The presidential race features unusually sharp contrasts by the candidates on whether to address rising temperatures.

The planet has already warmed beyond any point in human history. The election could determine if the next president will respond.

Global climate pollution is already starting to reshape the United States. In Phoenix, temperatures this year spent 70 days over 110 degrees. Hurricanes lashed the Southeast, with back-to-back storms killing more than 200 people. And cities across the continent choked on sickening smoke sent into the air by West Coast forest fires.

Americans have only just begun to respond to those changes. President Joe Biden took the strongest action yet of any president to address climate change, pumping $1.6 trillion into the economy to green power plants, vehicles and factories.

Now, the election is arriving just as those investments take hold. The outcome of the contest between Vice President Kamala Harris and former President Donald Trump could determine if they continue.

“There’s a lot of issues this cycle where the contrast is pretty goddamn sharp, like on abortion, for example, but climate change is one of those issues where the contrasts couldn’t be clearer,” said Leah Stokes, a professor at the University of California, Santa Barbara, who has advised the Biden administration. “One has a record of taking on big polluters, and the other one is in the pocket of big polluters.”

The two candidates are leading coalitions that could not be more different. Harris, who supplied the tie-breaking vote to pass the Inflation Reduction Act, offers continuity of Biden’s approach: massive renewable energy subsidies paired with some modest limits on fossil fuels.

Trump, who has long disparaged climate change as a “hoax,” has promised to supercharge the approach he took during his first term in office: unleashing oil and gas development, rolling back pollution rules and degrading federal support for renewable energy.

“The ocean will rise,” Trump said at a rally in Milwaukee on Friday. “Who the hell cares?”

In their only debate last month, Harris said Americans were already struggling with higher home insurance premiums due to extreme weather caused by climate change.

“I am proud that as vice president over the last four years, we have invested a trillion dollars in a clean energy economy while we have also increased domestic gas production to historic levels,” she said.

In the first Trump term, an internal “resistance” of career employees at agencies such as EPA slowed down his conservative agenda, said Steve Milloy, a lawyer who served on Trump’s EPA transition team in 2016. If Trump wins this time, anyone who slows down his priorities will be removed as a roadblock, Milloy said.

“The resistance got the better of Trump 1.0 in a lot of ways, and I think that people are wiser now,” he added. “There’s going to be a lot of work to do pretty quickly.”

The election is playing out amid the backdrop of a rapidly warming world. Global temperatures have risen by a little more than 1 degree Celsius compared to preindustrial levels. Scientists think the world has seven years at current emissions levels before global temperatures surpass 1.5 C and 28 years before temperatures exceed 2 C.

Eclipsing those thresholds comes with the risk of more frequent storms like Hurricane Helene, which smashed Florida with 140 mph winds and dumped more than 30 inches of rain on parts of North Carolina in late September. It would mean even higher temperatures than the ones experienced by Las Vegas last month, when the city recorded six days of triple-digit temperatures. Before then, the city had only experienced six days of 100 degrees in October — since 1937.

No matter who wins, the U.S. is not on track to meet the climate targets established by Biden. The president promised to cut emissions at least 50 percent of 2005 levels by 2030. But most forecasters think the U.S. will fall short of that mark, even as the country sets records for solar energy installations and electric vehicle sales.

“We unfortunately have to do a lot more because we’re not on track to meet the pollution goals that the Biden and Harris administration put forward,” Stokes said.

‘The IRA is just starting’

Enacting the IRA in 2022 represented the federal government’s first major attempt to get a handle on runaway climate pollution. The law was a departure from Democrats’ previous attempts to curb greenhouse gas emissions. Instead of regulating carbon pollution, the law hands out money to consumers and businesses to go green.

The approach partially reflected political realities. Democrats lacked a large enough majority in the Senate to pass non-budgetary measures. But it also pointed to a new theory of climate action.

“If a law includes a carrot, you immediately create a constituency that wants to preserve that. If a law includes a stick, you immediately create a constituency that wants to get rid of that law,” said Rep. Sean Casten, an Illinois Democrat who is outspoken on climate issues.

Two years later, the IRA boasts a complicated legacy. It has unleashed a wave of green investments. The country installed more utility-scale solar through the first nine months of 2024 (16.8 gigawatts) than every year except 2023, when it installed 19 GW, according to the Energy Information Administration. Electric cars reached nearly 9 percent of vehicle sales in the third quarter of 2024, a record. And businesses are exploring plans to make ammonia to power cargo ships, power steel plants with a blend of hydrogen and natural gas, and propel airplanes with low-carbon fuels.

Yet much of the law’s impact has yet to be felt. A POLITICO investigation found that manufacturers announced 555 factories to make clean energy technologies in the wake of the IRA’s passage. While 230 of those have announced plans to begin operations by the end of this year, fewer than half are up and running.

“The IRA is just starting to get implemented in the real world,” said Adrian Deveny, who helped author the IRA as a former aide to Senate Majority Leader Chuck Schumer. “A lot of that is because companies are waiting to see what happens. Companies are going to be very nervous making those investments if Trump wins because he’s promised to repeal the IRA.”

Although a Harris victory could safeguard the policies begun under Biden, her ability to expand climate action faces steep obstacles — especially if Republicans retain control over one or both chambers of Congress, as they’re favored to do.

If she lacks a friendly Congress to pass more climate laws, Harris’ ability to cut emissions through executive action would also face a skeptical Supreme Court, whose conservative majority has already flexed its power against climate rules.

Harris would “get handed an economy that’s midway through decarbonization, with a lot of open questions about who benefits and who doesn’t,” said Craig Segall, vice president of Evergreen Action, a policy and advocacy group.

In his first term, Trump dismantled much of former President Barack Obama’s climate legacy and installed industry lobbyists to head federal agencies. But many of his allies have said Trump came into office unprepared to weaken regulatory agencies.

This time would be different.

A new Trump weapon: The Supreme Court

Two key conservative groups, the American First Policy Institute and the Heritage Foundation, have spent years organizing an action plan with the goal of ensuring that government climate and clean energy policy is decimated for a generation.

A second Trump administration could also be prepared for a raft of lawsuits filed by environmental groups to slow down its agenda, Milloy said. There is a plan for that, he said, which involves setting “litigation traps.”

That means the Trump administration could try to get legal cases in front of the Supreme Court and its 6 to 3 conservative majority. Winning cases in the nation’s highest court could establish a legal backstop that would be used to go after even more regulations, he said.

“I think that’s going to change the courtroom battlefield a little bit, and I also think that Trump 2.0 will be a little smarter than Trump 1.0, so I think that the greens will be walking into maybe some litigation traps when they try to litigate this stuff,” Milloy said.

But Trump’s ability to hold back the energy transition would face real limits, too. Just like during his first term, when cheap natural gas helped cut U.S. emissions as coal-fired power plants shuttered, the economics of renewable energy and fossil fuels will shape how quickly the U.S. reduces climate pollution.

Weakening or destroying the Inflation Reduction Act is not the political winner that Trump thinks it is, said Ali Zaidi, Biden’s domestic climate adviser. He noted that House Republicans have unsuccessfully tried to repeal part or all of the law dozens of times, and a number of GOP lawmakers have called on Trump to preserve the law.

“I think that’s deeply unpopular, not just in the real world, but also in the bubble of Washington, where 50 votes have failed to achieve that goal in the House, and a dozen and a half House Republicans have sent a letter to the speaker saying, ‘Maybe we should stop trying to blow up our economic success,’” Zaidi said.

In a crucial battleground state, a top lawmaker said the stakes have already become clear to voters. Michigan’s aggressive climate laws were built on the IRA’s billions of dollars in climate funding, said Michigan House Speaker Pro Tem Laurie Pohutsky. When she’s canvassing voters, Pohutsky hears the issue breaking through: “It’s something that people on doors have been very, very excited about.”

“We’ve done historic, nation-leading work here in Michigan,” she continued. “And at the same time, we have our [Republican] counterparts who are refusing to even acknowledge that climate change is happening — while Michigan homes are flooding and we’re dealing with unprecedented weather events.”

“The comparisons,” Pohutsky added, “are really stark.”