The effort was spearheaded by Gov. Jerry Brown to move the fight against global warming beyond the national commitments made in Paris nearly three years ago.
"Look, it's up to you and it's up to me and tens of millions of other people to get it together to roll back the forces of carbonization," says Brown in a promotional video for the summit.
It is likely to be Brown's last big climate event before he leaves office next year, and it comes at a time when many scientists agree that time is running out for a major counteroffensive against global warming, which Brown has repeatedly called an "existential threat."
"We are not prepared," says Inez Fung, an atmospheric scientist at UC Berkeley, who can see the accelerated effects of a warming planet all around her, from raging wildfires in the western U.S. to death-dealing floods in India.
"Thirty years ago we predicted it in the models," she says, "and now I'm feeling it. I'm experiencing it."
Across the U.S., the average temperature has risen almost 2 degrees Fahrenheit since the start of the 20th Century. In California, the heat has been turned up unevenly, with portions of the state warming over the same period by anywhere from one, to nearly three degrees. (The South Coast of California has experienced the biggest rise.)
And because the global oven was first fired up with the burning of fossil fuels more than 200 years ago, scientists say a certain amount of future warming is already "baked in."
"We released enough carbon dioxide to continue warming the climate for several centuries to come," observes Bill Collins, who directs climate and ecological science at Lawrence Berkeley National Lab.
"If we were to stop emissions entirely of all greenhouse gases right this minute," he reckons, "we'd see roughly another half a degree centigrade ... by the end of the 21st Century."
That’s almost a full degree (Fahrenheit) already in the pipeline. So even if we shut down all emissions — which is not happening — we might still get to the 3.5 F threshold where scientists say the worst effects of climate change would kick in. (This is normally expressed by scientists as 2 degrees Celsius, which is the same as 3.5 F).
But Wait, There's More!
"We're seeing years now that basically blow the roof off of records that have been maintained by the National Climate Data Service back to the late 19th century," notes Collins — and then a remarkable thought occurs to him:
"None of the students in my classes have grown up in a normal climate," he adds. "None of them."
Think about that. On the flipside, if you’re over, say 30 years old and can actually recall “normal," well, that’s over.
"I have to say that all the projections that were made 30 years ago are still valid," says Fung. "The only thing we had not anticipated ... is that the CO2 increases much faster than we ever thought that it would."
Despite the pledges made in Paris by nearly every nation in the world (the U.S. is alone among signatories in backing out of the climate accord, under the Trump administration), emissions are still rising. And even those historic commitments — if they’re all kept — won’t be sufficient to turn things around.
"No, we're already beyond that," says Fung. "The commitments, I think, are very good start, but they're just not adequate."
Don't Give Up the Ship
All this grim talk might lead one to ask what point there is in trying to reverse the climate train. But recently refined climate models suggest that aggressively cutting emissions could improve future life on Earth in significant ways — or at least blunt the impact of continued warming. It could, for example, reduce periods of extreme heat in Sacramento from two weeks a year to as little as two days. The Sierra snowpack might shrink by “just” 20 percent, rather than 75 percent. That’s the optimistic scenario.
This week's climate summit will pull together mayors, state and provincial governors, scientists and corporate leaders to keep momentum going with "subnational" actions to reduce greenhouse gas emissions. They'll be joined by major players such as former Vice President Al Gore and former Secretary of State John Kerry, who signed the Paris accord on behalf of the U.S. with his tiny granddaughter perched on his lap.
One of the themes attendees will discuss is, "key building blocks required to peak global emissions by 2020," a goal that seems wildly optimistic given current trajectories and with most of 2018 already behind us.
"First thing we have to do as a global community is reverse course rather sharply," says Collins. "We think it is technically feasible."
Technically feasible, perhaps — but not easy. California, for instance, has the nation’s most aggressive efforts to cut greenhouse gases and overall, it’s working: total emissions are down 13 percent since 2004. And still, climate emissions from cars and trucks have been on the rise in recent years.
"Our cars are literally our time machines," says Collins.
But unlike Doc Brown's Delorean in the 1983 film, Back to the Future, Collins says most cars are driving us backwards.
"They're taking the atmosphere to a chemical state that it has not been in for millions of years." he says. "Currently, we have as much carbon dioxide in the earth's atmosphere as we did five million years ago."
The world 5 millions years ago was not “our” world. There were early ancestors of humans and the first tree sloths, but mammoths had yet to appear.
"Our steam engines, our factories, our cars, in the space of a little over 230 years since the start of industrialization, since the first steam engine," notes Collins. "In 230 years they've taken us back five million years."
And Collins says we have about 25 years — roughly one generation — to reverse course.
He and Fung both have their glimmers of optimism that technology and the boom in solar, wind and other forms of clean energy could quickly reduce climate emissions. Fung points to the young college students passing by us on campus as her best hope.
"I think I am optimistic about the young people. I'm optimistic that they are taking — they’re very proactive about the future."
But Fung and Collins agree that time is what’s running out.