Is climate change what’s wreaking weather havoc?
SAN FRANCISCO — When San Francisco hit 103 degrees in June 2000, a new high after more than a century of record-keeping, the forces of global warming were likely at work. But scientists weren’t ready to go there.
Climate change had barely become a household term, and teasing out its complex role in single events that are largely at the mercy of natural weather variability was unthinkable.
Seventeen years later, as the Bay Area recovers from another round of record heat that pushed San Francisco to a new pinnacle of 106 degrees — and as a deadly lineup of storms pounds the southern United States and the Caribbean — climate researchers are making these critical but elusive connections.
There’s still no simple answer to the question, “Was that hurricane caused by climate change?” But scientists can now often say whether an event was more likely, and more severe, due to the warming planet.
A team of experts at Lawrence Berkeley National Laboratory, among the foremost pioneers of the evolving science of extreme event attribution, estimated that human-caused climate change probably raised temperatures in California by as much as 4 degrees at the start of this month.
Similar accounting has been done for the California drought and strings of wildfires across the West, as well as the catastrophic hurricanes Harvey and Irma, whose devastation is still unfolding.
The ability to quantify the influence of global warming on a single event is important not only because it highlights the threat of climate change, but because it could help communities understand exactly what they’re up against. Those seeking stronger responses to global warming have been frustrated by the information gap.
While scientists still can’t say that climate change caused any one weather system, studies have found that past heat waves in both the U.S. and abroad were so unlikely in the absence of global warming that there was little other explanation for what drove them.
“Scientifically we’ve come a long way,” said Noah Diffenbaugh, an Earth system scientist at Stanford University who is among those tracking the fingerprints of climate change on weather.
“Around 2000 or so, you mostly would have heard from the scientific community that we can’t