We used to define fire by seasons: they varied from place to place, but there was a period of time that fires were not reliably seen before, and a date they probably wouldn’t be seen after. That is no longer the case, as the destructive fires burning this December in Southern California make clear.

The above chart shows all fires that burned over 300 acres each year from 2000 to 2017 in California, including this months’ blazes.

The future, right now: We tend to talk about extreme weather and fire events as a "glimpse into our future under climate change." But these previously-rare events are increasingly common. "If ‘unexpected’ becomes the norm, because we only talk about extreme weather, how do we change the conversation?" Jeff Rosenfeld, the editor in chief of the bulletin of the American Meteorlogical Society, asked at the American Geophysical Union's annual fall meeting on Wednesday.

The 2017 fire season was one of the worst ever seen across North America:

• At least 44 people died in a series of blazes that swept across Napa and central California.
• Fires that started in July in Montana burned for months, marking the state's second-worst season.
• British Columbia was in a state of emergency for four months.
• In the Northwest and Idaho, it wasn’t the worst season in terms of acres, but it was one of the most vigorous. The fires started so quickly and so many burned at once that resources to fight them were stretched thin.

It's only getting worse: Wildfire seasons are expected to last longer and burn hotter as climate change makes many areas warmer and dryer. "Warmer spring causes earlier snowmelt, [and] warmer summer temperatures can dry out the wood," says Jeffrey Pierce of Colorado State University.

Go deeper: Inside Climate News looks at our future with fire in a warming world.