Under headlines that rang out across the world last week we read, "Evidence for man-made global warming has reached a gold standard level of certainty, adding pressure for cuts in greenhouse gases to limit rising temperatures".

A paper just published in the prestigious journal Nature shows that the certainty human activities are raising temperatures at the Earth's surface has reached a five-sigma level of confidence.

This is a statistical measure meaning there is only a one-in-a-million chance the signal would appear if there was no human intervention in the climate.


The science of climate change is solidly established, and its implications are taken seriously by governments and businesses around the globe. Of the 197 countries that signed the Paris Agreement 185 countries have now ratified it. There is no scientific basis for climate denial.

One of us (Michael Mann) writes in the book The Madhouse Effect that climate denial follows in the footsteps of earlier science denial, beginning with the long campaign by tobacco companies to confuse the public about the dangers of smoking. In the 1950s they already knew the links with cancer. Climate denialism resembles tobacco denialism.

Businesses with a financial interest in confusing the public — in this case, fossil-fuel companies — are prime movers in the campaign to spurn the obvious conclusion: we must reduce greenhouse gas emissions as quickly as is practicable.

A colourful cast of people, normally retired, have made a living out of denying the science of climate change. These so-called "experts" start out with, "I'm not a climate scientist, but ..." before launching into a series of carefully rehearsed talking points meant to confuse the public.

These people have been dubbed "the merchants of doubt" by science historians Naomi Oreskes and Eric Conway in their book of the same name.

As a recent paper showed, climate change poses a major threat to the nation. The unprecedented 2017/18 heatwave-like summer produced many adverse effects. These included the increased numbers of farmed fish dying, the grape harvest starting weeks early and the record loss of ice from our iconic glaciers in the Southern Alps.

Reliable climate records cover the four million sq km of marine and land surface temperature records of our Exclusive Economic Zone — the size of the Indian subcontinent — since the 1870s. These show at least a 0.8°C warming, with the warmest group of years centred on 2018. And the marine records are totally independent of the land surface air temperatures.

The major global reinsurance company Munich RE is very clear on the science of climate change and how it is increasing risk. Insurance is the business of risk, and the insurance sector is in no doubt what it is up against.


Munich RE shows and documents there has been more than a doubling of the number of weather and climate related natural disasters worldwide since the 1980s. We don't see articles explaining Earth is flat and moon landings are a hoax or denying the Holocaust. So why climate denial?

The BBC has adopted guidelines on their climate-change coverage and agreed:

1. Man-made climate change is real and the most widely accepted view on the science is that of the Intergovernmental Panel on Climate Change (IPCC). It is accepted by at least 97 per cent of scientists working and publishing in the field.

2. Because there is such a powerful consensus, there is no requirement to give climate deniers a platform. A debate with one expert scientist versus one denier demonstrates a false balance; to get a genuine balance you would need at least 97 scientists for every three deniers.

3. There might be occasions where contrarians and sceptics could be included in debates. For instance, discussing the speed and intensity of what will happen in the future, or what policies government should adopt to mitigate the problem and adapt.

These guidelines are not shutting down debate but are creating space for the difficult and terribly important question of how to respond to climate change.

As another example, media stopped stories on how HIV didn't cause AIDS and concentrated on what to do to stop the spread of the virus and support those already infected.

The World Economic Forum in 2018 rated extreme weather events, natural disasters and failure to act on climate change as the most important risks for the globe. The pressing question is not whether climate change exists: the problem is staring us in the face. The question that really matters is what we do about it.

To allow climate denial is totally irresponsible for the general public and particularly for our children and grandchildren.

Dr Jim Salinger is a Visiting Scholar at Pennsylvania State University where Distinguished Professor Michael Mann is Director of the Earth Science System Center.