On the most recent editions of CBS' Face The Nation and Fusion's America With Jorge Ramos, presidential candidate Sen. Marco Rubio (R-FL) was asked about his past remark that “I do not believe that human activity is causing these dramatic changes to our climate.” But while Fusion's Jorge Ramos made clear that Rubio's claim runs counter to the findings of 97 percent of climate scientists, CBS' Bob Schieffer did not.

During the April 19 edition of Face The Nation, Schieffer asked Rubio if he has said that “humans are not responsible for climate change.” Watch how Schieffer allowed Rubio to again deny the science of climate change with no pushback:

In contrast, when Rubio appeared in an interview that aired on the April 21 edition of Fusion's America with Jorge Ramos, Ramos emphasized that “97 percent of the studies on climate change say that you are wrong” :

Additionally, Fusion aired a segment immediately before the interview titled: “This is what America would look like if Marco Rubio was in charge.” In it, Fusion specifically refuted Rubio's false claim that there is no scientific consensus on whether the climate is “sensitive” to carbon emissions.

On both CBS and Fusion, Rubio peddled the misleading talking point that the climate is “always” changing. He added on Face the Nation: “The question is what percentage of that - or what is due to human activity.”

But the science is clear: human activities are the primary factor in climate change. The latest report from the United Nations' Intergovernmental Panel on Climate Change (IPCC) stated that “it is extremely likely that human influence has been the dominant cause of the observed warming since the mid-20th century.” The IPCC defines “extremely likely” as having 95-100% probability. And NASA agrees, stating: “Most climate scientists agree the main cause of the current global warming trend is human expansion of the 'greenhouse effect' -- warming that results when the atmosphere traps heat radiating from Earth toward space.”

It is becoming clear that journalists need to do a better job of pinning down the views of climate change deniers, particularly those with presidential aspirations. Press Think's Jay Rosen recently analyzed the different ways journalists choose to handle candidates who are climate changer deniers, and criticized The Washington Post for “normalizing” GOP presidential hopeful Sen. Ted Cruz's (R-TX) climate denial. Rosen also cited The New York Times' environmental editor Adam Bryant, who stated: "[C]laims that the entire field of climate science is some kind of giant hoax do not hold water, and we have made a conscious decision that we are not going to take that point of view seriously."

As David Roberts put it, “to reject mainstream government, academia, science, and media is to reject mainstream thought entirely.” When presidential candidates like Rubio engage in this kind of behavior, prominent media figures like Schieffer have a journalistic obligation to speak up.