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Global warming's role in California's wildfires

Governor Brown
Governor Brown 13:26

What's causing the massive California wildfires that have scorched an area the size of three major cities and cost the largest state more than $180 billion? The obvious answers from fire officials: Santa Ana winds of up to 80 miles per hour swooping down and westward from the Southern California mountains, three years of the worst drought in state history and uncleared tinderbox brush that fuels the fire.

But is there a bigger answer? Is this the handiwork of global warming and climate change that will give rise to next year's California apocalypse? Gov. Jerry Brown says yes, and he places the blame on Donald Trump, saying the president has "no fear of the Lord." Brown calls Mr. Trump's denial of climate change and pulling the US out of the Paris Accord "evil." Signed by 195 nations, the accord is meant to reduce the carbon emissions most scientists believe are turning up earth's temperature.

Is Brown, right? Is there any objective standard measurement? The Actuaries Climate Index (ACI) probably comes close. Four actuarial societies in North America developed this index to measure the frequency of "extreme climate events" by using the period from 1961 to 1990 as its baseline and then measuring changes in subsequent extreme events.

Southern California wildfires 02:33

The actuaries don't take a political stand. Their job is simply to measure risk for the insurance industry. And American insurance companies have never taken a position on climate change or global warming.

The six yardsticks the ACI uses to measure extremes are high and low temperatures, heavy rainfall and drought (consecutive dry days), and high winds and sea levels. Since the index looks at measurable data from past seasons, its most recent report dates back to February. But the index already shows "big changes" in the weather and the risk it creates, said Doug Collins, chair of the ACI Working Group.

"Elevated values in temperature are helping drive the ACI higher, particularly in the Southwest, which includes Arizona, California, Colorado, Nevada, New Mexico and Utah," said Collins. "These regions have experienced five seasons in the past five years with high temperature index values."

The Southwest hasn't seen these kinds of elevated temperatures more than three times in the prior 50 years, he said. The earliest data these actuaries had to work with dates back to the 1960s, Collins said, but the extreme temperatures started to spike in the 1980s and haven't really let up since.

While the long-lasting California drought obviously factors into these fires, along with the mountain winds blowing down on the Los Angeles-San Diego area, Collins said heat is actually the main long-term factor behind what's happening in the Southwest. "That surprised us," he said. "We thought it was the drought and wind, but that's an ongoing issue in California. We found that brush fires are more strongly correlated with high temperatures."

A changing climate 03:16

To compile their ACI, the actuaries chose to focus on the "extremes" and how often they occur and not on average temperatures, which are easily accessible going back at least 100 years. The temperature extremes also affect other pieces of the ACI, such as sea level.

When asked if we're looking at a new normal -- a normal of extremes, Collins said: "It appears that way."

In his attack on President Trump, Brown pointed out that California, which now has an economy larger than that of France, was curbing the burning of fossil fuels that pump carbon into the atmosphere. Carbon emissions are often seen as one of the primary causes of global warming. The governor even posed next to a 62-acre solar panel farm and pointed to the state's "cap and trade" law, which allows energy producers to buy credits from environmentalists who plant trees and repair streams to help absorb carbon emissions.

But while Brown appears to be taking on both Trump and global warming singlehandedly, Collins said that would be inadequate to the task. "This is something that needs to be addressed on a global level," he said. "It can't be dealt with by a single state or even a single country."

To view the ACI data, which has been downloaded 1,700 times, go to

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