When Governor Arnold Schwarzenegger signed California's landmark climate strategy into law in 2006, he laid out the mission succinctly.
"We simply must do everything we can that is in our power to slow down global warming before it is too late," he declared at the September 27 signing ceremony.
Ten years later, few would argue that California hasn't done its fair share in the fight against climate change. But the question of how much the Global Warming Solutions Act, still known by its legislative shorthand as AB 32, has actually cut California's greenhouse gas emissions, is tougher to get at.
"I think that it worked," says Jeffrey Greenblatt, a staff scientist at Lawrence Berkeley National Laboratory.
But to paraphrase a former president, it depends on what your definition of "it" is. So, he amplified.
"I think that AB 32 plus the suite of complementary policies that have come in its wake have been an overwhelming success."
If anyone knows, it would be Greenblatt. He's one of the few people who have actually run the numbers. It's tricky because AB 32 only embodies a portion of California's sweeping assault on climate change. It authorized the state's carbon emissions market, known as cap and trade, and set in stone the goal of cutting climate emissions back to 1990 levels by 2020.
But the actual plan to get there has been a patchwork of policies aimed at everything from reducing auto tailpipe emissions (the state's largest single source of greenhouse gases) to ratcheting up the proportion of electricity generated from "clean" sources like solar, wind, and geothermal energy. Even a law (with no actual teeth) to contain urban sprawl and reduce the miles that people drive in cars has possibly made a dent.
"All these things are starting to come in," notes Greenblatt. "And while I would argue that they're not strictly a direct result of AB 32, they are heavily influenced by its existence."
As of 2014, total emissions were down nearly 10 percent from their peak in 2004, but for a complex web of reasons.
Undoubtedly, the steep drop in emissions during the three years or so starting in 2008 was largely driven by a jarring economic recession, which stifled economic activity in general, pulling emissions down with it.
"We kind of got some headway for free, as it were," says Greenblatt.
Still, he calculates that if California "turned off" that constellation of measures back in 2010, more than 100 million metric tons of additional greenhouse gases would have been pumped into the atmosphere. That's equivalent to almost three months of California's total emissions in 2014, the last year for which regulators have data.
Greenblatt says that cap and trade, often described as the centerpiece of California's climate strategy, "doesn't really account for a whole lot of emissions reductions." The carbon trading program, which has been in full swing for only about two years, sets a declining cap on industrial warming gases while allowing businesses to buy and sell pollution permits with one another.
"But what's really started to happen," Greenblatt adds, "is a lot of complementary policies have passed or gone into effect that have sort of naturally reinforced AB 32."
The authority of AB 32 to reach beyond 2020 is also a matter of debate, though that debate was at least partially squelched by a new law (SB 32) that sets the bar substantially higher: to slash emissions 40 percent below 1990 levels by 2030. That will be a much bigger lift.
The California Air Resources Board has drafted a "concept paper" with different scenarios that could get the state to its 2030 goal, and has determined that existing measures won't be enough to do the job, if that weren't already obvious.
"Taking another 40 percent of emissions out of a growing economy in ten year's time is going to be very ambitious," says Greenblatt, with his gift for understatement. But he says the mere presence of AB 32 has helped maintain momentum in California's quest to quash climate emissions.
"That is making policy planners, lawmakers and others at the state level think long-term about, 'What else do we need to do to keep CA on track to hit this very ambitious long-term target?'"