Climate deniers love to repeat this dead wrong talking point. Here's how to refute it.

On Sunday morning, CNN anchor Jake Tapper asked U.S. Senator Marco Rubio whether he thought the changing climate on Earth today was “at least in part” caused by humans. 

On live television, Rubio acknowledged that humans were partly responsible, and then immediately sowed some doubt into his answer.

“I think many scientists would debate what percentage is attributable to man versus normal fluctuations,” Rubio said. 

This is misleading, at best, because there is no plausible debate. 

In a variety of ways, scientists globally have repeatedly shown that the modern-day warming of our oceans and atmosphere is specifically attributed human activity — not volcanoes nor the sun. We’ve simply loaded the atmosphere with carbon-based gases that physically trap heat.  

“The actual science indicates that climate change is responsible for all of the warming of the planet over the past century,” Michael Mann, a climate scientist at Penn State University, said over email.

Other natural factors — notably energy output from the sun and gases emitted from volcanoes — have in total actually gone in the opposite direction, noted Mann, even causing a minor amount of cooling, but certainly not enough to make a dent in the warming trend.

The scientific consensus about human responsibility for climate change is now staggering. 

The notion that prominent politicians continually still question the attribution of our warming globe — and sometimes even the political motivations of scientists — is growing increasingly far-fetched, or simply absurd.  

“Anyone who knows science knows that trying to get a lot of scientists to agree on something is like herding cats,”  Stefan Rahmstorf, head of Earth System Analysis at the Potsdam Institute for Climate Impact Research, said over email.

“The idea that many thousands of climate scientists, from all continents and all kinds of upbringing and political systems and persuasions, are all driven by the same political agenda, is the most silly conspiracy theory that I have heard,” added Rahmstorf. 

“There is a much simpler explanation for the overwhelming consensus among climate scientists about human-caused global warming: The scientific evidence for it is overwhelming.”

SEE ALSO: Climate change could threaten the world’s beer supply. Do you care about global warming now?

Scientists have a keen understanding of how much energy from the sun enters the Earth, as well as the amount of greenhouse gases volcanoes contribute to the atmosphere. These natural sources simply can’t explain accelerated, modern-day warming.

What’s more, climate scientists have a good record of the how much industrial activity and land clearance — which removes forests that suck carbon out of the air — has occurred globally since the Industrial Revolution began, Jonathan Overpeck, a climate scientist at the University of Michigan, said over the phone. 

“We know that the carbon dioxide in the atmosphere is from human activity, primarily burning of fossil fuels and clearing of land, for a variety of reasons, all confirming each other,” emphasized Overpeck.

A prominent chunk of evidence is that the carbon in the air carries a telltale chemical signature.

“The chemical composition of the air has changed, and it’s a fingerprint that reveals it has to be changing because of fossil fuel burning and land clearance — cutting down the forests,” he said.

There are two stable types of carbon, called isotopes, that naturally exist on Earth, a heavier and lighter type.

“Plants like to consume the lighter isotope,”  Kristopher Karnauskas, a professor in the Department of Atmospheric and Oceanic Sciences at Colorado Boulder, said in an interview.