If the climate is changing in California, it’s tempting to feel good about where we’re headed.
After all, it is hard to complain about fewer blistering-hot summer days and full reservoirs.
“I’m not really a hot-weather guy,” confessed Kelly Redmond, deputy director of the Western Regional Climate Center, a branch of the National Weather Service based in Reno. “So for me, every one of these cooler days now is a hot day prevented.”
If only it were that easy.
Yes, much of the state has been cooler than usual this summer. Many parts of the Sacramento-San Joaquin Delta even saw drizzle Wednesday morning as a mild storm pushed clouds over the region.
This was caused by the same southward-dipping jet stream that has been throwing cold, wet storms at California from the Arctic and the Gulf of Alaska, about every week or 10 days, all year long.
Is this climate change?
Climate experts sounded the oft-heard refrain that it is impossible to attribute a particular change in local weather to climate change. Weather and climate are two different concepts, they emphasize.
Try as they might to link increased carbon dioxide emissions from cars and factories to a particular weather event, the signals just aren’t clear enough yet, and the scientific tools are still too crude. “I wouldn’t conclude, on the basis of what you see out your window at any one moment, that that is what the future has in store,” Redmond said. “Nobody I’ve talked to has been able to give a really convincing explanation as to why we’ve had the relatively nice summer we’ve had so far.”
Nevertheless, scientists have long predicted that our weather will become more extreme and unpredictable with climate change. And this year could be an example.
This winter was dominated by a strong La Niña, defined by a cooling of the equatorial Pacific Ocean. The opposite of El Niño, it usually means drought in Southern California and wet conditions in Northern California.
This La Niña, however, surprised most everyone with its strength and volatility. Southern California was not dry but wet, and the rest of the state was even more wet.
Recent studies led by Michael Dettinger, an atmospheric scientist at the Scripps Institution of Oceanography in San Diego, provide plenty to ponder. The studies focus on atmospheric rivers, a phenomenon that funnels heavy tropical moisture at California and which are to blame for most of the state’s worst floods.
Such storms tend to be more common in La Niña years. And no other region of the nation, except the Southeast, can get as much rain in a single storm as California gets in an atmospheric river.
These atmospheric rivers, sometimes called “pineapple express” storms, were recognized only recently as a unique weather event and are now the focus of intense research. Such storms caused a lot of this year’s weather extremes and brought most of our winter rain and snow.
In a June study in the Journal of the American Water Resources Association, Dettinger used computer models to demonstrate that atmospheric rivers are likely to become more numerous with climate change.
They also may occur earlier in fall and later in spring.