SAN FRANCISCO—Frequent landslides triggered by global warming will threaten safe operation of the proposed $7-billion Mackenzie Valley gas pipeline, a Canadian permafrost expert warned here yesterday.

The pipeline, which has already cost $200 million in preliminary studies, is intended to carry natural gas from the Mackenzie delta south more than 1,200 kilometres to northwestern Alberta.

The proposal still faces a federal environmental impact review before construction can begin in 2006 to finish by the end of the decade.

But permafrost expert Antoni Lewkowicz cautioned scientists here that rapid warming of the Arctic from global climate change could spell trouble for the pipeline.

“This needs to be looked at in the environmental review and it wasn’t fully covered in the original outline,” the University of Ottawa geography professor said in an interview.

Lewkowicz told the annual meeting of the American Geophysical Union the combination of higher temperatures and prolonged summer sunshine in the Arctic is melting vast swaths of permafrost — ground normally frozen for much or all of the year — and triggering massive landslides on a regular basis.

Since 1987 his research, supported by the federal government, has extensively documented increasing landslides at three locations on northern Ellesmere Island. Similar conditions exist along the pipeline route through the Mackenzie Valley, Lewkowicz said.

“If one of these landslides went across the pipeline, it would leave it unsupported. That could cause problems,” said Lewkowicz, who worked on pipeline engineering in the private sector.

The researcher said these “detachment” slides take place when ice down inside the permafrost is melted by the double whammy of heat and sunshine.

“The mass of soil above slides on this melted ice, a lot like someone slipping on an icy sidewalk that has water on the surface,” he told a news conference here.

Near Eureka on Ellesmere Island such slides are typically 150 metres wide, a half-metre deep and more than half a kilometre long. “You can’t get that much material to move unless it is really wet on the bottom,” Lewkowicz said.

Yet higher summer temperatures in the Arctic in the last two decades from global climate change are making the conditions for such potentially destructive slides much more common. Seven days of 24-hour sunshine combined with air temperatures of 7 C will trigger a slide if ice conditions inside the soil are right, Lewkowicz told the geophysical meeting.

So will air temperatures of 11 C and 17 hours of sunshine and other equivalent conditions.

Lewkowicz’s remarks were just one of several warnings from an international panel of scientists about potential dangers from accelerated melting in the Arctic and other northern regions because of global warming. Other findings included:

* More than 30 major rockfalls occurred in the Alps in 2003 when Europe suffered through record summer temperatures. British scientist Charles Harris said the heat melted the ice that cemented rocks together at high altitudes that usually stayed frozen year-round.

* Chinese engineers are laying a metre-thick insulation bed of crushed stone beneath 550 kilometres of railway track where it crosses permafrost on the Tibetan plateau.

* Researchers with the Yukon Geological Survey, collaborating with Lewkowicz, this year identified heat-induced weakening of a glacier as the most probable trigger for a powerful 1995 landslide in the remote Kluane Ranges that shoved a bus-sized boulder almost two kilometres.

“Imagine what could have happened if that had been one of the glaciers in the Rockies that’s near a town or highway,” said Crystal Huscroft, a professor at the University College of the Cariboo in Kamloops, B.C.