A relatively dry El Niño winter, a warm spring that melted snow earlier and years of policies that left forests ripe for burning have contributed to the destructive wildfire that forced the evacuation of Fort McMurray in Alberta, scientists say.

Global warming may have played a role, too, although experts cautioned that it was impossible to link an individual event like this one directly to climate change.

But there is little doubt that global warming has affected the frequency and intensity of fires, and lengthened the fire season in Alberta, as it has elsewhere in North America.

“The warmer it is, the more fire there is,” said Mike Flannigan, a wildland fire expert at the University of Alberta in Edmonton. In Alberta, he said, the fire season now begins March 1, a month earlier than in the past.