Pushed for time and strapped for cash, the engineers laid eight miles of track straight up Big Hill, at a gradient more than twice the safe maximum.

BBC: The wonders of Canada by rail

Increased evaporation from the exposed sea should also mean more snowfall to compensate for the ice cap's losses (though together with rapid erosion at the margins this could increase the gradient of the ice cap, making it less stable.) But this is small consolation for another big fear: rapid thawing of the Arctic permafrost.

ECONOMIST: The science