RACHEL MARTIN, HOST:
Now that President Trump has announced his intention to pull out of the Paris climate accord, more cities around the U.S. are looking to cut their own carbon emissions. Hundreds of American mayors say they're committed to supporting 100 percent renewable energy. But is that really possible? As Grace Hood from Colorado Public Radio reports, it's complicated.
GRACE HOOD, BYLINE: In 2006, Aspen Utilities was one of the first in the country to declare a 100 percent renewable energy goal. Walking downtown, Mayor Steve Skadron points to the nearby mountain that supports the town's ski industry. As we pass designer stores like Prada and Gucci, he says behind the glitz is an environmental mission.
STEVE SKADRON: Put aside the crazy climate zealots telling everybody to sell their cars and eat tofu. It makes economic sense for us to support these values because our economy's based on the natural environment.
HOOD: Aspen had a good head start with hydroelectric plants like this one built in the 1980s. Dave Hornbacher directs Aspen Utilities.
DAVE HORNBACHER: As you can see here, it looks like a log cabin tucked into the woods.
HOOD: To get more renewable energy, the city wanted to revive another hydroplant on a different stream. It spent millions on the proposal. But some residents worried about the impact on the environment. In 2012, Aspen voters rejected the idea. Instead, Aspen signed contracts to bring in hydro, wind and biogas from other regions and states. In 2015, Mayor Skadron says that made the city utility the third in the nation to be powered completely by renewable energy.
SKADRON: It was really exciting. It was really hard.
HOOD: All that renewable power keeps the lights on downtown, but Aspen still uses natural gas to heat homes. And when you go to the ski resort or outlying homes, the power comes from a different utility that uses some fossil fuels.
JODIE VAN HORN: There are different factors that either enable or inhibit city's ease of achieving their goals.
HOOD: Jodie Van Horn directs a Sierra Club campaign that works with cities to use 100 percent renewables. Aspen wasn't part of this, but Van Horn says more than 30 places have signed on, including bigger cities like San Diego and Atlanta. The Sierra Club pushes cities to make their own renewable energy. But Van Horn says even when they buy energy from faraway places, like Aspen does, it has a wider impact.
VAN HORN: That city is helping to shift not just the electrons consumed within that community, but really helping the grid move towards cleaner sources of energy like wind and solar.
HOOD: The Sierra Club hopes all this will add up to lower carbon emissions for cities and the country. In Aspen, that's still a challenge. A decade ago, the city set out to bring down all its emissions 30 percent by 2020. Despite all its work, it's not there by a long shot. Mayor Steve Skadron has a new focus. He's talking with companies about tackling carbon emissions from cars.
SKADRON: Who's ever thinking about the transportation future, whether it's Tesla or Google or Ford Motor Company or Toyota or Apple, you know, they would bring the transportation future. And these conversations have started.
HOOD: After that, there's still airport emissions and the natural gas used to heat homes. The city hopes to issue a new climate action plan this fall. For NPR News, I'm Grace Hood in Aspen, Colo.
(SOUNDBITE OF BEASTIE BOYS' "KANGAROO RAT")
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