By Paul Rosenberg, Senior Editor
The Thomas Fire became the largest recorded wildfire in California history this week, the first of a far-flung splatter of fires triggered by Santa Ana winds starting on Dec. 4. The Creek, Rye and Little Mountain fires erupted the next day, followed by the Skirball fire on Dec. 6, and Liberty and Lilac fires on Dec. 7.
Ten years ago, Random Lengths News wrote about a similar outbreak of Southland fires, framed in terms of global warming, but we’re no longer an isolated voice making the connection. The UCLA Newsroom published a story UCLA experts explain why California is burning in December, almost all of which was global-warming-related in some way.
“The temperature extremes — a record-warm summer and autumn — are exactly what we expect to occur given climate change, and there’s evidence that autumn and spring are likely to become even drier, even if our annual precipitation doesn’t change much,” said Daniel Swain, a climate scientist quoted in the story.
One big-picture way to grasp what’s happening begins with understanding global warming as doing two things: first, raising temperatures broadly, and second, raising the amount of energy flowing through the global ecosystem, increasing its turbulence and expanding the range of extreme states on multiple scales of time and geography.
One time scale is that of multi-decade megadroughts, first discovered by Columbia University climate modeler Richard Seager, who we interviewed in 2007. He identified a 4th century when a series of megadroughts that affected large areas of the West. The transition to this sort of climate was already under way, he told us, well before the past four years of severe drought followed by two years of drenching rains. Medieval megadroughts were occasionally punctuated by years like that, without ending as a result. So we could still be in the midst of the first megadrought of the modern era.
In fact, the two-year cycle of floods followed by drought that we’re living through now—at least so far—is another level on which extreme states produced by climate change can be observed. “Last year’s stormy and wet winter, coupled with this year’s record-breaking high temperatures, and our current dry winter conditions, mean that we are extremely susceptible to fires — and this problem is going to continue and get worse,” said paleoclimatologist Aradhna Tripati in the UCLA story, neatly summarizing how this two-year cycle and the underlying warming trend combine to raise the fire threat ever higher.
On the other extreme, daily cycles are growing more intense as well—exemplified by extremely low humidity and strengthening Santa Ana winds. There are also cyclic patterns in between. One, first noticed by Swain in 2013, is the “Ridiculously Resilient Ridge,” a region of unusually high atmospheric pressure pushing the Pacific jet stream to the north of California, resulting in very dry conditions.
The ridge has returned repeatedly since, and is now seen in its larger context, linked with low pressure and outbreaks of very cold, Arctic air across the eastern United States, such as the “Snowmageddon” and “Snowpocalypse” snowstorms. One study showed a sustained upward trend in the number of days typified by this “dipole” condition. Thus, while climate deniers point to snow as disproof of global warming, scientists are gaining a clearer picture of how it’s exactly the opposite — and intimately tied to the very different extreme weather (and consequences) we’re living through in Southern California.