Hours after President Donald Trump announced last year that the United States would exit the Paris climate deal, a broad group of governors, mayors and business executives declared that they would uphold the agreement anyway and continue tackling global warming on their own.

It was a striking move for a coalition of local leaders: Making a case to the rest of the world that they, and not the president, spoke for the nation on climate policy.

To date, however, that groundswell hasn’t been nearly enough to counteract the effects of the Trump administration’s retreat on climate policy. Now, as many of those same local leaders and executives gather for a high-level conference in San Francisco this week, the group they created finds itself at a critical juncture, the moment when it shows whether or not it can rise to the task.

“Yeah, there’s pressure,” said Gov. Jerry Brown of California, one of the most visible faces of the movement, known as “We Are Still In.” State and local leaders “are carrying the flag while the big powers, the national guys, are rather somnolent.”

High-stakes meeting

The gathering in San Francisco, which is spearheaded by Brown, will bring leaders and civil society groups from around the world to discuss ways that states, cities and businesses can work together to reduce their emissions.

The stakes are high. So far, 2018 is on track to be the fourth-hottest year on record worldwide. Scientists are warning that countries have delayed so long in cutting emissions that many long-predicted disruptions from global warming are now unavoidable.

Against that backdrop, the Trump administration has been pushing to roll back many of the most prominent federal climate policies. Overseas, most national governments are falling far short of their promises to curb greenhouse gas emissions.

“We’re seeing signs of increasing apathy worldwide,” said Paul Bledsoe, a White House climate adviser under former President Bill Clinton. “And a lot of people are hoping that what’s happening in places like California could be the antidote.”

Heavy lifting ahead

Until now, local action on climate change in the United States has largely been led by a handful of blue states like California, the world’s fifth-largest economy.

On Monday, Brown signed a bill that would require California’s utilities to get 100 percent of their electricity from zero-carbon sources by 2045.

Other states — like Massachusetts, New Jersey, New York, Oregon and Washington — are racing to catch up.

Signs of climate action are sprouting at the municipal level, too. More than 70 cities have signed onto a goal of buying enough renewable power to offset all of their electricity consumption, though many mayors are now pondering how to pull that off.

And dozens of Fortune 500 companies including Google, Apple and Walmart have voluntarily invested billions of dollars into building new wind and solar farms.

Despite the flurry of state actions, though, the U.S. is still falling far short of its Paris Agreement pledges. A study in June by the research firm Rhodium Group estimated that the country was on pace to get only about halfway to former President Barack Obama’s promise under the pact to cut U.S. emissions at least 26 percent below 2005 levels by 2025.

One big reason for that: While many states have found it relatively painless to clean up their electric grids, swapping out coal for cleaner and cheaper natural gas and renewables, power plants are responsible for only about one-third of emissions.

A global approach

Brown stressed that the San Francisco conference was meant to be a global summit, and he is leading it with foreign representatives like Xie Zhenhua, China’s chief climate negotiator, and Anand Mahindra, a prominent Indian industrialist.

In effect, the leaders of We Are Still In are seeking to conduct their own version of foreign policy on climate change — forging partnerships with other local governments in countries like China to address global warming and urging leaders abroad to do more — at a time when the Trump administration has disengaged on the issue.

“It’s a new world,” said Jay Inslee, the Democratic governor of Washington. “We have the ability to work with the United Kingdom, as we have, with British Columbia, with Mexico, which we do. We can share best practices, we can look for investment opportunities. We are just not hampered by the Trump administration at all.”