It took until the last half hour of CNN's marathon three-hour Republican presidential debate, but global warming finally came up.

And apparently Republican candidates for president never got the memo that China is serious about addressing global warming.

In a question quoting Ronald Reagan's secretary of state, George Schultz, who favors "taking out an insurance policy" to guard against severe impacts of global warming, the candidates tripped over one another in a bid to be seen as the most skeptical on climate policy, while not saying anything too objectionable that would get them labeled a climate denier.

The way to do this, it seemed, was to say the U.S. can't go it alone on global warming, and wreck its economy, while China burns more coal.

Florida Sen. Marco Rubio said he opposes "left-wing" policy proposals to reduce greenhouse gas emissions, saying, "Every proposal they put forward are going to be proposals that will make it harder to do business in America, that will make it harder to create jobs in America."

Rubio said that having the U.S. take action against global warming would do nothing to alter the climate, since other countries would need to act as well.

Multiple economic studies have shown that left unchecked, global warming will cause trillions of dollars in damages to the U.S. over the next several decades, but far less if action is taken now to cut emissions.

In addition, Rubio failed to note that on Wednesday, about 40 miles down the road from the debate site in Simi Valley, high-ranking Chinese officials were meeting with U.S. governors, mayors and activists to take additional steps to reign in their carbon emissions, as part of the first annual U.S.-China Climate Leaders Summit.

The two-day gathering followed in the wake of an agreement President Barack Obama signed last year with Chinese President Xi Jinping, under which both countries agreed to take action to reduce their emissions. China and the U.S. are the top two emitters in the world.

That agreement, under which China pledged to peak its emissions by 2030 and radically scale up the use of renewable energy, has unlocked the door for a new, truly global climate treaty to be finalized in Paris in December.

It also presumably took the long-running talking point that the U.S. should not act until China does off the table.

Evidently not.

"America is not a planet," Rubio said, noting that China is exploiting fossil fuels around the world to fuel their development.

"And we are not even the largest carbon producer anymore, China is. And they're drilling a hole and digging anywhere in the world that they can get a hold of."

In the past, Rubio has presented himself as someone who questions the fact that the world is in fact warming due to human emissions of greenhouse gases such as carbon dioxide.

On CBS's Face the Nation in April, for example, Rubio said: "I do not believe in climate change in the way that some of these people out there are trying to make us believe."

For a bunch of people who don't believe in acting on climate change, the Republican candidates seem committed to recycling ideas. #GOPdebate — Hillary Clinton (@HillaryClinton) September 17, 2015

During the debate, though, Rubio seemed to shift that stance, instead focusing more squarely on policies to address the problem.

You can measure the climate. You can measure it. That's not the issue we're discussing. Here is what I'm skeptical of. I'm skeptical of the decisions that the left wants us to make, because I know the impact those are going to have and they're all going to be on our economy.

Los Angeles Mayor Eric Garcetti, left, Li Shixiang, executive vice mayor of Beijing, middle, and California Gov. Jerry Brown, clap during the U.S.-China Climate Leaders Summit in Los Angeles, Tuesday, Sept. 15, 2015. Image: Nick Ut/Associated Press

New Jersey Gov. Chris Christie came to Rubio's defense, saying, “I don’t think senator Rubio is a skeptic on climate change.”

Christie said the U.S. can't pretend that it can solve this problem alone, and can't take actions that would harm the country economically.

As governor, Christie pulled his state out of the Regional Greenhouse Gas Initiative (RGGI), which is a regional cap-and-trade program to cut emissions in the Northeast and Mid-Atlantic states, while using funds earned by the initiative to close the state's budget deficit.

According to the Star-Ledger newspaper, Christie's decision to abandon the climate program actually cost his state $114 million in lost revenue in 2011, and up to $387 million through 2017.

Christie said he disagrees with George Schultz, who is a distinguished fellow at the Hoover Institution at Stanford University, when it comes to acting on global warming, despite the fact that he worked in Reagan's cabinet.

“Everyone makes a mistake every once in a while, even George Schultz,” Christie said, while standing in front of Reagan's Air Force One.