Al Gore described it as “in many ways the most serious crime of the post-world war two era, whose consequences are almost unimaginable”. Can you guess which one the former vice-president meant? Genocide in the former Yugoslavia? Genocide in Rwanda? The attack on the twin towers? The oxymoronic “war on terror” that produced – rather than eliminated – terrorism? The nuclear arms race? The invasion of Ukraine? The crimes of Stalin, Mao, or Pol Pot? Or other ones I haven’t the space to cite?

Gore is in fact referring to a very specific moment that occurred on 25 July 1997. That day, the US Senate voted by 95-0 for the Byrd-Hagel Resolution, ruling that the US should not sign a climate treaty that would become known as the Kyoto protocol – despite the Clinton administration’s desire for the US to be a world leader in the fight to cut greenhouse gas emissions. It meant that Clinton would only be allowed to take action when developing countries – particularly India and China – were bound by the same strictures.

The worry, touted by purported experts (many of whom were briefed and funded by US oil companies), was that Kyoto would be a disaster for the US. Imposing strict emission controls on the US – while industrialising nations such as India and China were not similarly constrained – would cost the US upwards of 5,000 jobs, put more than 50 cents on a tank of gas, whack up electricity bills 25% to 50% and put the struggling US economy at a competitive disadvantage in international markets. Or so it was claimed.

Jane McMullen’s excellent and shocking first instalment of a three-part series, Big Oil V The World (BBC Two) reveals another reason for senators Robert Byrd and Chuck Hagel’s resolution. For many years, the big oil lobby had poured scorn on the growing scientific orthodoxy that humanity is hurtling towards a climate catastrophe and that the leading reason is the rise in emissions of greenhouse gases.

What I didn’t know, and this documentary helpfully explains, is that the US’s largest oil company, Exxon, had labs filled with researchers who had produced detailed reports showing the reality of the climate crisis. That research, though, was suppressed.

The bitter irony, clinched by one of the company’s former climate scientists, Ed Garvey, was that Exxon could have been part of the solution rather than the problem. Garvey worked on Exxon’s carbon dioxide research programme from 1978 to 1983, when it was closed because falling gas prices made it seem an expendable luxury.

Garvey also recalls that there were scientists at Exxon developing alternatives to fossil fuels such as solar power and lithium batteries. But their work was shelved. The future of the planet, Garvey suggests, was deemed less important than Exxon’s short-term profit.

Although the Clinton administration in which Gore served had from the outset committed itself to reducing greenhouse gas emissions to their 1990 levels by 2000, and leaders of industrial nations such as the British prime minister, John Major, called for even deeper cuts, the Senate resolution effectively destroyed the president and his vice-president’s hopes of the US leading the world. Instead, the US, through its inaction, helped hasten the climate catastrophe we now live in.

To clinch this rhetorical point, the programme repeatedly cuts from talking heads to scenes more hellish than those imagined by Dante or Milton. Floods in China, a fiery hellscape in California, storms lashing Louisiana and, in one shot, battering an Exxon gas station.

After seeing such images, I wonder how Hagel, who sponsored that 1997 Senate resolution and went on to become defence secretary, sleeps at night. He was among the climate crisis deniers this documentary catches up with to hear them repent. Off-screen, the excellent interviewer asks Hagel if he feels he was misled, given that Exxon, whose execs lobbied him before the Senate vote, was making a concerted effort throughout the 1990s to cast doubt on the reality of the climate emergency and the role of human activity in increasing global temperatures – even though their own scientists were telling them that the science was sound.

“We now know about some of these large oil companies … they lied,” says Hagel. “Yes I was misled. Others were misled. When they had evidence in their own institutions that countered what they were saying publicly – they lied.” If the truth had been told to Hagel and other climate crisis-denying senators, would the situation be different? “Oh absolutely,” says Hagel. “I think it would have changed the average citizen’s appreciation of climate change and mine. It would have put the United States and the world on a different track. It has cost this country and it’s cost the world.”

Last August, the UN secretary general António Guterres said the Intergovernmental Panel on Climate Change (IPCC) working group’s report confirming the link between human activity and rising greenhouse emissions is “a code red for humanity”. That Senate resolution, McMullen’s film argues, contributed to our climate emergency.

No one in this programme explores the hideous political ramifications of this terrible state of affairs, namely that the virus of capitalism (in the form of big oil) undercut democracy through a sustained campaign of disinformation. How easy it proved for corporations to sucker politicians such as Hagel to subvert not just the will of the people but the wellbeing of the planet. If McMullen’s film has a moral, it’s that democracy must be healthy enough to resist commercial lobbying, so that we don’t get fooled again. In 2022, that seems an unlikely scenario.