It figured to be a lovefest when Jerry Brown stepped up to the microphone at the California Democratic Party’s convention in March. He was kicking off his campaign for a fourth term as governor of the state that ranks as the world’s eighth-largest economy and perhaps its leading environmental trendsetter—a reputation Brown himself helped create during his first two terms as governor, from 1975 to 1983, when he rejected nuclear power, championed wind and solar, and shrank California’s electricity demand without slowing the economy.

Brown began his twelve-minute speech by touting the economic achievements that make him the heavy favorite to win re-election in November. “California is back!” he shouted, citing the 1 million new jobs that have been added since the recession and the budget surplus that allowed the state to establish a rainy-day fund.

But the celebratory mood didn’t last. Discussing the historic drought now gripping California, Brown pledged to manage the state’s water “in a careful, efficient and wise way.”

Which is when the hecklers struck. Shouts of “No fracking!” and “Ban fracking!” rang through the hall.

“I got it,” said Brown, raising his hands to quiet the outburst. Pressing ahead, he said: “A key challenge facing California is not just drought today. It’s climate change, now and forever.”

Strong words, but they triggered more shouts of “No fracking!” Brown looked annoyed. His own voice rising, he shot back: “I challenge anybody to find any other state” that’s doing as much against climate change as California is. The governor cited his goals of reducing the state’s CO2 emissions by 25 billion tons by 2020, while obtaining at least 33 percent of its electricity from renewable sources. California, he added, has 30 percent of the country’s electric cars, and it encourages energy-efficient buildings and appliances. But the shouts of “No fracking!” continued.

Would that it were so simple, responded Brown, adding that no “one thing” is enough to fix climate change. The governor concluded by urging “every one of you in this room to join in a crusade to protect our climate…. And keep protesting,” but add a lot more stuff.

“We wanted to send the governor a message that climate leaders don’t frack,” said RL Miller, who as chair of the California Democratic Party’s environmental caucus helped organize the protest. “Fracking in California is aimed at oil, not at natural gas like in other parts of the US,” Miller told The Nation, “and the climate impact of fracking the Monterey Shale”—a deposit that covers much of the Central Valley and has been projected to contain nearly half as much oil as Saudi Arabia—“would be as bad or worse than building the Keystone XL pipeline. If we can’t stop fracking in California, with our environmental ethos and a governor who’s doing good things on climate change, where can we stop it?”

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“There are still a lot of people who don’t know what fracking is,” said Dan Jacobson, the legislative director of the nonprofit Environment California. “Half of them think ‘fracking’ is either a bad word or part of the vocabulary on Battlestar Galactica,” a TV show whose sci-fi characters use “frack” as a substitute for the F-word.

Jacobson and other environmentalists argue that the climate crisis does not allow any expansion of fracking, and they recently received inadvertent support from none other than President Obama. In an interview for the Showtime series Years of Living Dangerously, Obama stressed that avoiding the worst damages of climate change requires limiting the global temperature rise to 2 degrees Celsius. Saying “science is science,” Obama added that he accepted the latest scientific finding that respecting the 2°C target means that no more than one-third of the earth’s known fossil-fuel reserves can be consumed prior to 2050. “We’re not going to be able to burn it all,” Obama said. “Over the course of the next several decades, we’re going to have to build a ramp from how we currently use energy to where we need to use energy…so that you have a tapering off of fossil fuels replaced by clean energy sources that are not releasing carbon.”

This new scientific imperative—to leave two-thirds of known fossil fuels in the ground—has not yet penetrated most policy discussions, much less media coverage and public awareness, but its implications are staggering. Among other things, it all but rules out fracking. After all, if humanity can burn only one-third of the earth’s remaining fossil fuels, which are largely accessible already, what role is there for a technology whose sole purpose is to extract exceptionally hard-to-reach deposits of oil and gas?

Unlike conventional oil drilling, fracking injects vast amounts of water, sand and industrial chemicals such as benzene into the earth at extremely high pressure, shattering rock and freeing the oil or gas below to be pumped to the surface. In effect, fracking creates new reserves of product that energy companies can bring to market—which is what makes it incompatible with the 2°C target. “Fracking is all about accessing the remaining two-thirds of earth’s fossil fuels,” said Jacobson. “Instead of finding new ways to get fossil fuel out of the ground, we need to focus on rapidly developing clean energy sources.”

How does Jerry Brown square his call for a “crusade to protect our climate” with allowing fracking in California? The closest the governor has come to answering that question publicly was in a radio interview conducted shortly after the heckling incident at the Democratic convention. Brown was asked, “Can you really have a meaningful climate-change pact if you don’t address fracking?” He replied, “The premise of that assertion is that climate change is primarily about fracking. And that’s the most absurd idea I’ve ever heard.”

Governor Brown and his top aides declined to be interviewed for this story. Instead, press secretary Evan Westrup made available Jason Marshall, the deputy director of the Department of Conservation, which oversees the Division of Oil, Gas and Geothermal Resources, or DOGGR—the state agency that regulates oil and gas drilling in California. Marshall told me he was unaware of the studies showing that two-thirds of known fossil-fuel deposits must be left in the ground, adding: “The governor has been very clear” about moving to renewable energy sources, but “we need to make sure we’ve got energy security and available resources here now, even as we’re moving forward.”

California consumes about 15 billion gallons of oil a year, 37 percent of which is produced within the state. Fracking, however, would not necessarily change that percentage. Oil is sold on the global market, so there is no guarantee that oil fracked in California would actually be consumed in California. Nevertheless, the state needs oil, and it has to come from somewhere.

In May 2013, Brown called fracking “a fabulous economic opportunity” that he had to balance against his commitment to climate protection. He has resisted calls to sign an executive order imposing a moratorium or ban on fracking, which as governor he has the authority to do at any time. Instead, last September he signed California Senate Bill 4, which allows fracking to continue but requires drillers to notify regulators and nearby residents in advance; SB 4 also requires the state to monitor water quality near fracking sites, and to complete a study of fracking’s environmental and other implications by 2015. (In 2005, George W. Bush signed a law that largely exempts fracking from the Clean Water Act, the Clean Air Act and other major federal oversight.) In case anyone still wondered, Mark Nechodom, the director of the Conservation Department, told a public panel last October in no uncertain terms: “Governor Brown supports hydraulic fracturing.”

Environmentalists have also voiced suspicions about the $500,000 that Occidental Petroleum, long one of California’s top oil companies, contributed to Brown’s campaign in 2012 to pass Proposition 30, which raised taxes on wealthy Californians to fund increased spending on public education—generally not the kind of initiative that big corporations favor. Occidental’s contributions came a few months after Brown fired the previous director and deputy director of the Conservation Department, following complaints from the oil industry that DOGGR was too slow in granting drilling permits. When a Los Angeles Times article linked the two firings to industry complaints, the governor’s office pointedly did not issue a denial.

“That was a clear signal to the industry—both the firings and the nondenial,” said a former administration official familiar with the decision.

“I can’t really comment on the reason [the previous regulators] were asked to leave,” said Marshall. “I wasn’t here.”

So in the fall of 2013, activists started getting in Jerry Brown’s face on fracking. Protesters began appearing outside events where he was speaking—for example, at the governor’s mansion in Sacramento in November, where they shouted “Climate leaders don’t frack!” loudly enough that aides had to move Brown’s podium farther from the street.

“Governor Brown is in a tough position,” said Bill Allayaud, the California director of government affairs for the nonprofit Environmental Working Group. “He is a climate leader…. And yet he’s had a hard time saying no to the oil companies the last couple of years.”

Whether because of the pushback or not, Brown’s position on fracking seems to have evolved. “These are hard questions,” he said in May about fracking’s environmental and economic implications. DOGGR is “reviewing this,” he added, and Brown wants all sides to “participate and offer their best thoughts.”

But by far the biggest development in the fracking debate is one Brown had nothing to do with: on May 20, the bottom dropped out of the economic case for fracking in California when federal officials slashed—by a whopping 96 percent—their estimate of how much recoverable oil is contained in the Monterey Shale. So much for the initially projected 13.7 billion barrels of oil that had oil companies salivating. The Energy Information Agency’s new estimate is that the Monterey Shale contains a mere 600 million barrels of oil. “This [EIA] report hammers the final nail in the coffin for oil companies’ ludicrous claims that fracking is the key to California’s prosperity,” said Zack Malitz, a campaigner with CREDO, an activist group coordinating opposition to fracking in the state.

This is by no means the end of the story, however. The Western States Petroleum Association, an oil industry trade group, argued that the EIA was talking about “technically recoverable” oil—that is, oil that can be extracted under current technological conditions. There is still plenty of oil down in the Monterey Shale, the WSPA pointed out, and “we have a great deal of confidence that the skill, experience and innovative spirit possessed by the men and women of the petroleum industry will ultimately solve this puzzle and improve production rates from the Monterey Shale.” In other words, we haven’t figured out how to get that oil out yet. But we will.

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California’s Route 33 is known locally as the Petroleum Highway. And for good reason: up and down this road about 100 miles northwest of Los Angeles, hundreds and hundreds of oil wells dot the dry desert landscape. The highway passes Elk Hills, whose oil was key to the Teapot Dome scandal that sullied President Warren Harding in the 1920s. Often stretching as far as the eye can see, the hundreds of wells straddling the Petroleum Highway are each topped by a pump jack, a metal contraption sometimes nicknamed a “nodding donkey” for the way its snout dips up and down, up and down, as it relentlessly sucks oil from some of the largest deposits on earth. These deposits help explain why California, despite its environmental reputation, is the third-biggest oil-producing state in the country, behind Texas and North Dakota—no small achievement, now that Obama’s “all of the above” energy strategy has lifted the United States past Saudi Arabia as the biggest oil producer on earth.

Welcome to Kern County, epicenter of California’s oil production since the first big strikes in the 1890s and the place where most of the state’s fracking now occurs. The fracking to date has been relatively straightforward. Vertically driving existing well shafts deeper into the earth has enabled oil companies to exploit previously inaccessible resources. Marshall told me that of the roughly 4,500 drilling applications DOGGR receives every year, about 1,500 involve fracking or other forms of enhanced well stimulation (including methods whereby acid or steam is pumped underground to force oil or gas to the surface).

But the fractured geology of the Monterey Shale makes fracking more complicated, Marshall said: “The new fracking is horizontal, and it’s really quite a different technology.” The driller is “turning a well on its side,” he added, and threading it through the dips and folds of the shale. Jacobson of Environment California offers a nongeologist’s analogy: “The shale in North Dakota looks more like lasagna—it’s very layered. In California, it looks more like a very large plate of nachos.” Penetrating such complex geology is a challenge that oil companies have not yet mastered, though Marshall expects they will: “We haven’t seen a big rush of notices of intent to drill into the Monterey…. But when they figure [it out], I think we’ll start to see the notices.”

Kern County, however, is also a world-class agricultural power. It sits at the southern end of California’s Central Valley, which produces nearly half of the country’s fruits, nuts and vegetables each year. This is possible only because the desert is irrigated by vast quantities of water. Since the process of horizontal fracking a single oil well requires millions of gallons of water, fracking worries some farmers—especially given that the current drought, one of the worst in California’s history, shows no signs of relenting.

Tom Frantz grows almonds in central Kern County, living in the same house where he has spent most of his sixty-five years. Historically, Kern’s oil operations were concentrated in the west of the county, along the Petroleum Highway. But in the last ten years, Frantz said, fracking has spread to the valley floor, where farming traditionally dominated. His farm is now surrounded on all four sides by fracking operations, Frantz told me, “and every one of them needs water.”

Even more troubling than fracking’s need for fresh water is its potential to contaminate the water it uses, Frantz added, whether because a well casing fails or because an oil company doesn’t obey the law. In 2012, Frantz videotaped an Occidental subsidiary illegally dumping black liquid into a nearby waterway; after the video appeared on television, the state fined the company $60,000.

One recent spring morning, Frantz strode into his orchards and bit open an immature almond. “Right now, this almond is 100 percent water,” he said, pointing at its jelly-like center. “Everything in this almond is dependent on what’s in the soil and what’s in the water…. The first time something shows up in our almonds, a little benzene, no one’s going to buy almonds from here anymore. We grow 2 billion pounds of almonds a year; it’s like a $5 billion industry. Fracking has the potential to wipe that out.”

Students and teachers at the Sequoia Elementary School in the nearby town of Shafter are also nearly surrounded by fracked wells. As kids chased one another across the playground, two nodding donkeys bobbed up and down barely a football field’s distance away; a third, elevator-style well was pumping nearby. On the other side of the playground was an organic garden, established by the nonprofit Center on Race, Poverty and the Environment. “Last year, when we had the grand opening of the garden, we noticed they were putting those pumps up; some drilling was going on,” said Juan Flores, an organizer with the center. “The smells could be so bad that it could actually hurt you. You could get headaches, be dizzy, get nauseous.”

Nick Ortiz of the Western States Petroleum Association told me that SB 4 provides Californians with the strongest regulatory protection in the country—though he later conceded that his industry had not backed the bill—and insisted that “there has not been a single confirmed case of fracking causing health problems.” But complaints similar to those in Shafter have come from people living near fracking operations in other parts of the country. In May, a jury in Texas awarded a family $2.9 million in damages after they sued Aruba Petroleum for poisoning their water and livestock. The Southwest Pennsylvania Environmental Health Project has documented twenty-seven cases of residents near fracking sites suffering from breathing problems, skin rashes, nose bleeds and headaches.

Rosario Garcia, a 43-year-old father of four who works a plot at the community garden, said he has suffered for two years from valley fever, or coccidioidomycosis—a disease that gave him a high fever and difficulty breathing. “You feel like you need to cough, but you can’t,” he said in Spanish. Valley fever is common throughout the Central Valley; it’s caused by fungi in the soil getting stirred up by things like farming and oil drilling. Garcia says two of his best friends died from it. Now, his 9-year-old son Miguel has been diagnosed with asthma; a younger son is also developing breathing problems.

“When I have asthma, my chest hurts; I have headaches,” Miguel said, speaking the English he learned in school. “I feel like if I was going to die. I get mad because I can’t play outside with my friends.”

Fracking may turn out to be Jerry Brown’s Keystone XL pipeline: a high-profile test of his climate commitment in which scientific fact clashes with political reality. Like Obama, Brown clearly grasps the urgency of the climate crisis and has taken important steps to address it. As former California State Senator Tom Hayden has reported, Brown has amassed what amounts to a green budget that could enable the state to spend as much as $120 billion over the next five years to help make California 100 percent carbon-free by midcentury.

But it is the historical fate of both Brown and Obama to be in power at a time when good intentions and steps in the right direction are no longer sufficient. The science they face makes demands that seem preposterous within the political and economic status quo. On a planet where two-thirds of the fossil fuel must stay in the ground, it’s not just fracking and Keystone XL that can’t go forward. The scores of billions of dollars that companies invest in oil and gas exploration also make no sense: Why explore for fuel that can’t be burned?

Doing all that’s required to avoid climate catastrophe—including saying no to Big Oil—amounts to an overturning of the existing order, even a revolution. Perhaps it’s unfair to expect Brown or Obama to lead such a revolution; government officials rarely do. But science does not care about fair, and leaders inherit the history they inherit. What matters is what they, and the rest of us, make of it.