It would be fascinating to eavesdrop on discussions between members of the Flat Earth Society sailing the open sea, and debating why the horizon is curved. They would provide a good laugh.

They are deluded, but most committed flat earth believers appear normal in the rest of their lives and their delusion is not generally harmful to others.

A delusion is a belief that is clearly false, a denial of facts. It indicates an abnormality in the affected person's content of thought.

The false belief is not accounted for by the person's cultural or religious background or their level of intelligence.

The belief of climate change deniers is usually unshakable, like that of the flat-earth believers or Holocaust deniers. Many delude themselves that there is a conspiracy.

US President Donald Trump uses the words "hoax" and "Chinese hoax". Often their fervour leads to influential positions, for example in environment and energy policy as in the Coalition.

'The collapse of our civilisations'

Climate change delusion is dangerous to humanity, for it overtly or deviously prevents effective reduction of greenhouse emissions by governments in many countries, including the US and Australia, but is an increasing problem with the rise of right-wing governments in Europe and South America, including, Brazil where the new government has a foreign minister devoted to climate denial.

David Attenborough's warning will be understood by thousands of Australian children fearful for their future. ( ABC News: Jack Tegg )

Dangerous, for it is responsible for thousands of deaths worldwide from fire, flood, drought and hunger and a range of other causes including infections.

These deaths are projected to rise to 250,000 by 2030. In Australia the existing and expected health impacts are well documented and already affect our health services.

In the words of David Attenborough at C0P24:

"Right now, we are facing a man-made disaster of global scale, Our greatest threat in thousands of years, climate change... If we don't take action, the collapse of our civilisations and the extinction of much of the natural world is on the horizon."

These are words that many scientists have shunned to avoid being sensationalist, but which will be understood this week by thousands of Australian children fearful for their future.

To deniers, coal is clean, good, cheap

To the denier, there is no climate change — so coal is clean, coal is good, coal is cheap, it is our duty to export it to the poor of the world to give them electricity.

The denier's mind carries this absolution of coal beyond greenhouse emissions, to disregard the air pollution caused by coal. Outdoor air pollution is responsible for 4.2 million deaths a year around the world and many also in Australia.

In New South Wales, the five coal fired power stations are a health scourge from their pollution which causes 279 premature deaths, 233 babies born with low birth weight (less than 2,500g), and 361 people developing type-2 diabetes every year, who would not otherwise do so. These are preventable deaths and illnesses.

Yet government attempts to extend their use even when AGL provided a rational plan to close Liddell in five years and replace it with renewable sources of energy. The Coalition promotes more coal fired power, yet there is no safe level of air pollution.

One big lie often leads to another

Denial of climate change is unconscionable considering air pollution in NSW causes deaths, illness and large health costs. ( ABC News: Tim Leslie )

As Mr Trump and many of us have found, one big lie often leads to other lies and evasions to support it for example, in economics.

The Nobel Prize for economics this year was awarded to Professor William Nordhaus for his economic modelling of climate change. One conclusion from his work was that coal would have no added value to industry if the cost of its externalities of health, social and environmental, were accounted for.

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The Australian Government has to deny these facts to support a continuation of coal power, some denial for an economics-above-all government.

It is difficult to find the word "externalities" used by this government simply because it means coal is expensive in contrast to other modalities and their energy cost modelling collapses.

To doctors, this denial is unconscionable considering air pollution in NSW causes deaths, illness and large health costs, yet this appears to go unmentioned by any minister in the federal or state governments.

To address this world emergency our body politic needs massive reform in its thinking and governance.

Hopefully, the advice of one Minister to our young people demonstrating for their future — "I want kids to be at school to learn about how you build a mine, how you do geology, how you drill for oil and gas, which is one of the most remarkable scientific exploits of anywhere in the world that we do" — was the low point of this government.

Unfortunately, the Government tolerates climate deniers, so their constituents must instead vote them out to save lives.

Future climate policy must be guided by scientific expert opinion and removed from the vicissitudes of political chicanery by the implementation of new environmental laws which have application to health.

Dr David Shearman is the Honorary Advisor to Doctors for the Environment Australia and Emeritus Professor of Medicine at Adelaide University.