Michael Bell (Letters, January 24) raises doubts. He says a vessel on the Northern Sea route, just above Russia, would have to maintain an average speed of about 16 knots to match the China-Europe journey time via Suez, “an impossible feat until there is no Arctic ice whatsoever”.