This contribution to a thread on The Canberra Times’ letters page appeared on Monday 29 October 2012:

Paul Pentony (Letters, October 25) trivialises the efforts of the St Roch voyages in the early 1940s. He commented on the various craft that have traversed the North West Passage (NWP) recently without mentioning that they had the benefit of satellite navigation, which simplified determining which route to follow. Also sail craft require much more open waters than motor craft as they must tack when the wind is against them.

One must remember that the St Roch was demonstrating Canadian sovereignty, letting the Inuit know that they were not forgotten during the war years and also supplying RCMP (Royal Canadian Mounted Police) outposts and that may account for some of the delay in traversing the NWP.

One must remember that Roald Amundsen sailed through the NWP in the early 1900s, also in a sailing craft without satellite aid.

The Norse expedition to investigate the extraordinary retreat of the sea ice in 1922 demonstrates beyond doubt that the amount of sea ice waxes and wanes and that the recent reduction of the sea ice is not all that unusual.

J. McKerral, Batemans Bay, NSW

In response, I wrote this, which appeared in the 2 Nov print edition:

So J. McKerral (Letters, 29 Sept) would have us believe that the collapse of Arctic sea ice cover is “not all that unusual”, because there was an expedition to investigate sea ice retreat in 1922.

This is a classic example of a tactic much favoured by climate deniers known as “cherry picking”: ignoring a huge body of evidence to focus on one tiny fragment that supports your stance.

In fact, there are hundreds of lines of evidence to show that the current loss of Arctic ice is unmatched in records going back thousands of years. See, for instance, “History of Sea Ice in the Arctic”, Polyak et al, Quaternary Science Reviews, July 2010.

Matt Andrews