SAN FRANCISCO — Thousands of mayors, climate activists and business leaders from around the world descended Thursday on San Francisco to cheer on efforts to reduce global warming, even after U.S. President Donald J. Trump signaled his disdain for the issue.

The Global Climate Action Summit, sponsored by California Gov. Jerry Brown, included a report that 27 major cities around the world have seen emissions decrease over a five-year period and are now at least 10 percent lower than their peak.

The cities include Berlin, London, Los Angeles, New York, Paris and San Francisco. Together the cities include about 54 million people.

The report came from C40 Cities Climate Leadership, a group whose board is headed by philanthropist and former New York City mayor Michael Bloomberg.

In a speech, he called the conference a way to broadcast that the U.S. is still committed to fighting global warming.

"Climate change is a global challenge and Washington ought to be leading from the front," Bloomberg said.

Many people around the world wrongly concluded that America was "walking away from climate action" when Trump pulled the country out of the Paris climate accord, but "nothing could be further from the truth," he said.

The 2015 Paris agreement commits countries to set their own plans for cutting emissions.

Bloomberg and Brown, a Democrat, said they calculate the country is within striking distance of the reduction in greenhouse gases previously promised by the U.S.

Trump announced last year that he was withdrawing from the landmark climate accord. His administration is also pursuing policies that would boost methane emissions and roll back California's strict vehicle emissions standards.

In response to a question Thursday at a news briefing, Brown said Trump will likely be remembered poorly when it comes to the environment.

"I think he'll be remembered, on the path he's now? I don't know. Liar, criminal, fool," the governor said.

The CEO of Salesforce, one of the world's largest online business software companies, urged fellow technology leaders at the conference to help fight climate change.

CEO Mark Benioff announced that Salesforce and 20 technology companies have signed a pact to "decarbonize" by reducing greenhouse gas emissions worldwide through supply chains, regulations and customer efforts.

Salesforce recently opened a 61-story office tower in San Francisco that it says relies on clean energy to operate.

Outside the conference, hundreds of protesters claimed Brown could do more in California, and about a dozen briefly interrupted Bloomberg's speech with chants that the land and air were not for sale.

Protesters also called on Brown to ban the practice known as fracking, which injects high-pressure liquid into the ground to extract gas.

In response, the governor reiterated his ambitious goals for battling greenhouse gas emissions at all levels.

Bloomberg chimed in: "America's a wonderful country. Here we have environmentalists protesting an environmental conference."

Summit spokesman Nick Nuttall said he is not aware of any U.S. government officials attending the event. Messages to the U.S. Department of Interior, National Oceanic and Atmospheric Administration and Environmental Protection Agency were not returned.

The summit came with 2018 on pace to be the fourth hottest year on record globally.

The eight warmest years in more than a century of record keeping have all been in the past 13 years.