Since the day last June when President Trump took to the South Lawn of the White House to declare his intention to withdraw our country from the Paris climate accord, more than 2,600 leaders from America’s city halls, state houses, boardrooms, and college campuses have signed the We Are Still In declaration.

This network includes 1,780 businesses and investors, nine states, 252 cities and counties, 213 faith organizations, and 339 colleges and universities. Together, they represent more than 130 million Americans and $6.2 trillion of the U.S. economy.

In an open letter to the international community, We are Still In declared, “We will continue to support climate action to meet the Paris Agreement….The Trump administration’s announcement ... out of step with what is happening in the United States.

“...It is imperative that the world know that in the U.S., the actors that will provide the leadership necessary to meet our Paris commitment are found in city halls, state capitals, colleges and universities, investors and businesses. Together, we will remain actively engaged with the international community as part of the global effort to hold warming to well below 2℃ and to accelerate the transition to a clean energy economy that will benefit our security, prosperity, and health.”

Signers include Walmart, the world’s largest retailer. Over 90 percent of Walmart’s carbon emissions footprint comes from primary production from their supply chain, and Walmart has invited all suppliers to join the retailer in a sustainability initiative (Project Gigaton) by eliminating one gigaton of greenhouse emissions by 2030. That’s equivalent to taking more than 211 million passenger vehicles off U.S. roads for a year. Walmart already gets about 25 percent of its global energy from renewable sources.

HP, one of two Fortune 500 companies created from the original Hewlett-Packard, is also on board. “Climate change is one of the most significant and urgent issues facing business and society today,” said Nate Hurst, chief sustainability and social impact officer, “and businesses must play a lead role in driving progress toward a circular, low-carbon economy.”

On December 4 in Chicago, 27 mayors signed the “Chicago Charter,” committing their cities to exceed the U.S. target under the Paris agreement and advance at least one specific climate action in their community in areas such as sustainable mobility, renewable energy, and green infrastructure.

They were followed in January by eight tribal nations from Oregon, Montana, California, and Washington. “Indigenous people around the world are working to address climate change, and it is our duty as Indigenous people of the Northwest to do our part,” said Leonard Forsman, chairman of the Suquamish Tribe of Washington.

The roster of colleges and universities includes Loyola University Chicago, which has issued a climate action plan, “A Just Future,” that lays out a path for achieving carbon-neutrality by 2025. Almost 1,400 of the university’s courses address sustainability issues, and since 2012 the undergraduate core curriculum has incorporated sustainability as part of scientific literacy. Since 2008 Loyola-Chicago has reduced its total carbon emissions by 38 percent per square foot of facility and now has 11 LEED-certified buildings, two geothermal installations, and 55,000 square feet of green roofs—more than any other Midwestern university.

Of course, the Partnership for Responsible Growth is still in, too. We are excited to see the commitment and creativity of the thousands who have joined We Are Still In and hope that their efforts will include support of a carbon fee. A large percentage of economists agree that such a fee is the most efficient, quickest, and most effective approach to climate change. A bonus benefit is that a national fee would generate a large revenue stream, part of which could devoted to infrastructure investments or other priorities or could help reduce our staggering national debt.

We have made this case in hundreds of visits to Capitol Hill offices, in a series of Wall Street Journal ads, in meetings with business leaders, and at a number of conferences, some of which we have organized. PRG also has been a leader in building a politically diverse coalition to champion a carbon fee.