Donald Trump’s reported decision to appoint a renowned climate change denier as the head of the US Environmental Protection Agency (EPA) has been condemned by environmentalists and scientists.

Dr Rush Holt, the chief executive of the American Association for the Advancement of Science (AAAS), compared disbelief in global warming to denying the existence of gravity.

And the Sierra Club, which claims to be the largest grassroots environmental group in the US with more than two million supporters, said the apparent decision to put Oklahoma state attorney general Scott Pruitt in charge of the EPA was “like putting an arsonist in charge of fighting fires”.

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The club, founded by renowned conservationist John Muir in 1892, is currently running a fundraising campaign urging people to join their cause and protect the planet from Mr Trump.

Mr Pruitt has said the science behind climate change is “subject to considerable debate” and has been hailed as a hero by deniers over his opposition to Barack Obama’s efforts to tackle the problem. He and a number of others filed a 28-state lawsuit against the Obama administration’s Clean Power Plan.

Michael Brune, executive director of the Sierra Club, said in a statement: “Having Scott Pruitt in charge of the US Environmental Protection Agency is like putting an arsonist in charge of fighting fires.

“He is a climate science denier who, as attorney general for the state of Oklahoma, regularly conspired with the fossil fuel industry to attack EPA protections.

“Nothing less than our children’s health is at stake. Scott Pruitt, whose own bio describes him as ‘a leading advocate against the EPA’s activist agenda’ cannot be trusted to head the EPA, an agency charged with protecting all Americans from threats to their water, air, and health.

“We strongly urge Senators, who are elected to represent and protect the American people, to stand up for families across the nation and oppose this nomination.”

Dr Holt, in a statement issued by the AAAS, also expressed concerns about Mr Pruitt’s appointment, saying the effects of climate change were already happening.

“The preponderance of scientific evidence and our understanding of climate change is rigorous,” Dr Holt said.

“Human activities are largely responsible, impacts are already underway, and the sooner we act, the lower the cost and risk will be.

“This has been well-established by many scientists working from many points of view and accepted by virtually every leading scientific organisation in the world. That clarity has continued to increase over the past three decades or so.”

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The statement said while the scientific process was inherently sceptical, it was “dangerous and counter to scientific methodology” to deny the existence of concrete evidence and theories that have proved robust for years.

The average global temperature of the world has risen by about 1C since the 1880s as the level of carbon dioxide in the atmosphere has risen because of the burning of fossil fuels. Simple experiments show carbon dioxide is a greenhouse gas.

This is accepted by some global warming sceptics such as Lord Lawson’s Global Warming Policy Foundation, who now subscribe to “luke-warmism”.

Dr Holt, who is the executive publisher of the leading academic journal Science, spelled out how far removed from the scientific evidence people like Mr Pruitt are in no uncertain terms.

“If a person jumped off a building because he said gravitation is only a theory, one would say he is delusional. So too, any policy maker who would base national policy on denial of climate science because there is ‘debate’ would be called dangerously irresponsible,” he said.

According to the AAAS’s What We Know report, the projected rate of temperature change for this century is “greater than that of any extended global warming period over the past 65 million years”.

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Scientists warned recently that climate change has already “passed the point of no return” but humans could still reduce the effects.

They said switching to renewable energy could avoid warming above 2C – beyond which it is believed storms, droughts and heatwaves could become dangerous across much of the planet – but failing to do this would see temperatures rise to 5C above pre-industrial levels.

Five degrees of warming would essentially be “game over” for human life as we know it with vast areas of the planet rendered uninhabitable, killing countless millions of people and forcing the rest to flee, making the current numbers of refugees fleeing war and extreme poverty in the Middle East and Africa look like a tiny trickle.

According to NASA, the 10 warmest years in its 134-year record have all occurred since 2000, with the exception of 1998. Last year was the warmest on record but 2016 is set to break that.

Sea ice in the Arctic and Antarctic has also reached a record low with an area the size of India melting.