Derek Neary
Northern News Services

Fort Simpson (Apr 19/02) - April has been a cool month so far.

Temperatures have been averaging seven to nine degrees below normal, so closure of the ice bridges, which is followed by break-up, could come a little later than usual.

But, in the bigger picture, is global warming causing break-up to occur earlier and freeze-up to occur later?

A report published in the journal Science last year revealed that ice on the Tenana River in Alaska breaks up five days earlier on average than it did 84 years ago.

In the community of Nenana, the same tripod competition as is customary in Fort Simpson has been used to compile the data for the Tenana River.

Unfortunately, the situation in Fort Simpson isn't so clear cut. First of all, the statistics have only been collected since the 1960s. Secondly, the tripod is placed down-river from the confluence of the Mackenzie and Liard rivers. Although the Liard almost always lets go first, the years when the Mackenzie goes first could skew the data, hydrometric technician Gerry Wright suggested.

Hydrometric supervisor Roger Pilling said there's been no indication of a significant change over the past 25 years.

"The first week I was here, (former Water Surveys employee) Pat Wood told me that break-up happens the first week of May, and it still does," said Pilling.

However, if you flip the calendar back a few months, the ice bridge at Fort Providence didn't open to light traffic until Jan. 22 this year, close to the latest it has ever opened. By comparison that same ice crossing opened on Nov. 28 during the winter of 1990-91.

It was regularly ready by late November or early December 10 to 15 years ago, according to Art Barnes, superintendent of transportation for the South Slave.

"I don't know whether it's enough to establish a trend, but certainly the winters from a personal level seem to be kinder than they were in the past ... and we've seen that in the river freeze-ups, they're just staying open longer and longer," Barnes said. "Whether it's global warming, who knows?"