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When Seattle Kraken fans take the city’s monorail to the hockey arena for home games, they don’t pay for the ride—a simple nudge that encourages them to leave their cars at home. When they arrive, their fried chicken is crisped inside fryers that run on electricity from renewable sources rather than gas. The dehumidifiers that keep mist from forming on the rink run on electricity too, as does the zamboni that resurfaces the ice, and the filtered water that comes out the back is collected from the stadium’s roof. Despite initial resistance from veteran journalists and managers, the game notes and statistics that were previously printed off at the end of each period are now emailed.

The Climate Pledge Arena, with its green ambitions raised from above by its environmentally-inclined owners and from below by Seattle’s eco-conscious populace, is an outlier. Its unparalleled commitment to sustainability earned it the title of the world’s first net-zero certified stadium last year. But it’s not alone. Around the world, sports venues and stadiums are taking similar steps.

This year’s Super Bowl host, Allegiant Stadium in Las Vegas, is aiming to run the event entirely off of renewable energy—a first in NFL history. The roof of the Johan Cruyff Arena in Amsterdam, home of soccer club AFC Ajax, is bedecked with more than 4,200 solar panels, which—alongside a wind turbine and a giant stadium battery—help keep the venue powered up. At the Mercedes-Benz Stadium in Atlanta, energy-efficient design reduces electricity usage by 29%, and fans are offered a free bicycle valet service on game days.

In 2008, Nationals Park in Washington D.C., home of the Washington Nationals baseball team, became the first stadium in the U.S. to receive the Leadership in Energy and Environmental Design (LEED) certification—one of the more commonly used sustainable building credentials. To do so, the stadium took a number of steps including installing energy-efficient floodlights and diverting 83% of its construction waste from landfill. Since then, over 60 more stadiums around the world, including over 50 in North America, have received LEED certification, according to data shared with TIME by the U.S. Green Building Council, the nonprofit that awards LEED certification.

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Sports venues are typically more forward thinking when it comes to sustainability than other sectors, such as commercial real estate, says Rhiannon Jacobsen, a managing director at the U.S. Green Building Council. Many factors account for this: Venues’ role as “trophy buildings,” which confers greater visibility and therefore increased scrutiny, the fact that public funds are often involved, and the need to make larger, more expensive buildings future-proof, she says.

But how much of a difference is this all making? There is no authoritative estimate for the climate impact of sports venues, or even of the sports industry more broadly. But there are clues. The Tampa Bay Rays franchise emitted roughly 35,900 metric tonnes of carbon in the 2019 MLB regular season—equivalent to the annual energy use of over 4,500 homes—70% of which was due to fan travel, according to an estimate from student researchers at University of California, Santa Barbara. The 2022 Fifa World Cup in Qatar generated an estimated 3.6 million metric tonnes of carbon—nearly equal to the annual emissions of a coal plant—of which travel accounted for 52% and construction accounted for 23%. Estimates like these are too scarce to stitch together to get a full picture, but they do give a sense of where the majority of sports-related emissions come from: construction and travel.

Regardless of what the actual figure is, any emissions reductions are better than none, says Rob Wilby, professor of hydroclimatic modeling at Loughborough University. “To really address climate change, every sector—not just sport, not just agriculture, not just energy, transport, whatever—every sector has to be making a difference,” Wilby says. “There’s no exemptions here if we’re really serious about tackling climate change.”

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The most obvious way to reduce emissions associated with construction is to avoid building new stadiums altogether. But less drastic steps can make a difference, too. The Climate Pledge Arena, for example, reduced emissions associated with construction by retaining the 44 million pound roof from the original Seattle Center Coliseum, which was built for the 1962 Seattle World’s Fair and designed by renowned architect Paul Thiry.

Travel-related emissions, meanwhile, can be difficult to cut, says Wilby. One potential solution is to adjust how tournaments are structured to reduce flight times as much as possible. For example, if an England soccer fan followed her team through all the qualifying matches and on to the finals of the 2022 World Cup, Wilby calculates that her travel-related emissions would be more than halved if the matches were arranged in a way that minimized zig-zagging around the world.

On top of these challenges, stadiums must ensure their efforts result in meaningful change—otherwise they risk being accused of greenwashing. For example, last month it was reported that the Intuit Dome, the future home of the Los Angeles Clippers that aims to be “the most sustainable arena in the world,” quietly backed out of deal with carbon credit trader Aspiration after U.S. regulators opened an investigation into whether the firm had misled customers about the quality of its offsets.

Highly visible measures that may have a smaller environmental impact compared to cutting construction and travel-related emissions can also play an important symbolic role. “These elements of waste and recycling might appear like chicken feed in the grand scheme of things,” Wilby concedes. “But when you then consider the power of sports to potentially influence behaviors, and then you scale it up across a whole at-home spectator group, then maybe if you change the behaviors of a small percentage of that mass audience, you’re having a more profound impact.”

Seattle Kraken fans certainly seem to be buying into the mission. On online forums, fans fastidiously question whether giveaways are compatible with waste reduction efforts and whether they can bring reusable cups into the venue. Internal surveys conducted last year of season ticket holders by Seattle Kraken’s marketing team showed that free public transit is the second most popular benefit after access to playoff tickets. And in April 2023, the arena organized a range of “green month” initiatives, including a bingo card of climate-friendly tasks such as taking the monorail to a game, the completion of which offered a chance to win free concert tickets.

“The ability for us, as an organization, to communicate with you, regardless of your income, your political beliefs, your race, or ethnic identity, the power for us to be a positive vision for ways in which we can tackle hard things together, unites people in a way unlike I’ve ever seen before,” says Rob Johnson, SVP of sustainability and transportation at Seattle Kraken and Climate Pledge Arena. “When we walk through the doors of that arena, we shed all that other tribalism, and we become one community. And that unifying moment is so powerful at trying to create positive change in our communities.”

Correction, Feb. 10

The original version of this story misstated the format of hockey games. Hockey games are divided into periods, not quarters.

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