MADRID — Presidential hopeful Mike Bloomberg called climate change “the greatest threat facing humanity” and told attendees at an international climate conference here that he would work aggressively to cut rising carbon emissions if he makes it to the Oval Office.

“The reason I am here in Madrid is really pretty simple: I am here because no one from the White House is here,” Bloomberg told an overflow crowd Tuesday, taking a shot at President Trump’s decision to withdraw the United States from the 2015 Paris climate accord.

The billionaire philanthropist arrived in town to unveil a new report on the extent to which sectors of the U.S. economy are on track to cut greenhouse gas emissions, even without assistance from the federal government. The analysis found that ambitious action on the part of cities, states and private businesses alone could reduce greenhouse gas emissions in the United States by as much as 37 percent below 2005 levels by 2030.

The study also determined that if the federal government worked to phase out coal power generation, provided incentives for electric vehicles and boosted the expansion of renewable energy, then the United States could cut its emissions nearly in half by the end of the coming decade.

Bloomberg’s appearance at the United Nations’ annual climate negotiations kicked off his push this week to highlight climate change as a central issue in his campaign.

This week, he put out an ad in California, titled “Smoke and Fire,” that calls Trump a “climate denier” who “consistently sides with polluters.” On Wednesday, he will address the American Geophysical Union’s annual conference in San Francisco.

Bloomberg, who entered the presidential race just last month, has been tapping his fortune to publicize his fledgling presidential bid. Rather than focus on the traditional early primary states, he is expanding operations in 27 other states and has spent more money on advertising than all the top-polling Democrats combined.

His campaign has said his first act as president would be to rejoin the Paris climate accord — a move he called a “no-brainer” Tuesday. Under that deal, the United States pledged to cut its emissions between 26 percent and 28 percent by 2025, compared with 2005 levels. Right now, the country is not on target to reach that goal.

Bloomberg, who has poured tens of millions of dollars into the Sierra Club’s campaign to shut down U.S. coal plants, made it clear he sees climate change as an existential threat that will require the full force of the federal government to join states, cities and businesses that are already transitioning away from reliance on fossil fuels.

“We could accomplish a lot more a lot faster if the federal government worked for us instead of against us,” he acknowledged, but added, “Regardless of what you hear out of Washington, the majority of American people support our Paris goals.”

He vowed to continue to pour his money and his time into addressing the problem.

“We have to have America as part of the solution, and I’m determined to try to make that happen,” he said. “Mother Nature doesn’t wait on any election calendar, so neither can we.”

Bloomberg and then-California Gov. Jerry Brown (D) launched America’s Pledge in 2017 as a counterweight to Trump’s move to unwind climate rules adopted under President Barack Obama and withdraw from the Paris agreement. The group, which published Tuesday’s report, quantifies climate actions by U.S. cities, states and businesses and works to ramp up action to help meet the nation’s promises under the Paris agreement.

During the past week and a half, the “U.S. Climate Action Center,” where Bloomberg spoke Tuesday — minutes after actor Harrison Ford told the crowd that “the antidote to despair is hope and collective action” — has been a hub of activity at the global gathering. A stream of local and state officials, faith groups, business leaders, academics and others delivered messages of unity in the absence of federal action on climate change.

The effort, organized by a collection of activist organizations, think tanks and philanthropic groups, has a simple and direct message: “We are still in.” Organizers describe the center as a constant reminder to other countries that while the United States might officially be on its way out of the Paris accord, plenty of other Americans remain committed to fulfilling its promises.

The findings Bloomberg highlighted Tuesday come a day after a separate report from a bipartisan coalition of more than two dozen U.S. governors, which found that their states are collectively on track to reduce emissions 20 percent to 27 percent below 2005 levels over the next five years.

The United States Climate Alliance, as the group is known, launched roughly two years ago. Its members represent more than half the nation’s population and 60 percent of its gross domestic product. States belonging to the group say they are reducing emissions and growing their economies more rapidly than the rest of the United States.

They say the benefits of curbing emissions extend beyond merely combating climate change. “Communities across these states have benefited from lower levels of harmful air pollutants; increased access to cheaper, cleaner energy; more efficient vehicles; and high-quality clean energy jobs,” the group wrote in announcing its report this week.

Separately, an international alliance of mayors, known as C40 Cities, highlighted the role that cities can play in leading efforts to mitigate climate change in a report released in Madrid. That group is also funded by Bloomberg.

“Cities are major contributors to the emissions that are causing climate breakdown,” Mark Watts, the group’s executive director, said in a statement. “But they are also where the solutions are being developed, tested and scaled up.”

Bloomberg regularly travels in a private jet, at a time when global emissions from the transportation sector are rising. Asked about the matter Tuesday, his campaign cited the massive sums of money and time he had spent focused on combating climate change during his tenure as New York’s mayor and more recently as a U.N. climate envoy.

“Mike Bloomberg has personally spent about $1 billion to flight climate change and encouraged an incalculable amount of donations and actions by others,” spokesman Stu Loeser said. “If he had spent that $1 billion instead on direct carbon offsets, it would offset more than 200,000 flights around the globe.”