Once we were in Seattle, it seemed only sensible to keep heading northwest, so here we are in Alaska, viewing the Hubbard Glacier from a catamaran. The glacier is 76 miles long and 7 miles wide as it enters Disenchantment Bay. The ice wall is 17 storeys high and extends a further 200 feet under the water.

(Disenchantmenr Bay, by the way, was named by the Spanish explorer Alessandro Malespina in 1722, when he discovered that his promising route to the Northwest Passage was blocked by a ...