It's official: 2017 is the deadliest and most destructive year on record for wildfires in California. Dry conditions, high temperatures, roaring winds and bone-dry trees and brush are all factors responsible for the devastation. But one underlying question is how much of a role has climate change played?

"There is no singular cause for any real significant event," said Daniel Swain, a climate scientist at UCLA.

"It’s usually a confluence of factors that are important. And in a lot of cases, global warming definitely plays a role and is one of those factors."

Gov. Jerry Brown certainly seems to think climate change is a major contributor.

"This is the new normal," Brown warned Saturday. "We're about ready to have firefighting at Christmas. This is very odd and unusual."

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Let's break down each of the factors that have contributed to this year's destructive wildfire season to assess whether climate change looms in the background.

[audio src="https://www.kqed.org/.stream/anon/radio/tcr/2017/12/FireClimateChangeMargolis171211.mp3" Image="https://ww2.kqed.org/news/wp-content/uploads/sites/10/2017/12/ThomasFirePlumeISS-1920x1235.jpg" Title="Southern California Is Burning -- Is Climate Change to Blame?" program="The California Report"]

Winds

"In terms of these really fast-moving and destructive wildfires that tend to be a threat to life and property, there’s almost always some sort of strong winds involved," Swain said. "Those winds can cause fires to move quickly, to jump over barriers over freeways and jump from house to house and move out of the forest, and out of the dry brush into regions where people actually live."

Neither the destructive Northern California fires earlier this fall nor the massive Thomas Fire currently rampaging through Ventura County would've spread as quickly without the help of strong, dry winds. Southern California has Santa Ana Winds to blame -- and the current wind event is both stronger and longer than normal.

According to the National Weather Service, Santa Ana winds gusted up to 60 to 70 miles per hour on Thursday. Usually, the winds gust between 40 to 50 miles per hour. Santa Ana events generally last two to three days -- the current event has lasted for more than five. And this time, they're also especially dry, with humidity levels around 1 to 2 percent in some places of the region.

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The stronger and longer-lasting winds are a result of a particularly strong, particularly cold high pressure ridge sitting east of the rockies. As the wind travels from that area of high pressure across the Great Basin towards areas of low pressure along California's coast, the wind speeds up, compresses and slams into Southern California.

The question of whether the intensity and duration of the current Santa Ana winds have been impacted by climate change is still up for debate, according to Alex Hall, director of the Center for Climate Science at UCLA.

Hall said there's research supporting both the idea that the Santa Anas will increase in strength and frequency, as well as decrease, as the climate warms. Part of the difficulty of anticipating what'll happen to the Santa Anas is that the modeling scientists use to anticipate changes around the world struggles to simulate regional circulation patterns, Hall said. That includes the Santa Anas and ridges of high pressure off the coast of California that are associated with a lack of rain.

But Hall's confident that the relative humidity of the Santa Anas will fall as things get warmer due to climate change, which doesn't bode well for fire risk as the dryness of the winds is a major contributing factor to the spreading of wildfires.

Precipitation

A lack of rain is another reason these major wildfires have spread so quickly.

"In a warmer climate, you have a greater contrast between wet and dry," said Hall. "In the future, we anticipate increased variability in precipitation. So, more precipitation in wet years and less in dry years."

Between 2012 - 2016 California was riddled with extreme drought. Droughts in and of themselves aren't uncommon, but the our most recent one was likely made worse by human caused climate change, according to a paper written by A. Park Williams, a climate scientist at Columbia University.

Although this past winter felt particularly wet, that was likely because it followed years of drought. In reality, we experienced an average to slightly above-average amount of rain, mostly in January and February. For most of California, drought conditions were alleviated. However for Ventura County, the location of the Thomas Fire, a moderate drought remains.

It's widely accepted that along with climate change we'll experience extreme dry periods, punctuated by short, extreme periods of precipitation.

Following our deluge of rain and snow earlier this year, things have since been hot and dry.

“For the last six months say, we’re running both above average temperature-wise and below average precipitation-wise here in Southern California," said Swain. "In the short term there has been a trend towards a lot more dry years in Southern California. The question is how sustained is that going to be."

There's been no rain in Los Angeles so far this season.

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The current lack of rain can be blamed on a ridge of high pressure sitting off the west coast of North America, blocking storms from passing over our state.

“Hopefully this’ll be a temporary feature, maybe it’ll stick around for just a couple of weeks," said Brad Rippey, agriculture meteorologist with the USDA. "But man, I sure hope it’s not going to stick around for the entire winter."

The ridge is similar to the one responsible for the recent drought, which was coined the Ridiculously Resilient Ridge by Swain. That weather pattern was an anomaly, in part, because of the length of time it stuck around.

There's ample research to support the theory that warming in the western tropical Pacific is associated with the arrival of rain-blocking ridges, an area seems to be warming faster than the other parts of the ocean. However, why that's occurring is up for debate.

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"The ocean isn’t warming at the same rate everywhere," said Swain. "And whether that differential rate of warming from one place to another is itself an expression of global warming, or if that’s just sort of a little bit of random noise superimposed on top of the long term warming trend I think remains to be seen."

A recent study out of the Lawrence Livermore National Laboratory theorizes that the melting of Arctic sea-ice could also contribute to the formation of ridges off the West Coast. Exacerbated by global warming, it's thought that the Arctic could be ice-free during the summer months.

According to the study, "low Arctic sea-ice increases the likelihood of drier California, but does not result in drier conditions over California every single year. On average, when considering the 20-year mean, there is a 10 to 15 [percent] decrease in California’s rainfall."

"I think we should trust that sea ice is inducing the ridge," said Ivana Cvijanovic, author of the study. "The question is, what are other factors too? Do they increase impact of sea ice or offset it?"

“That part is really compelling, but it’s still going to be debated for a bit,” said Williams when asked about the study.

Fuel Load

None of these fires would've happened if there wasn't anything to burn -- and this year Southern California is flush with fuel.

"There was enough rain to promote some grass and brush growth last winter," Rippey said.

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That grass has dried out since then, not only from a lack of rain, but also because of the heat during our record setting summer and fall.

As temperatures rise, so does the speed at which moisture evaporates from the soil.

Combine the higher temperatures and a lack of rain with hillsides covered in brush and you've got the perfect recipe for rapidly spreading fires.

“So, this confluence of factors, of the really strong wind event this week, of these really hot, record hot conditions in the autumn and parts of the summer months as well, and then this lack of rain this fall," said Swain.

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"Those three things right now would’ve contributed to the fires in Southern California being as bad as they are."

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