Publication Date December 6, 2017

Did Climate Change Worsen the Southern California Fires?

United States
A ranch during the Creek Fire in the San Fernando Valley north of Los Angeles December 5, 2017. Photo: Jonathan Alcorn, Reuters

Massive wildfires are raging across Southern California, threatening thousands of homes and cultural landmarks like the Getty Museum in Los Angeles. Some of the largest fires were still barely contained by Wednesday afternoon.

It’s been an unusually bad year for the state—amid an unusually bad year for the West at large. Fires in California have destroyed more than 6,000 structures and incinerated hundreds of thousands of acres. Montana and British Columbia both also had some of their worst wildfire seasons ever.

Of course, most years are bad wildfire years now. Seven of California’s 10 largest modern wildfires have occurred in the last 14 years. (The state began keeping reliable records in 1932.) Given the scale of the blazes, and their increasing regularity, it makes sense to ask: Does global warming have anything to do with this?


Here are some of the biggest factors that are shaping the wildfires in California—and how global warming is or isn’t changing them:


A very cold U.S. East Coast

Even as the West Coast remains warm and dry, the Eastern Seaboard is settling into some of its first cold weather of the season. This pattern—a warm West, a frigid East—is known as the North American Winter Dipole.

It’s caused when the jet stream—which both ferries storms into the continent and generally divides warm air from cold air—gets especially twisted across North America. It rises far into the Canadian Northwest, keeping most of the western U.S. warm and dry; then it cascades down across the middle of the country, bringing cold air well into the U.S. Southeast.

This phenomenon prolonged California’s drought during the first part of this decade, keeping any kind of storm system offshore. It also brought the infamous “Polar Vortex” down into the continental United States

There are a number of theories about how this pattern comes to form, and most of them revolve around climate change, as Jason Samenow writes at The Washington Post.

Daniel Swain, a climate scientist at the University of California Los Angeles, argues that the ridge forms in part because the West is warming up much faster than the East. If this is the case, then scientists might expect to see the phenomenon fade in decades to come, as the East Coast catches up to the West.

But a paper published this week in Nature Communications takes another view. It finds that the disappearance of sea ice over the Arctic Ocean could change the circulation of the Pacific Ocean, encouraging the jet stream to veer north. In other words, climate change will make something like the North American Winter Dipole keep reappearing.