Earlier this year, a group of Florida mayors that are dealing with problems caused by sea level rise sent a letter to the Republican presidential candidates that hailed from the same state. "We call on you to acknowledge the reality and urgency of climate change," the letter said. But Jeb Bush and Marco Rubio, both of whom have been ambiguous at best about that reality, ignored the letter.

With Bush since departing the race, it was left to Marco Rubio to field that request at last night's Republican debate in Florida. "Senator Rubio, the Miami mayor has endorsed you," moderator Jake Tapper noted. "Will you honor his request for a pledge and acknowledge the reality of the scientific consensus of climate change and pledge to do something about it?"

Rubio's response distilled down to "no," but he made a complete hash of its details.

"Well, sure if the climate is changing and one of the reasons is because the climate has always been changing," Rubio responded. "There's never been a time when the climate has not changed." He went on to say that one of the questions a policymaker must ask is whether the climate is changing because of something we're doing.

The first part of the answer is a standard talking point—if the climate has changed in the past without human influence, why should we think that humans are changing it now? It's the equivalent of asking why, if forest fires occurred before humans were around, we should think any forest fires are caused by humans. The most disappointing thing about this non-answer, however, may have been that Rubio was interrupted by applause when he gave it.

As for whether it's something we're doing, the Intergovernmental Panel on Climate Change has built an extraordinarily comprehensive case that it is.

The remainder of Rubio's answer was largely an argument for doing nothing. Regarding the plight of the Florida mayors, Rubio said, "If there is higher sea levels or whatever it may be happening, we do need to deal with that through mitigation." In other words, try to deal with ensuing problems as they occur rather than addressing the root cause. Rubio was not asked to clarify how low-lying coastal islands could mitigate their way out of the meter or more of sea level rise that now seems inevitable.

He also argued against acting on economic grounds, saying, "There are laws they want to us pass that would be devastating for our economy." But that assumes that carbon-emitting energy sources have remained the most economic, which is no longer true.

Finally, Rubio argued that the US acting while other countries continue emitting would make our actions pointless. This argument is somewhat questionable, as it's clear that the initial pushes toward renewable power here and overseas are what helped drive the costs of renewable power down so quickly. But this also would appear to be an argument for international agreements to cut emissions—an issue that never came up. Instead, Rubio summarized his position by saying, "I am not going to destroy the US economy for a law that will do nothing for our environment."

At that point, the question was handed over to Ohio governor John Kasich. "I do believe we contribute to climate change, but I don't think it has to be a, you know, either you're for some environmental stringent rules or, you know, you're not going to have any jobs," Kasich said. "The fact is, you can have both." He then touted a variety of approaches that have allowed his state to cut emissions by 30 percent.

Kasich wasn't fully on board with the scientific consensus, however. "We don't know how much humans actually contribute," he said. (We have a pretty good idea, if not a precise percentage.) And Kasich advocated for clean coal, a technology that doesn't currently exist.

Still, the two candidates offered a stark contrast in terms of both economic and scientific realities. None of the remaining candidates were asked for input on the topic, but past statements suggest that they would lie on Rubio's end of the spectrum—and perhaps be even more extreme.