Scott Pruitt, head of the Environmental Protection Agency under US President Donald Trump, has denied a basic scientific fact known to the majority of teenagers.

Appearing on CNBC on Thursday (9 March), the 48-year-old said that he did not believe that carbon dioxide emissions are a primary cause of global warming.

Pruitt has repeatedly been labelled as a "puppet of the fossil fuel industry" for his career-long attacks on the regulatory body he now heads and for his climate-science-denying views, but his latest comments appear to be the furthest he has ever gone.

"I think that measuring with precision human activity on the climate is something very challenging to do, and there's tremendous disagreement about the degree of impact, so, no, I would not agree that [carbon dioxide emissions are] a primary contributor to the global warming that we see," he told CNBC.

"But we don't know that yet ... We need to continue the debate and continue the review and the analysis."

Pruitt's comments are at odds with his own department, which states that CO2 is the "primary greenhouse gas that is contributing to recent climate change".

The process of global warming and the greenhouse effect has been understood and agreed upon by a majority of scientists for over a century.

After sunlight reaches Earth, it can be reflected back into space or absorbed by the Earth's surface. Greenhouse gases such as CO2 and methane absorb that heat energy and prevent it escaping into space, gradually warming our environment like a blanket.

Not understanding this basic science makes Pruitt incapable of heading the EPA, scientists have said.

Kevin Trenberth, a distinguished senior scientist at the National Center for Atmospheric Research, said: "Pruitt has demonstrated that he is unqualified to run the EPA or any agency.

"There is no doubt whatsoever that the planet is warming and it is primarily due to increased carbon dioxide in the atmosphere from burning of fossil fuels."

Richard Somerville, research professor at Scripps Institution of Oceanography at the University of California, San Diego, said: "Our burning of coal, oil and gas is the dominant cause of the 45% increase in CO2 since the industrial revolution.

"The biggest unknown about future climate is human behaviour. Everything depends on what people and their governments do."

Pruitt has received over $300,000 in donations from fossil fuel companies since 2002 and emails leaked in January showed his intimate relationship with giant energy corporations such as those linked with the Koch brothers and Devon Energy.