Greta Thunberg and Extinction Rebellion have been raising awareness of the urgent need to stop talking and start acting on global warming. The evidence that global warming is real and that it is human-caused is now overwhelming, but the public debate is regularly swamped by science deniers who in most cases clearly simply ignore or are ignorant of the evidence, and often are clearly clueless about how to assess evidence, or even what constitutes evidence.

The first illustration below, from a recent Economist issue, summarises the rise in average temperature across the earth’s surface in 2018 compared to the average for 1951-1980.

Many deniers claim that the current rising temperature is natural, resulting from ice age cycles or orbital variations of the earth. The graph below shows how current CO2 levels are dramatically higher and rising faster than in any interglacial period over the last half million years. And our best climate models predict temperature rises associated with CO2 levels which match measured temperatures over the last 40 years. If the impact of CO2 is excluded from the models, it is not possible to explain the observed rise in temperature (see graph below).

Three recent studies published in Nature and Nature Geoscience use extensive historical data to show there has never been a period in the last 2,000 years when temperature changes have been a s fast and extensive as in recent decades (Neikom1, Neikom2 ,Bronnimann ).

It had earlier been thought that similarly dramatic peaks and troughs might have occurred in the past, including in periods dubbed the Little Ice Age and the Medieval Climate Anomaly. But the three studies use reconstructions based on 700 proxy records of temperature change, such as trees, ice and sediment, from all continents that indicate none of these shifts took place in more than half the globe at any one time.

The Little Ice Age, for example, reached its extreme point in the 15th century in the Pacific Ocean, the 17th century in Europe and the 19th century elsewhere, says one of the studies. This localisation is markedly different from the trend since the late 20th century when records are being broken year after year over almost the entire globe, including this summer’s European heatwave. Major temperature shifts in the distant past are also most likely to have been primarily caused by volcanic eruptions, according to one of the three studies.

The oft-quoted 97% figure

In the last few days I have seen several articles quoting the claim that 97% of climate scientists accept that humans are causing global warming.  This figure actually comes from a 2013 article in Environmental Research Letters by Cook et al. titled “Quantifying the Consensus on Anthropogenic Global Warming in the Scientific Literature”. It actually estimated that among abstracts expressing a position on global warming, 97.1% endorsed the consensus position that humans are causing global warming”.  Not a per cent of scientists but a per cent of papers whose abstracts expressed a position. But the misquote has achieved the status of a universal factoid trotted out by those arguing that humans are causing global warming as well as climate sceptics, who point to 3% thinking it is not real means there is uncertainty.

A more recent review of abstracts from 2013 and 2014 (the_consensus_on_anthropogenic_global_warming) found that of 24,210 abstracts of papers on climate change, only five explicitly rejected human role in global warming. As two of these papers were by the same author, the final figure for scientists who publish on global warming and reject a human causative role is 1 in 17,352 or 0.006%. Almost certainly this percentage is even lower now as more evidence floods in every year. This is probably as close to unanimity as humans are capable of in areas of science that involve such massive amounts of data of different kinds.  Its probably approaching the level of unanimity among physicists and geologists about the shape of the earth. In that case, the evidence is also overwhelming but quite straightforward and accessible to anyone. I suspect the number of scientists publishing papers arguing the earth is flat is actually a real zero per cent.

The obfuscation and undermining of science

In a recent post (are-humans-heating-up-the-world), I commented that the climate change denial is being fuelled by deliberate obfuscation and funding of deniers, politicians and right-wing think thanks, that is reminiscent of the way that tobacco companies set out to confuse and obfuscate the very clear scientific consensus. And I went even further to say that in both cases, the relevant industries knew the truth from quite early on but hid that.  After I posted it, I had some qualms. While I thought I was right, perhaps I was just remembering second hand comments and I should check my facts. So I did.

Cummings et al have documented the evidence that the tobacco companies knew and for most part accepted the very strong evidence that cigarette smoking was a cause of cancer by the late 1950s. They and Brandt also document how the tobacco companies’ response was to deliberately undermine the acceptance of the facts by funding research intended to obfuscate the debate about smoking and health and to manufacture controversy about the facts.

In the immediate post-war years – the dawn of the nuclear age – science was in high esteem. Scientific advances (the bomb, radar, computing) had played a major role in winning the war, and continued to transform everyday life with radio, TV, electronics and electrical labour-saving devices. The tobacco industry launched an unprecedented strategy to undermine acceptance of scientific results through funding research intended to undo and obfuscate what was known. In doing so it provided substantial funding to researchers and doctors who would work to confuse the public and more or less invented the modern conflicts of interest that are now such a source of contention in science, medicine, media and public policy. This strategy of producing apparent uncertainty in the science (which actually largely did not really exist) undercut public health efforts and regulatory responses designed to reduce the harms of smoking.

Following the publication by Sir Richard Doll and Austin Bradford Hill in 1952 of a definitive review American, German and British studies which showed smoking was an important cause of lung cancer, the major tobacco companies of the time commissioned a public relations company, Hill and Knowlton, to regain public confidence in the tobacco industry.

In 1954 the British Medical Journal published the first prospective results from the British Doctors Study set up by Doll, confirming that lung cancer rates were much higher in smokers, and increased with the amount smoked. Doll and Hill reported that smokers also had higher death rates from heart disease, chronic lung disease, and many other conditions and, in 1957, the British and Dutch were the first governments to accept officially that smoking caused lung cancer.

John W. Hill, Hill and Knowlton’s president at the time, said that denying the facts would not be enough as this would clearly be borne from self-interest. Instead, demanding more science was a better tactic. He suggested that the goal of the tobacco industry should be to build and broadcast a major scientific controversy which would convey the message that the health effects of smoking were not conclusively known. One way to achieve this end was to commission more research into the causes of illness. Hill proposed the creation of a research group which would serve a public relations purpose demonstrating the tobacco industry’s collective concern for the public. The Tobacco Industry Research Committee was founded. In an advert published in more than 400 newspapers across the United States, tobacco companies promised to explore the science of tobacco and to ensure consumer well-being.

A wide range of other industries have subsequently adopted similar strategies to invent scientific controversy to undermine public action to address known harms. While the tobacco industries have now conceded and accept that tobacco smoking causes cancer, respiratory and cardiovascular diseases, the fossil fuel industries and their supporters are doing their utmost to undermine acceptance of the evidence and consensus on global warming.

The Guardian recently documented the evidence that the fossil fuel industries’ own scientists were advising them in the 1970s that there was an “overwhelming” consensus that fossil fuels were responsible for atmospheric carbon dioxide increases (8). And a confidential report prepared for Shell found that CO2 could raise temperatures by 1C to 2C over the next 40 years with changes that may be “the greatest in recorded history”.  In 1990 Exxon funded two researchers, Dr Fred Seitz and Dr Fred Singer to dispute the mainstream consensus on climate science. Seitz and Singer were previously paid by the tobacco industry and questioned the hazards of smoking. Singer, who has denied being on the payroll of the tobacco or energy industry, has said his financial relationships do not influence his research (8).