A hammer started the largest wildfire in California history

410,203 acres burned.

Last summer, the Ranch Fire -- which was part of a greater complex of fires -- ripped through Northern California, smashing the previous, short-lived record for the largest wildfire in state history by some 128,000 acres.

And it all started because a hammer, used to drive a stake into the ground, tossed either sparks or bits of hot metal onto the parched land. The Golden State's fire protection agency, Cal Fire, revealed the historic conflagration's cause Thursday and posted the incident report online.

That the use of a simple tool is responsible for igniting the Ranch Fire highlights how extreme fire conditions were last year, and how the Western U.S. overall is experiencing a significant hike in conditions ripe for flames. A warmer climate means more dry, flame-susceptible vegetation.

"Now we’re in a climatic period where the fire seasons are getting longer and deeper, hotter and drier, and maybe even windier," John Bailey, a fire ecologist at Oregon State University told Mashable in November, following a number of destructive California blazes.

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Fires are growing more severe in the Northern Hemisphere, research shows. Wildfires in the U.S. are now burning for weeks longer than they were in the 1970s, and they're burning twice as much land than were in the 1990s.

"Fires themselves are also getting harder to fight," said Valerie Trouet, a fire researcher at the University of Arizona. "With so much fuel on the landscape, they’re just higher intensity fires. They’re risky and difficult to control, which contributes to them burning for longer."

The Ranch Fire is representative of California's new fire regime, in which just a few sparks can ignite a historic blaze (it's rare for a hammer to start a fire). As fire experts pointed out before the blaze began, hot temperatures and heat waves had parched much of Northern California's vegetation to near-record levels of dryness, turning the land into fire-ready kindling. 

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Wildfires never have a single cause, but are the confluence of climate, hot and windy weather, and human activity, which includes gross forest mismanagement. But the climate knob has been dialed up.

In the case of the Ranch Fire, the sparks or hot metal that landed in tinder-like grass stoked a fire just 2 feet by 2 feet in size on July 27, 2018.

Then, it exploded.