On September 1st, the city of Boulder, Colorado joined a growing number of US cities in pledging to source 100% of its electricity from clean, renewable energy sources like solar and wind by 2030.

Boulder’s commitment is part of the Sierra Club’s #Readyfor100 campaign. Launched in January following the Paris climate agreement, #Readyfor100 encourages cities across the country to commit to transitioning to 100% renewable energy. In making this commitment, Boulder joins 16 other cities who have committed to sourcing 100% of their electricity from renewables, including San Francisco; Salt Lake City; Grand Rapids, Michigan; and Nassau, New York. In December, San Diego became the largest city in the U.S. to commit to 100% renewable energy, when it announced its plans to reach that target by 2035.

As Sierra Club’s #Readyfor100 campaign demonstrates, there is increasing momentum among cities to lead the way on climate action. The Global Covenant of Mayors for Climate and Energy, the world’s largest coalition of cities and local governments committed to climate leadership (created in June from the merger of two similar efforts), now has commitments from over 7,100 cities from 119 countries and six continents to take bold action to reduce emissions.

Around the world cities account for 70% of greenhouse emissions from energy, and local actions will be crucial in meeting international commitments to curb climate change. National commitments under the Paris Agreement will not be enough to limit warming to 2-degrees Celsius, the scientifically established limit to avoid the worst impacts of climate change. Of the remaining gap between agreed-upon commitments and the emissions reductions necessary to keep temperatures under the 2-degree limit, it is estimated that city and local actions can deliver a third of the needed cuts.

Boulder’s announcement was made at an event hosted by Sierra Club’s Rocky Mountain Chapter, Environment Colorado, Google’s Project Sunroof, and the Climate Reality Project, and brought together more than 30 groups and organizations encouraging other cities in Colorado to commit to 100% renewable energy.

In announcing the program, Boulder Mayor Suzanne Jones emphasized the importance of local action in reducing greenhouse gas emissions and framed the decision in terms of the climate change impacts Colorado is already experiencing: “Boulder is committed to achieving 100 percent renewable electricity by 2030, as part of our strategy to achieve 80 percent greenhouse gas emission reductions by 2050. Climate change is the issue of our time, threatening to fundamentally change the way we live our lives. We are already experiencing increasingly intense and frequent wildfires, declining snow packs, droughts and more extreme weather events. Yet, it is increasingly clear that Congress is not going to address climate change; cities like Boulder need to take the lead. We can act as a model for cities across Colorado to craft a sustainable future by shifting our energy model from the dirty fossil fuels of the past to clean, renewable energy.”

At the same event, the city of Denver, which has a goal of reducing its greenhouse gas emissions 80% by 2050, announced that it would explore how the city can make a similar transition. “We are committed to exploring efforts like 100 percent renewable electricity as part of our 80x50 process and look forward to having our partners here today help us take on this challenge, immediately initiating that work with a draft of results by mid-2017,” said Thomas Herrod, Climate & GHG Program Administrator of the City and County of Denver.

Boulder has long been a leader on climate action and this commitment is part of broader efforts by the city to reduce its emissions. Boulder’s current climate commitment, like Denver’s, seeks to reduce overall emissions 80% by the 2050. In 2007, Boulder adopted the country’s first voter-approved carbon tax. The “CAP tax,” levied on residents and businesses based upon the amount of electricity consumed, funded programs and services to reduce greenhouse gas emissions. These programs have helped keep Boulder’s carbon emissions relatively constant despite population growth, and the city estimates that they avoided more than 50,000 metric tons of emissions between 2007 and 2015.

Boulder is the second city in Colorado to make such a commitment. In 2004, Aspen announced its intention to supply its all of its electricity with renewable energy by 2015, and succeeded in making that target a reality last year. Several other U.S. cities, including Burlington, Vermont, Columbia, Maryland, and Greensburg, Kansas, have already made the switch to 100% renewable energy. These successes demonstrate the feasibility of powering our cities sustainably — and the power of local communities to lead the fight against climate change.