What's causing the unprecedented wildfires spreading across Canada is a mix of things.
Lightning strikes likely ignited some of them, but it's unseasonable weather that's helped the spread.
Climate change may increase both lightning strikes and the risk of severe wildfires in the future.
Lightning strikes and unseasonably warm weather are to blame for the fires in Canada, experts said.
Over the last six weeks wildfires have spread across Canada, burning nearly 10 million acres. These active wildfires are burning across central and eastern Canada, focused in Ontario and Quebec, and they have generated a cloud of smoke that has wafted down to the eastern US, polluting the air and disrupting airfare.
Forest fires in Canada are a general occurrence, particularly in the west. But it is "unusual" to see them burn on both coasts at the same time, Michael Norton, an official with Canada's Natural Resources Ministry, told Reuters.
"At this time of the year, fires usually occur only on one side of the country at a time, most often that being in the west," he said.
What started the fires?
That said, the fires in Quebec in the east were likely ignited "within a short window after a big lightning event," said Ellen Whitman, a forest fire research scientist who works for Natural Resources Canada in the Canadian Forest Service, to the Halifax Explainer.
"Generally in Canada, lighting-caused fires are about half of our ignitions, but they make up the majority of area burned because they are ignited in places where there are no people nearby to notice them, so they get detected less quickly," Whitman said.
Dry weather pushed the fires forward
Kent Moore, professor of physics at the University of Toronto told Yahoo News! Canada spring fires in Nova Scotia are usually easier to extinguish, as the soil is still wet.
This year, however, spring has come early, and the soil has remained drier than usual, allowing the fire to keep smoldering deep underground, Moore said.
"Those are much more difficult to put out because you have to dig up the dirt to get to the fire," Moore said. "That's typically what you'd find in the summer fire season when things tend to be drier."
Climate change is likely making the fire fiercer
For Moore, climate change can't take all the blame for the fires on the east coast. It may come down to season variability.
"There's just natural variability," he said. "Some springs are dry and some springs are wet."
That's not to say climate change doesn't have a part to play, however.
"The fires season is also lasting longer now because of climate change. Spring is coming weeks earlier and fall is coming weeks later. More time for the fires and grasslands to burn," Edward Struzik, a fellow at Queen's Institute for Energy and Environmental Policy at Queen's University in Canada told CBS News.
The igniter itself — lightning — is more common due to climate change, Struzik said.
"Most fires in the boreal forest of northern Canada are started by lightning. A one-degree Celsius increase in temperature amounts to about 12% more lightning. So the warmer it gets as the climate heats up, the more triggers there are for fires to burn," said Edward Struzik, per CBS News.
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