Wildfires from the Oregon border to Los Angeles. Temperatures hitting 100 degrees in San Francisco, and higher in Sacramento, capping off the hottest summer in California history.
Not to mention two of the most ferocious hurricanes ever recorded.
It has to be climate change, right?
The answer is a little more complicated than you might think.
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As Hurricane Irma prepared to strike the Florida coast and millions of acres continued to burn in the West, climatologists said it was overly simplistic to blame global warming for the flurry of chaotic weather afflicting portions of the United States. Wildfires, heat waves and hurricanes are common this time of year.
“This is hurricane and heat wave season,” said Bill Patzert, a climatologist at NASA’s Jet Propulsion Laboratory near Pasadena.
Nonetheless, Patzert and other experts said the Earth’s climate truly is getting warmer, and that phenomenon is responsible for increasing the intensity and frequency of extreme weather events.
Take Hurricane Harvey, which dumped the Houston area with 50 inches of rain in barely a day. Warmer temperatures, likely caused by climate change, filled the atmosphere over Houston with more moisture and made the hurricane wetter than it would have been, said Paul Ullrich, a climate modeling expert at UC Davis.
“There are fingerprints of climate change,” Ullrich said.
Climate change skeptics, including top officials in the Trump administration, have sidestepped assertions by environmentalists, climatologists and others that climate change has been responsible for the latest spell of weather. Interviewed by right-wing media outlet Breitbart about Hurricane Harvey last week, Scott Pruitt, administrator of the Environmental Protection Agency, said it was “opportunistic” and “misplaced” to link the Houston disaster with climate change. It was more important, he said, to “focus upon the needs of people.”
Climatologists, however, said it’s undeniable that climate change is making normal weather patterns more extreme. It’s just that the impact often tends to be at the margins.
Ullrich said climate change likely increased temperatures by 1 degree or so in Northern California last week. But he said Northern Californians would have sweltered with or without global warming.
“You can’t say there wouldn’t have been a heat wave if there hadn’t been climate change,” he said.
Last week’s heat wave sent temperatures past 100 degrees at San Francisco International Airport and 110 degrees in portions of the Sacramento Valley. It was the fitting end to the hottest summer in California history.
The average statewide temperature was 73.7 degrees from June through August, breaking the record set in 2006 by about a half a degree, according to the Western Regional Climate Center in Reno. This year’s summertime average was 3.2 degrees above the historical average.
In fact, every summer in this century has seen above average temperatures, except 2010 and 2011, according to the center.
State climatologist Michael Anderson, who works for the Department of Water Resources, said Californians should start getting used to this kind of weather.
“We’ve had hot summers in the past, but as the world warms you spend more time above certain (temperature) thresholds,” Anderson said. “There’s no one event that’s going to be a flashing sign saying, ‘Climate change did this.’ It’s just the background upon which these events start playing out. We’re in a warmer world than we were back in, say, 1991.”
California’s hottest regions usually get a respite from blast-furnace summers during the nights, but the warming climate is gradually making evenings hotter, Anderson said.
“That changes the nature of the heat waves from the standpoint that you don’t get the hours of relief,” Anderson said.
Scientists said climate change might have worsened this year’s wildfires, which blanketed portions of the state with smoke. Some of the largest fires threatening homes last week in California have been mostly contained, including the Ponderosa Fire in Butte County and the La Tuna Fire in Los Angeles. But there are still approximately 1.4 million acres burning throughout the West, according to the National Interagency Fire Center, adding to one of the most severe fire seasons on record.
So far wildfires have consumed 7.8 million acres this year, the center reported. That compares with 4.2 million acres at this point last year, and an annual average of 5.5 million acres over the past decade.
“It’s very difficult to link a specific event to climate change,” said Timothy Brown, director of the climate center in Reno. “But again, having a warm, dry summer in these regions certainly puts the potential for a lot of fires in play.”