To drive into Houston from the east is to glimpse the beating heart of a petrochemical empire: south from I-10, fifty miles of facilities ring the Houston Ship Channel and the Galveston Bay below. Up close, the complex gives the photonegative feeling of beholding the ocean, or a mountain range. Drums holding millions of chemical gallons sigh eternally into the balmy air. Skeletal smokestacks belch streams of fire like the Olympic torch. You might expect to find the Terminator retired there.

Hurricane Harvey hit Houston hard, but the city was lucky in one regard. Climate scientists and hydrologists have long feared that a poorly placed storm could send a surge up the Galveston Bay and into the Channel, where the narrowing waterways would magnify the surge's height and send it tumbling over barriers into the refineries. And that, environmental attorney Jim Blackburn predicts, "would be the worst environmental disaster in United States history."

Harvey offered a miniature preview of what might happen, when an Arkema chemical processing plant flooded in Crosby, northwest of Houston, and a tank of organic peroxides exploded, sending a black plume skyward. First responders arrived unprepared, and, according a lawsuit filed after the storm, "one by one, the police officers and first responders began to fall ill in the middle of the road," vomiting and choking. The dreaded storm surge would magnify that risk a thousand-fold—petrochemical drums would be lifted off the ground by the water, allowing their contents to slip into floodwaters and poison those unlucky enough to live nearby. Houston would be under double threat. "People are going to die because of the floodwater," Blackburn says, as they did in Harvey, "not to mention the oil and hazardous substances." As the waters receded, they would destroy one of the most prolific estuaries in the country—both in commercial and biodiverse terms—and choke out the wildlife in the bay itself.

Yet, curiously, the companies lining the Channel have shown little urgency in protecting their plants. The plan to build an "Ike Dike" has been discussed since Hurricane Ike hit in 2008, and while that talk has again heated up in Harvey's wake, there has been little movement as yet. Greater Houston processes two of every five barrels of petroleum in the U.S., and half of American jet fuel. Major damage to the facilities in the channel would cast a pall on the national economy.

In Houston, some folks are starting to think about what might happen when the oil and gas industry fades. While the city's economy has diversified in recent years, economists still attribute around 45 percent of its economic activity to the industry—down from nearly double that number in 1980.

The risk of a storm surge makes the threat to the industry literal, but market pressures and the possibility of stricter climate legislation—still remote in Texas, but increasingly common worldwide—are already nipping at the industry's heels. In the heart of the Shipping Channel petro-complex, environmental justice advocate Yvette Arellano points out a telling sign: gigantic bundles of blades and columns for wind turbines, waiting to be shipped north. Renewables lounging in the belly of the beast. "It lets you know that change is happening," Arellano says. "Whether they like it or not, it's happening. And oil and gas isn't going to stand behind. They're going to move forward too. They don't want to lose money."

In Houston, some folks are starting to think about what might happen when the oil and gas industry fades.

Texas already is the nation's largest producer of wind energy, at three times more than second-place Iowa in absolute terms. North Texas houses the nation's second and third largest online wind farms. As the New York Times reported last year, renewable fuel sources are quietly becoming more economically viable, with red states putting the technologies most heavily to use. In 2010, NRG, an energy giant headquartered in Houston, bought Green Mountain Energy, at the time the nation's largest provider of renewable energy, wagering that more customers were shading green.

Blackburn has been an environmental advocate in Texas for decades, and now, post-Harvey, he is having his moment. With a principled white mustache and a steady gaze, his resemblance to the Lorax is more than philosophical. Still, he is not blind to economic realities. He sees the market forces and cultural undercurrents and worries about the future of the oil and gas industry. "It's just a question of if they're going to adapt or not," Blackburn says. "And it's in our best interest as a community for them to adapt and start adapting soon, because otherwise all these jobs are going to disappear, we're going to be like the Rust Belt."

Environmental justice advocate Yvette Arellano and her exhaustive catalogue of petrochemical spills.

The transition to renewable energy, so far as it goes, will take time, and in the interim there is much to be done. Rice University soil scientist Carrie Masiello breaks down the climate change puzzle into a few broad categories. Outside the classroom, she is still teaching, charting invisible diagrams across her desk with her hands as she considers the science. Renewables help to prevent the release of new CO2—a prime contributor to global warming—into the atmosphere. Another piece of the puzzle, though, is how to get the CO2 already in the atmosphere out.

The latter process is referred to as carbon sequestration—taking atmospheric carbon dioxide and storing it inertly in the ground. This can either be done in deep carbon wells through industrial processes, themselves energy-intensive, or through surface sequestration, which occurs within a few feet of the atmosphere.

The Houston area has already begun sequestering carbon. NRG has put an experimental scrubber into its coal-fired Petra Nova plant. The scrubber captures 10% of the plant's carbon dioxide and pumps it 90 miles away into flagging oil wells, boosting their productivity. The economic viability of the technology depends on the price of the additional oil produced, but finding a way to make such technologies affordable could mean their dissemination to coal plants worldwide. Still, the project carries a whiff of farce, as it uses captured carbon to pump extra carbon-emitting fossil fuels that might otherwise remain in the ground.

But Houston also has an enormous surface-level carbon sink: its prairies. The last piece in this series examined how prairies could aid in the battle to stop flooding, by enhancing the land's absorption of rainwater. The same deep roots that allow the prairies to sponge water up also allow the tall grasses to absorb atmospheric carbon.

Grasses, unlike trees, put half of their biomass underground in extensive root systems. Masiello explains that this half-hidden pattern evolved as part of a "long-term evolutionary arms race between grasses and grazers," to protect the plants when grazers eat their heads. The deep root structures allow the grasses to "pump carbon down" into the ground, where it is stored both in the roots themselves and in the soil.

Blackburn hopes to put prairie grasses to use in offsetting emissions. He has outlined plans for a Texas Coastal Exchange: farmers and ranchers outside of Houston and along the Texan coastline will track the carbon levels in their soil and, seeing an increase, sell the sequestered carbon to companies who hope to "offset" their emissions, by buying a grounded amount equivalent to the carbon that their business produces. "Once you've done avoidance and minimization" of carbon emissions, Blackburn explains, "the only thing left is removal. And the only feasible technology out there is nature. It's a wonderful irony that nature may actually be the solution for the future of the oil and gas industry."

The TCE functions roughly like a cap-and-trade program, minus the legal cap on how much carbon businesses can emit. "Basically, we're trying to package that, and turn it into a commodity, so that it can be bought and sold and traded," Blackburn says. "So farmers and ranchers can make money off of restoring native prairies, off of certain types of grazing techniques that can increase the carbon content of their soil, that can supercharge carbon into the subsurface."

The last piece in this series examined how prairies could aid in the battle to stop flooding, by enhancing the land's absorption of rainwater. The same deep roots that allow the prairies to sponge water up also allow the tall grasses to absorb atmospheric carbon.

Unlike other carbon-offset programs, which often balance emissions by investing in more efficient technology, the TCE aims to directly remove carbon from the air. Its scope is local, and the prairies, proponents point out, are broadly useful besides. Ranchers and landowners with dwindling yields outside of Houston could make their land economically viable without selling to developers, by selling off the carbon rights and grazing cattle on their lands—not to mention the potential for ecotourism and hunting. The grasses, especially west of Houston and along the coast, would help ameliorate flooding and preclude subdivisions in flood-prone land.

Blackburn trusts that buyer preference for carbon-neutral goods will spur corporations to act. "Frankly, consumers voting with their money make an incredibly powerful tool," he says. "And we've never used this to achieve social goals to the extent we now have the capability to."

That purchasing power goes both for the ultimate consumers of goods being produced, and for investors. Blackburn points to the University of California pension fund's 2015 divestment from oil sands (along with coal), "because they're concerned that it's not a good financial investment." Currently, the Massachusetts and New York district attorneys are suing ExxonMobil for misleading investors into undue optimism by suppressing unfavorable climate science. Strong governmental action on climate change might mean that oil companies' assets get stranded, if they are forced to leave fossil fuels in the ground. With that in mind, ExxonMobil decided in December to disclose its analyses of the risks that climate action poses to its business, after shareholders voted for greater transparency.

Bull under a big sky in the prairie west of Houston.

Despite Blackburn's characterization of the Exchange as a "win-win-win," questions loom. The most obvious is whether companies will buy into the exchange, especially oil and gas companies themselves. On that count, Blackburn is optimistic. Responding to a hypothetical in which, say, Shell pledges to go carbon neutral, and suddenly their gas is fifteen more cents per gallon, he asks, "Would you be willing to pay ten cents or twenty cents more per gallon, and not contribute to global climate change? Many would not, but some would. And, in listening to the oil companies, if they could offer a product that would lure ten percent of the market off their competitors, hell, that may be enough to tip the balance for them. These companies have a tremendous amount of money at stake for five percent or ten percent of the market."

The success of the Exchange will depend on enough consumers willing to pay an environmental premium across goods. That demographic may or may not exist. Even if it does, prairies will soak up a chunk of atmospheric carbon while fossil-fuel burners soldier on. That bothers environmental justice activists like Arellano, who believe that cap-and-trade programs allow for an ease of conscience for consumers and corporations while failing to address more urgent problems that polluted communities near refineries face. "In an area that's already devastating poor, low-income people of color, you're saying it's okay to alleviate the emissions, because this is one world, and as one world we're making a decision to cut those carbon costs," Arellano says. "But the people who are going to suffer at the hands of cutting the carbon costs for all those other folks are the same ones that have had to bear the burden of disproportionate environmental impacts."

The TCE prairie plots, Arellano points out, would be to the west of Houston, to the north, and to the south along the coast—everywhere, seemingly, but east Houston, where so much of the heavy industry is concentrated. She agrees with Blackburn on the need for the Ike Dike, an important line of defense for East Houstonians especially, but finds the TCE lacking. "We need change. We've been needing change forever," she says. "And that change isn't just a cap-and-trade program, that change isn't just placing solar panels on homes. We need a just transition where you have community members sitting at the table, making those decisions along with policy-makers. We need representation, because at it stands in the Deep South home of oil and gas, you're going to have racism that's going to permeate policies."

"The people who are going to suffer at the hands of cutting the carbon costs for all those other folks are the same ones that have had to bear the burden of disproportionate environmental impacts."

A more just transition takes introspection, a city with some self-awareness. And in Houston and Harris County political circles, like in Texas writ large, talk of climate change is largely taboo. Jaime Gonzalez, community conservation director of the Katy Prairie Conservancy, works to protect the prairie lands west of the city. He believes that the prairie can help spur more honest introspection. The city, he says, is like an "aging teenager trying to get into adulthood—they didn't like what their parents did, they're always looking towards the future, and they're running 12,000 miles an hour."

"The great thing is there is a lot of energy there, there is a lot of innovation, there is a lot of 'let's try new things,'" Gonzalez says. "But also, it makes the city seem shallow at times. Because people come here, and they live in subdivisions that look the same, they go to the same big box stores, and everything becomes kind of Legoland."

Houston's forward-facing approach means that present-day concerns are neglected in favor of growth. Blackburn sees this as a "fundamental issue."

"I think we have spent more time in Houston trying to accommodate homes for those who are yet to come, for those we want to attract here, rather than protecting the people we already have here," he says. Arellano, the environmental justice advocate with a yet more immediate mandate, would surely agree.

Gonzalez hopes that as Houston approaches its bicentennial, twenty years from now, it will slow a bit and take stock, celebrating "the things that make the place easier to understand and to hold on to." The city's biological heritage is one such thing, its heirlooms felt throughout the culture. "The city's more understandable when you find that the reason we have so much barbeque here is because we used to have so much cattle ranching. The reason that we have the rodeo is because this is a very cow-heavy place. The reason that we have country music evolving here is because it was resonating with the people that were here. If you look at all the sports teams in Texas, except for the Astros and the Rockets…just about every single major sports team is a reference to the prairie."

Houstonians are a people of the prairie, but in the megalopolis it can be easy to forget. With so many newcomers—greater Houston added 159,000 residents in 2016 alone—it can be hard to feel tied to the flora-filled past. "We conceive of the work that we do as reintegration," Gonzalez explains. "Trying to reintegrate nature into community, trying to reintegrate literally the fabric of living things with the built environment"—rootedness through roots.

The Texas Coastal Exchange integrates the local carbon cycle by linking emissions with the idea that, in a balanced system, they need some place to go. While the Exchange could reduce atmospheric carbon levels, even Blackburn's most optimistic estimates bite out only a tiny chunk of the earth's excess, a number increasing by the year.

That shortfall leaves him undeterred. "We're gon' take it a step at a time," he says. "We figure that Texas has the largest carbon footprint of any state in the United States. We can get to work on that. Harris County has the largest footprint of any U.S. county. We can go to work on those smaller scales. There's plenty of carbon."

The greatest utility of the Texas Coastal Exchange may be that it helps Houston "get to work." Right now, even as oil and gas companies make their advertising greener, the federal and Texas governments are undercutting climate research and slashing regulations. Texan legislators can sneak climate change into public discussion by talking about "weird weather," but the attention paid is oblique at best. But if corporate interests in Houston were able to address climate change in a way that allowed them to take action, the conversation could become more robust.

"The Texas Coastal Exchange is one of those projects that interjects a strong ray of optimism into this whole situation," Blackburn says. "With both climate change and the future of the Texas coast, and potentially the future of the United States relative to the climate." Soil carbon monitoring, the first step in establishing the Coastal Exchange, will begin sometime this year.

Sammy Feldblum studies geography at UCLA and reports across the southern half of the United States.