May 12

SEN. MARCO Rubio (Fla.), whom many presume to be a contender for the 2016 Republican presidential nomination, said two things Sunday about climate change. Only one could fit into a presidential campaign worth taking seriously.

Our climate is always changing,” he said on ABC News’s “This Week.” “I do not believe that human activity is causing these dramatic changes to our climate the way these scientists are portraying it,” he went on to say, “and I do not believe that the laws that they propose we pass will do anything about it, except it will destroy our economy.” In previous interviews, at least Mr. Rubio acknowledged that “a significant scientific consensus” attributes measured global warming to human activity before he lodged various criticisms.

It is one thing to invite a debate about the best policy to address rising global temperatures, a problem no country can tackle on its own. It is another to dismiss the evidence that “these scientists” have compiled — “a handful of decades of research,” Mr. Rubio derisively called it — to show that humans are driving much of that warming.

Just last week, a fresh federal analysis articulated anew many of the reasons the debate should focus on how to respond to the threat of human-induced climate change, not on whether it is happening. The research, a large panel of experts concluded, “tells an unambiguous story: the planet is warming, and over the last half century, this warming has been driven primarily by human activity.”

Scientists rely on “multiple lines of independent evidence” to reach that conclusion. Beyond the basic physics that more greenhouse gases in the air will tend to intensify the greenhouse effect, researchers can’t explain the temperature record of the past 50 years without adding human influence to the picture. Then there are observable climate “fingerprints,” such as where warming is happening, both on the Earth and in the atmosphere, that implicate human-released greenhouse emissions as a major culprit.

Scientists know that the climate changes naturally, too. “Human-induced warming is superimposed on a background of natural variations in climate,” the federal assessment noted. But other possible drivers, such as changes in the sun’s output, can’t fully explain the warming the planet is seeing. Volcanic eruptions and other factors, they reckoned, would have cooled the Earth if not for human activity reversing that course.

On Sunday, Mr. Rubio insisted that he is ready to be president. We hope he does not count sidling up to climate change denial as a qualification. It is quite the opposite.