"The northern migration of the mountain pine beetle has devastated millions of acres of forest in BC. The migration was possible because there haven't been any winters with prolonged very cold temperatures for many years."

No one is claiming that this bug problem is due solely to warming temperatures. And in North America is there was a warmer average temperature year in 1930's than compared to any year at the present period.

The guys you linked said it also had to do with forest fire prevention.
There are *probably* other factors.
And let's not forget that the same beetle is in the US, where because lower latitude would have warmer winters than compare to Canada.
There is also the possibility [which is not mentioned anywhere] that programs to re-forest after logging could have played a role in this. And it's possible that programs limiting logging could played a role in this [also not mentioned directly, but logging it is suggested as part of solution].

Additionally, temperature changes by 3 F per 1000' of elevation. Over last Century we have had a temperature increase of about 1 F. Most of this change in global temperature is reflected in warmer nites, warmer winters, but some of it is in warmer daytime temperatures. So say 3/4 of this temperature is added to decreasing average winter temperature- and at best this equal effective lowering of elevation by something like 750'- so unless this huge area is dead flat it COULD NOT be a major factor.
And obviously going a thousand mile further north is also going decrease temperature [equal or more than any from global warming].
Next, if the bug dug into the tree an few more millimeters, the difference in temperature could be wiped out because of the increase in insulated given by the tree.
Next, it is often claimed to global warming adds variability to seasonal temperature [I don't agree- but it's claimed]. With this in mind:
Beetles and Cold Weather

* Cold weather kills the mountain pine beetle. Mountain pine beetle eggs, pupae and young larve are the most susceptible to freezing temperatures.
* In the winter, temperatures must consistently be below -35 Celsius or -40 Celsius for several straight days to kill off large portions of mountain pine beetle populations.
* In the early fall or late spring, sustained temperatures of -25 Celsius can freeze mountain pine beetle populations to death.
* A sudden cold snap is more lethal in the fall, before the mountain pine beetles are able to build up their natural anti-freeze (glycerol) levels.
* Cold weather is also more effective before it snows. A deep layer of snow on the ground can help insulate mountain pine beetles in the lower part of the tree against outside temperatures.
* Wind chill affects mountain pine beetles, but is usually not sustained long enough to significantly increase winter mortality.
http://www.for.gov.bc.ca/hfp/mountain_pine_beetle/facts.htm#weather

So, "unexpected" weather can kill.
Also in Colorado:
"On Jan. 16, when the air temperature at Negron's lowest-elevation site dropped to minus 24, it was three degrees warmer just a quarter inch beneath the bark.

Three degrees may not sound like much, but it can mean the difference between survival and the "supercooling point."

That's the temperature at which water inside the larvae freezes, killing them despite a natural antifreeze the bugs produce for winter protection.

In mid-winter, the best beetle-killing scenario is an abrupt drop from relatively mild to bitterly cold temperatures, Bentz said.

If the temperature drops slowly and steadily, pine beetle larvae can adapt by gradually increasing production of glycerol, their alcohol-based antifreeze.

But if the drop is sudden and extreme, they may not have time to crank up glycerol production, she said.

"They're not going to be able to acclimate properly," she said. "There would be mortality." "
http://www.rockymountainnews.com/drmn/local/article/0,1299,DRMN_15_5356511,00.html

And finally the variation regionally- E.g. differences between BC, and other states, or even variation in seasonal temperature- between say Vancouver Island and the mainland Vancouver city area, or Okanagan area is larger than changes in global temperature.