The unseasonably strong Santa Ana winds that have pounded southern California during the past two days have left hundreds of thousands of residents without power, not to mention closed schools and businesses. Many counties are on emergency footing and even Griffith Park, one of the nation’s largest urban parks, has closed as crews struggle to clear fallen trees and debris away from power lines and off roads.
But the extreme winds – the strongest in at least a decade – have also raised the familiar question: Are they one more indication of global warming's larger trend toward extreme weather?
The answer is no. Mostly.
On one hand, most scientists agree that “the extremity and magnitude of extreme weather events has been trending upwards over the past 60 years,” says John Plavan, CEO of EarthRisk Technologies, a San Diego firm that models weather-related risks for energy clients.
Yet the same climate changes that are driving certain extreme weather events will also soften others, says David Easterling of the National Climatic Data Center, a part of the National Oceanic and Atmospheric Administration in Asheville, N.C.
The Santa Ana winds could be an example of that. The annual winds that sweep through southern California from November through April are caused by high-pressure systems sweeping cool air from the Great Basin southwest into the Los Angeles Basin. As the winds descend the San Gabriel Mountains, they heat rapidly, resulting in the hot, strong winds.
But as climate changes raise temperatures in the Great Basin, the engine driving the Santa Anas could dissipate, “leading to less extreme Santa Anas in the future.”
In another 25 to 50 years, those winds will significantly decline, says Dr. Easterling.
But he is quick to point out that other extreme events tied to climate change – such as heat waves and precipitation – will accelerate. “If you are in a flood-plain area, more insurance down the line might not be a bad idea,” he adds.
Extreme weather events are an important signal bell for the rest of society, even if they're not tied to climate change, says Villanova University assistant professor of geography and the environment Keith Henderson.
“Extreme events naturally attract a lot of attention, especially from the public,” he writes in an e-mail. “The impact of extreme events, both real and perceived, makes it important that we study climate variability as much as climate change. We need to better understand the frequency, intensity, and patterns of extremes to better understand how weather and climate affect society.”
The need for longer-term forecasting models is growing, adds Mr. Plavan. While forecasting specific events is difficult, using decades of previous years' data can help project probabilities.
For instance, if experts can produce data that show a city is 40 percent more likely to have a major heat wave over a certain time frame, Plavan says, “then the city can plan from a longer-range perspective, rather than doing the equivalent of buying a snow shovel no matter the cost when the heavy snow starts to fall.”