Heat, storms expected to grow more frequent
It may not be the biblical end of times, but the searing heat and humidity, rain, thunder and lightning thrashing California could be the beginning of the end of the region’s dry Mediterranean climate and a prelude of more surprises to come, scientists said Monday.
The strange and, in many ways, unprecedented weather fits in with the pattern climate scientists have been predicting for 30 years if nothing were done to stop carbon emissions.
“We’ve gotten to the point where, when it comes to extreme heat waves, there is almost always a human fingerprint on them now,” said Daniel Swain, a climate scientist at UCLA and the National Center for Atmospheric Research,
who issued a warning last week about the weird weather system barreling down on California. “Every study we’ve done says that climate change is making heat waves worse and more frequent.”
Record or nearrecord temperatures combined with periodic thunder storms are expected to continue through Wednesday night, including in San Francisco and other coastal areas unaccustomed to tropical temperatures, let alone bolts of lightning.
Heat advisories and excessive heat warnings have been issued by the National Weather Service across the region, throughout the state and over the entire southwestern United States.
Nothing this extreme has been recorded by meteorologists in the Bay
Area in recent memory, but that doesn’t mean events like this weren’t expected, said Noah Diffenbaugh, a climate and earth systems scientist at Stanford University. His research laboratory found that increasingly brutal spells of heat and drought as well as rain and snow are up to five times as likely to occur over large stretches of the planet in coming decades as global temperatures continue to climb.
“We found that global warming has increased the odds of record hot daily temperatures over more than 80% of the globe,” including in California, Diffenbaugh said Monday. “The southwestern U.S. is one of the areas where we find a strong influence of global warming on record daily hot temperatures.”
It is impossible to attribute any single weather event to global warming because there is no way of knowing whether it would have happened in the absence of climate change. That’s why researchers focus their studies on determining probabilities.
Diffenbaugh’s research team has determined, for instance, that recordsetting heat would be expected across 50% to 90% of North America if global warming were limited to an average of 3.6 degrees above preindustrial levels.
Climate change has so far increased global temperatures about 1.8 degrees above preindustrial levels, he said, so it could take decades before such widespread heating occurs. Still, Diffenbaugh’s published studies suggest that the amount of global warming that has already occurred has more than doubled the probability of the hottest day of the year being exceeded in the western United States.
“Global warming has at least doubled the odds throughout the region and, in some areas, it has tripled the odds,” he said. “These kinds of heat waves are a feature of the climate that we are now living with as a result of the global warming that has already happened.”
Warmer overnight temperatures, like the balmy nights the Bay Area is now experiencing, were also predicted by climate scientists. Scientists have shown that warmer air means more evaporation and greater surface drying, as well as more moisture in the atmosphere and bigger storms.
The blistering heat in the Bay Area is being held in place by a ridge of high pressure, but meteorologists say there are other influences. Humid air from the remnants of Hurricane Elida in the Pacific also moved over California, and moisture from Tropical Storm Fausto, a thousand miles south of San Francisco, has also pushed into the area.
All of that created a convection system that caused thunder and lightning storms the likes of which at least one Northern California meteorologist said he hasn’t seen in more than four decades.
Thunderstorms like the one that struck the Bay Area over the weekend are highly unusual for this time of year. Diffenbaugh said, however, that it is harder to blame the thunder and lightning on global warming. Still, he said, there is strong theoretical evidence of that for most of the U.S. as the average global temperature rises, Diffenbaugh said.
It is particularly hard to predict how current or future global warming is likely to influence weather in the Bay Area because the ocean, mountains and topography create so many microclimates, Diffenbaugh said.
But the current hot, humid weather may be giving us a glimpse. Heat waves like this one, according to all the evidence, are likely to be more common from now on.
“Once the event comes to completion, we’ll be able to assess where it fits historically,” he said. “But it’s very clear that these are conditions that have been predicted as the globe heats up.”