Scott Pruitt, the climate science-denying head of the US Environmental Protection Agency, has claimed that human activity is not a “primary contributor” to global warming.

Appearing on the CNBC TV show Squawk Box, Mr Pruitt, a lawyer, was asked if he thought it had been proven that carbon dioxide was the “primary control knob for climate”.

While the biggest input to the Earth’s temperature is obviously the sun, rising levels of carbon dioxide and other greenhouse gases have been increasing the atmosphere’s ability to trap its heat and this is the main reason why temperatures have risen by about one degree Celsius since the late 19th century.

Nasa, the UK Met Office and ever single major scientific body worldwide agrees this is true. The process by which carbon dioxide acts as a greenhouse gas has been understood for more than a century and can be demonstrated by a simple experiment.

However Mr Pruitt, chosen by Donald Trump to run an agency he made a career out of repeatedly suing as the attorney-general of Oklahoma, told CNBC: “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 it's a primary contributor to the global warming that we see.

“But we don't know that yet as far as ... we need to continue the debate and continue the review and the analysis.”

A common tactic used by climate science deniers is to try to exploit the language and nature of science to suggest global warming is simply 'a theory' and that there is still 'debate' about the issue. It may be that Mr Pruitt was attempting to follow this line but inadvertently over-stepped into outright denial of accepted science.

Rush Holt, the chief executive of the American Association for the Advancement of Science, has compared denying climate science to disputing the theory of gravity.

And even Lord Lawson's climate sceptic think tank in the UK, the Global Warming Policy Foundation, accepts carbon emissions have caused the Earth's average temperature to rise.

Asked by The Independent to comment on Mr Pruitt's remarks, climatologist Dr Gavin Schmidt, director of Nasa's Goddard Institute for Space Studies, wrote: "I'm on record (as is Intergovernmental Panel on Climate Change, [US] National Academies, [UK] Royal Society etc) as saying that all recent warming is essentially anthropogenic and the dominant factor is carbon dioxide."

This essentially restates the message of a joint statement issued by Nasa and the US National Oceanic and Atmospheric Administration in January.

It said the latest figures showed Earth’s average surface temperature had risen by about 1.1 degrees Celsius since the late 19th century. The UK Met Office produced similar figures based on different measurements at around the same time.

This was, the Nasa/NOAA statement said, “a change driven largely by increased carbon dioxide and other human-made emissions into the atmosphere”.

“Most of the warming occurred in the past 35 years, with 16 of the 17 warmest years on record occurring since 2001,” the statement added.

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“Not only was 2016 the warmest year on record, but eight of the 12 months that make up the year – from January through September, with the exception of June – were the warmest on record for those respective months.

“October, November, and December of 2016 were the second warmest of those months on record – in all three cases, behind records set in 2015.”

Not all of the temperature rise was attributed to greenhouse gases resulting from human activity.