Jim Brainard is keeping a promise that the United States broke.

Brainard, mayor of Carmel, Indiana, a suburban city just north of Indianapolis, has pushed his town to make a variety of changes to reduce its greenhouse gas emissions. City vehicles are now hybrids or run on biofuel. About 800 streetlights have been retrofitted with LED bulbs. Roundabouts in 122 intersections replaced traffic lights, a change that means cars don’t burn gas while idling at a stop.

“Of course, it would be ideal to set some national standards, but a lot of regulation on things that impact the environment is done at the state and local level, so we can have a huge impact,” he said.

Brainard is part of a growing coalition of leaders at the city, state and business levels who have remained committed to reducing carbon emissions in line with the Paris Agreement, despite President Donald Trump’s announcement in 2017 that he plans to quit the climate accord.

Those efforts are making a difference. A new report released Monday by America’s Pledge, a climate-focused research initiative launched in 2017, found that the actions of cities, states and businesses can add up.

The report comes as world leaders gathered in Madrid this week to reassess the goals set out in the Paris Agreement, including how to ramp up reduction efforts.

The report found that the We Are Still In coalition, a group of 3,800 mayors (of which Brainard is one), county executives, tribal leaders and businesses that account for more than half of U.S. greenhouse gas emissions, could reduce emissions 25 percent below 2005 levels by 2030 with climate policies that are already in place.

While that falls short of the United States’ original Paris pledge, which was calculated in order to keep warming below 2 degrees Celsius (3.6 degrees Fahrenheit) by the end of the century, it represents an encouraging baseline, said Nathan Hultman, director of the Center for Global Sustainability at the University of Maryland in College Park, and one of the authors of the America’s Pledge report.

“It’s still remarkable that we can get to a 25 percent reduction with these policies,” said Hultman, who worked on climate and energy policy as part of the Obama administration from 2014 to 2016. “What this tells us is we need a lot more action and a lot more rapidly than what’s on the books today from cities, states and businesses.”

The budding coalition represents a grassroots approach to climate policy that experts say could be crucial to keeping the country’s Paris accord pledges within reach. And it has some bipartisan support.

Brainard is a Republican, and Carmel lies at the heart of one of the 10 largest coal-producing states in the country. As the mayor of a red city in a red state that has long been a Republican stronghold, he said that climate action is not at odds with his politics.

“The root of the word ‘conservative’ is ‘conserve,’” Brainard said. “Why would you want to recklessly disregard what scientists are saying about the environment if you are a conservative?”

He maintains that climate solutions should transcend party lines. “I’ve yet to meet a Republican or Democrat who wants their family to drink dirty water or breathe dirty air or leave the planet uninhabitable,” he added.

As part of the 2015 Paris Agreement, which has since been ratified by 187 countries, former President Barack Obama pledged that the U.S. would reduce greenhouse gas emissions 26 to 28 percent below 2005 levels by 2025.

But climate researchers say there are some parts of climate policy that need federal support to be most effective.

“If the federal government continues to occupy the posture that it’s in right now, the message to individual households or corporate decision makers is that the choice they are faced with is ambiguous,” said Jonathan Elkind, a senior research scholar at the Center on Global Energy Policy at Columbia University in New York City.

The America’s Pledge report also noted that in the event that the 2020 election results in an administration that supports ambitious climate action, that number could jump to a 49 percent reduction below 2005 levels by 2030.

“We recognize that if we have an administration and a Congress that supports climate action, we could see a comprehensive U.S. climate strategy that layers an ambitious set of federal policies on top of leading state and city policies,” Hultman said.

But even without federal backing, states and cities can make significant progress on their own, particularly if local leaders face pressure from their electorate, according to Pam Kiely, the senior director of regulatory strategy at the Environmental Defense Fund, a nonprofit advocacy group headquartered in New York City.

“There is a real opportunity right now because there has been a phenomenal focus on climate change, driven by youth demanding big changes, but also many other people who are fed up with inaction on this crisis,” Kiely said.

Most states in the country have expansive authority to tackle and reduce air pollution and greenhouse gas emissions, she said.

In California, for example, a cap-and-trade program introduced in 2013 used a market-based approach to reduce air pollution by limiting the state’s total emissions and allowing industrial companies to purchase pollution “allowances.”

The program aims to reduce the state’s emissions to 40 percent below 1990 levels, and last year generated $1.4 billion that was reinvested in green initiatives such as installing solar panels and providing incentives for electric cars. Oregon Gov. Kate Brown is looking to implement a similar policy framework, and the California cap-and-trade program has been held up as a model for other states and countries around the world.

States can also make significant investments in clean energy, electric vehicles and infrastructure, according to Elkind. And at the city level, local leaders can influence building codes, zoning laws and transportation systems, he added.

But other areas, such as the industrial sector, will be much more challenging to decarbonize, Kiely said. What’s more, support from the federal government is integral for sweeping initiatives and investment in research and development for new technologies and innovative approaches to fighting climate change.

“There is a tremendous amount that can be done at the city and state level, but I don’t think there’s a world in which it makes sense for the federal government to continue to sit on the sidelines,” she said. “We absolutely need to get back to a place where the U.S. is leading on climate action and we have a comprehensive federal strategy.”

And federal support will be critical for showing the global community that the U.S., the second-largest emitter of greenhouse gases, is doing its part to combat climate change, Kiely said.

Yet, Elkind said the actions of cities, states and businesses are significant, and the implications should not be discounted.

“We can’t underestimate or trivialize the significance of states and localities saying: ‘we are still in,’” he said. “That alone should give a strong signal to people around the globe that there’s a bitter dispute unfolding in the United States right now over the right way to handle climate change, and that there are still hundreds of thousands — even millions — of people who are dead set on doing the right thing.”