This liberal-minded city likes to think of itself as unique in Texas, a blueberry in the tomato soup of red-state politics. The state capital, it is home to the University of Texas, and, on the outskirts, to the Center for Maximum Potential Building Systems, an obscure and quirkily-named nonprofit responsible for putting Austin on the map as a maverick of the green movement.

Max's Pot, as the center is nicknamed, was instrumental in Austin’s experimental program to curb the energy appetite of its buildings.

Pliny Fisk III, the center's founder, devised a rating system to measure how materials used in construction affect energy use. His brainstorm became the basis of Austin’s green building program, the nation’s first—and Austin went on to international acclaim after the program won an award at the United Nation’s Earth Summit in Rio in 1992.

Now, 24 years out from Rio, Austin is again at the forefront as cities around the globe are reinventing themselves in order to sustain urban life in the face of population growth and climate change. Austin is part of an expanding roster of cities pledging to become “carbon neutral” by 2050—and, to get there, Austin has, without a big public drama of resistance, adopted a tough new standard that all new homes are to be rated net-zero capable, meaning they produce as much electricity as they consume.

View Images A lifeguard patrols Barton Springs Pool, Austin’s most beloved public space, home to the endangered Barton Springs salamander. Saved from polluting runoff in the 1990s, the iconic pool is fed by natural springs that keep its waters at 68 degrees and is open year-round. Photograph by Benjamin Rasmussen, National Geographic

“Cities can do what countries can’t,” Fisk says, arguing that the greatest gains in the fight against climate change will be made at the local level. As conservatives in Congress who reject climate change science thwart efforts to reduce greenhouse gases and other measures, American cities are pressing ahead to shrink their carbon footprint. Nearly 2,400 city-led climate change initiatives are quietly underway from Portland to Philadelphia.

These cities are reengineering streets, wiring, and sewers to limit vulnerability to drought, flash floods, and other perils of a warming earth that already bedevil nearly every large urban area worldwide. Cities are also incubators of new technology and strategies for reducing greenhouse gas emissions, including green building programs. (Read about the role of Austin’s zero-waste initiative.)

That's because buildings are among the planet’s biggest energy guzzlers. Conventional buildings consume two-thirds of the world’s energy and produce more than a third of its carbon emissions. (That figure jumps to 40 percent in the United States.) Green buildings, on the other hand, use, on average, 30 percent less energy.

Austin’s 5-star rating system is said to have been a model for LEED (Leadership in Energy and Environmental Design), today’s international standard for certifying green buildings, based on elements such as water use, energy efficiency, materials, and indoor environmental quality.

View Images An early disruptor, Pliny Fisk III helped found Austin’s green building program, which became a model for others. While on the faculty of the University of Texas architecture school, Fisk created a nonprofit center for sustainable design and experimentation. This Airstream was once a centerpiece of a solar-based student design competition. Photograph by Moland FENGKOV, HAYTHAM-REA, Redux

Growing Pains

Austin's green building movement dates to the 1970s, when residents fought a nuclear power plant that the city planners decreed was necessary to meet the city’s increasing power needs.

“They told us we needed this incredible amount of power,” says Peter Pfeiffer, an Austin architect who designed houses to deflect heat from the blazing Texas sun. “Then somebody had the creativity to ask: based on what assumptions? Why don’t we manage demand a little more aggressively? And that was the birth of Austin’s green movement.”

A larger environmental movement gained momentum in the early 1990s when a more intensive battle played out after runoff from a new housing development fouled Barton Springs, forcing multiple closures of the city’s beloved public outdoor swimming hole. The 68-degree, spring-fed pool, longer than two football fields, is a treasure, and has long been open year-round. The closures launched the Save Our Springs movement, which, over the next decade, led to tightening of development regulations, including, most famously, enactment in 2006 of the “McMansion ordinance” that limited the size of houses. Even for Austin, its passage was a stunner. It’s still Texas, after all, a state that prizes individual property rights.

View Images A cyclist using an Austin B-cycle, a bike-sharing nonprofit, pauses on the Lamar Street Pedestrian Bridge, which runs over Lady Bird Lake. Photograph by Benjamin Rasmussen, National Geographic

Today the threat to Austin is not the size of the homes but the number of them. Austin is the nation’s fastest-growing metro area, part of a worldwide trend that will turn two-thirds of the world’s population into city dwellers in the next 35 years. Driven by expansion on its outskirts, Austin’s population is on target to double by 2030. (Read about how Austin’s growth impacts its new food future.)

All of that growth feeds sprawl, the natural enemy of sustainable cities. To that end, Austin is filling in its interior, putting up high-rises where parklng lots and decaying low-rise buildings took up valuable space.

“Where you build the building has a much bigger impact than how you design the building. It’s location, location, location,” Lucia Athens, the city’s chief sustainability officer. “Not only is it key to climate change, it’s key to many other sustainability benefits, like living in a compacted and connected community where you can walk to get a quart of milk instead of driving, which is bad for the environment, bad for traffic congestion, and bad for your health."

Austin's real estate prices have also risen with its population, putting housing out of reach for too many. Many have been forced to leave town, adding to Austin's already legendary traffic congestion.

A shortage of affordable housing is approaching a crisis, says Sunshine Mathon, the design and development director for Foundation Communities, a nonprofit provider of affordable housing in Austin.

View Images In the Seaholm EcoDistrict, the courtyard is a venue for music events; residences and businesses like Trader Joe's are built around it. Photograph by Benjamin Rasmussen, National Geographic

Urban Livability

The jewels of Austin’s urban renewal are two entirely new districts that have risen from a pair of defunct industrial sites—a decommissioned, 1950s-era steam power plant and the outdated municipal airport, which closed in 1999.

Both are key to Austin’s efforts to lure 25,000 new residents and workers into the central city. Athens calls the two projects, which are distinctly different, Austin’s “bookends,” framing the kind of urban density the city needs.

“If cities continue to develop in a low-density, sprawling fashion, it becomes impossible to garner enough tax revenue to support and maintain all that infrastructure,” she says.

The Seaholm EcoDistrict is an 85-acre development on the edge of downtown, facing the shoreline of Lady Bird Lake, some of the most sought-after real estate in the city. Once dominated by the city-owned power plant and a water treatment facility, Seaholm today is a high-density, pedestrian-friendly enclave of shops, restaurants, new offices, and open spaces that invite gatherings such as the kind of music events Austin is known for. It is home to a new public library, set to open in May, and several residential high-rises, including one under construction that will be downtown Austin’s tallest building, The Independent, at 58 stories.

On a walking tour, Athens shows off Seaholm’s perks: a small forest of trees, public art works, recharging posts for electric cars, a solar-powered park bench for recharging smart phones and laptops. The Art Deco power plant has been preserved and remodeled into office space, housing a healthcare company and Boiler Nine Bar + Grill, a new restaurant with plans for a roof garden to grow salad greens and other vegetables. Walking paths reconnect the site to the rest of downtown on one side and to a pedestrian bridge over the lake on the other.

Will Wynn, who served as Austin’s mayor from 2003 to 2009, says residents will only buy into such sustainable developments if they can see a benefit.

“You have to show people that the quality of life is measurably better because density is dramatically driving down electricity use per capita, water use per capita, and vehicle miles per capita,” he says. “Growing cities have to find a place where they can dramatically reinvent themselves in a mixed-use, dense way and people clamor for it.”

Wynn, an architect by training, is the only American mayor to have pardoned a pet goat, thus preventing its expulsion from the city for violating an anti-livestock law. At the signing ceremony, the goat ate the paperwork as if on cue, cameras rolling. Less telegenic but more consequential were Wynn's expansion of Austin's green building program and his campaign to develop new power sources from renewable energy. He created what was at the time the nation's largest solar farm on part of a city-owned tract intended to hold a coal-fired plant that was never built.

View Images Energy-efficient design defines this HEB grocery store—part of a Texas chain—in the 700-acre Mueller development, which was once the site of Austin’s airport. The roof is covered in material to reflect heat and also features 11,000 square feet of solar panels, which produce enough electricity to power 16 homes. Both the store and the Mueller neighborhood achieved LEED gold status, an international standard for sustainable buildings. Photograph by Benjamin Rasmussen, National Geographic

Three miles north of downtown, the Mueller development is laid out across 700 acres of the old Robert Mueller Municipal Airport. If Seaholm is urbane and hip, Mueller is more urban village. Like Seaholm, Mueller is a testament to green building. It includes houses and townhouses finished with stonework accents, shops, and 140 acres of open space, dotted with a series of of lakes that double as holding ponds for managing storm water runoff. Twenty-five percent of the residents qualify for affordable housing.

“What makes Mueller Mueller is its 700 acres,” says Mathon. “It is rare to have that kind of acreage sitting around in the core of any city, let alone a boomtown, and the scale of Mueller makes it possible to do things that are hard to do otherwise. “

Project developers are also planting 15,000 trees, including more than 500 native pecan trees saved from a nearby orchard destined for the axe to make way for new development. All that remains of the old airport is a hangar, now used for Saturday markets, and the air traffic control tower, fenced and preserved as a historic footnote.

Mueller’s centerpiece is the Dell Children’s Medical Center, the first hospital in the world to achieve LEED’s platinum (its highest) status. Because hospitals use 2.5 times as much energy as most buildings, Fisk and Gail Vittori, his wife and partner at the center, developed a “green guide” for health care, and Vittori was invited to advise on the planning of the Dell facility. The hospital’s architects incorporated a number of features at odds with conventional hospital design. The entry has a vaulted ceiling, and where a traditional lobby would be painted hospital white, Dell features red Texas stone. Glass walls along one side look down on open-air courtyards landscaped in native plants.

"Why do cancer hospitals get constructed with carcinogenic materials?" asks Vittori. "It happens all the time. With this hospital, we wanted to put health front and center in the context of a green building. This is a pathway for healthy materials to become the standard for hospitals."

View Images Apartments are built across the street from the MLK Jr. station on the commuter rail in East Austin. Once a low-income neighborhood, prices and development have increased rapidly in recent years. A 2014 market study showed a shortage of nearly 50,000 affordable apartments. Photograph by Benjamin Rasmussen, National Geographic

The successes of the green movement are not problem-free either. Pfeiffer, the architect, complains that sustainable programs too often succumb to the allure of technology and overlook the single most important factor in home building: the location of the house in relation to the sun. Laying out a street grid on the wrong axis can mean the difference between house windows absorbing indirect light and direct rays and heat.

That's especially critical in Austin, where a mounting number of hot days have been added to the calendar, along with a larger draw on air conditioning.

New houses tend to be loaded up “like pin cushions,” he says, with solar panels, tank-less water heaters, and other high-maintenance gadgetry that doesn’t necessarily save more energy than low-tech window awnings and weather-stripping.

“It’s like putting a hybrid engine on a 1956 Buick,” he says. “It's still a heavy, clunking car that will only get seven miles to the gallon. How does the sun manifest itself as a problem in our climate? That’s the bigger question to answer.”

The night after the election, while more than 400 University of Texas students staged an anti-Trump rally in the streets, on the other side of town, Pfeiffer, Wynn, Mathon, and other disrupters from the earlier era gathered across town to commemorate a new milestone in Austin’s green building movement: its first-ever Green Awards. Fisk and Vittori hosted, and Fisk was in fine form, promising to keep making commotion.

One of the awards went to Capital Studios, a 135-unit building of efficiency apartments built on prime downtown real estate, two blocks from the state capitol. It was the first affordable housing built in downtown Austin in almost a half-century. All the apartments were rented out. The waiting list is a year.

View Images Kayakers paddle beneath the Lamar Boulevard Bridge on Lady Bird Lake. The quiet scene belies the boom in Austin, whose metro area is projected to double in population by 2030. “We have 100 people a day moving to Austin,” says Lucia Athens, the city’s sustainability officer. “We can’t afford to pause.” Photograph by Benjamin Rasmussen, National Geographic