The US-based CIEL recently republished an industry-funded report prepared by the Stanford Research Institute warning that petroleum production could have serious consequences for the planet and humanity, but that for decades the API continued to deny the scientific basis of climate change.

It comes as there is now an overwhelming expert scientific consensus on human-caused global warming.

The authors of seven previous climate consensus studies have published a new paper, co-authoured by University of Queensland’s John Cook, which aims to settle this question once and for all: studies find 97% consensus among publishing climate scientists that humans are driving global warming.

Further, the greater the climate expertise among those surveyed, the higher the consensus on human-caused global warming.

CIEL says that Big Oil knew unequivocally by the early 1970s that significant temperature changes were almost certain to occur by the year 2000, and ignored the warnings.

“If the Earth’s temperature increases significantly, a number of events might be expected to occur including the melting of the Antarctic ice cap, a rise in sea levels, warming of the oceans and an increase in photosynthesis,” the Stanford report warned.

“It is clear that we are unsure as to what our long-lived pollutants are doing to our environment; however, there seems to be no doubt that the potential damage to our environment could be severe.”

The study, written by scientists Elmer Robinson and RC Robbins, added that accumulation of CO2 in the atmosphere could cause “serious worldwide environmental changes”

They estimated that CO2 in the atmosphere could reach 400 parts per million by 2000, however it did not that level until 2015, driving a one degree increase in global temperatures over the past 100 years.

The Robinson Report was presented to the World Petroleum Congress in 1971 and a 1972 industry report authored by a steering committee of high-level executives was submitted to the US Department of Interior on air pollution issues. It relied on Robinson’s report and publicly referred to “their careful study” by “eminent scientists” as an authoritative source on atmospheric pollution, but it appears the API had commissioned a supplemental report that took a more sceptical, more equivocal approach to climate science.

CIEL says API had recognised issues with fossil fuels in the 1940s, setting up the Smoke and Fumes Committee to fund research into emissions and air pollution, largely through Stanford.

It was long suggested that the oceans covering 70% of the planet’s surface would absorb the excess CO2 released by human activity, and mute any impact on the atmosphere, however by 1957 a landmark paper by Roger Revelle and Hans Suess of the Scripps Institute upturned that conventional wisdom, demonstrating that far more CO2 would remain in the atmosphere than previously assumed, potentially accelerating the impact of global climate change.

That led to a paper from Humble Oil (now ExxonMobil) scientists led by HR Brannon that warned ExxonMobil of the risks of climate change – not only rising levels of atmospheric CO2, but also the evident contribution of fossil fuels to that increase – the earliest “indisputable” evidence CIEL has found.

However, the Brannon paper suggests that CO2 would be retained in the oceans much longer before returning to the atmosphere, which would delay by decades or centuries the impact of fossil fuel emissions.

Environmentalists say that three-quarters of the world’s known fossil fuel reserves, will have to remain in the ground if the Earth is to avoid the worst impacts of climate change.

Climate change had not generally been on the international community’s radar until the 1980s, meaning the API knew two decades before the rest of the world, CIEL said.

Last year, it was claimed that ExxonMobil, the world’s largest oil company, knew of climate change as early as 1981, only to spend millions of dollars over the following decades to promote climate denial.

CIEL said hundreds of documents show oil and gas executives met in 1946 to agree that they should fund research into air pollution issues, but the findings were “covered up”.

The group said the documents are the “tip of an evidentiary iceberg” that demands further investigation.

“Oil companies had an early opportunity to acknowledge climate science and climate risks, and to enable consumers to make informed choices. They chose a different path. The public deserves to know why.”

ExxonMobil is already the subject of probes from four attorneys-general in the US, led by New York.