Surely there can be no deal between the Scottish National Party and the Greens if the exploitation of the Cambo oil field, west of Shetland, is allowed to go ahead?

In May’s Scottish parliamentary elections, the SNP won by far the biggest number of seats, but fell just short of a majority. After the election, Nicola Sturgeon announced that she was entering negotiations with the Scottish Greens, which, on the back of their best-ever results, had eight MSPs.

On 28 August, the result of these negotiations will be put to an extraordinary general meeting of the Scottish Greens, where the party’s members will decide whether or not to accept whatever deal the SNP has negotiated with their party’s leadership. There has been much speculation that the proposed partnership would be similar to that between the New Zealand Greens and Jacinda Arden’s Labour, where the Greens get a minister or two but aren’t bound into a full formal coalition.

In the middle of these discussions, events in the rough oceans west of Shetland transformed those conversations. Or they should have done.

For 20 years, a string of oil companies has been slowly progressing exploration of the Cambo oil field, which they were granted licences to explore in 2001. And finally, this summer, they reached the point of applying to the UK’s Oil and Gas Authority for consent to proceed with extraction.

While the British state is doling out licences to suck combustible fossils from the bed beneath the North Sea every few months, this case is extraordinary. There are around 800 million barrels of oil in the field in question. Burning it all would produce around ten times Scotland’s current annual carbon emissions. For Greens, fiddling around with domestic transport or energy policy while allowing Cambo’s oil to burn is surely unacceptable.

Officially, the power to allow oil company Siccar Point to proceed lies with the UK government – the Oil and Gas Authority sits within the British rather than the Scottish government. But this doesn’t mean that the SNP is powerless.

Most obviously, the party can speak out. Initially, Nicola Sturgeon was reluctant to do even that. When questioned by activists, she hummed and hawed. More cynical Greens speculated that she was holding back her opposition so that she could use it as a card in the ongoing negotiations with their party.

Then, yesterday, she issued a slightly clearer statement. But only slightly: she wrote to Boris Johnson, calling on him to ‘reassess’. But she didn’t make clear that he should stop the oil being burned, and was accused of hiding behind him.

In reality, she could do much more than write firmly worded letters. When the SNP first came to power, it made it clear that it would oppose any new nuclear power stations in Scotland. Officially, energy policy rests with Westminster. But planning policy is devolved. And if Sturgeon announced that she was going to amend the national plan, with a mind to barring all new oil industry infrastructure, she could gum up any new oil exploration.

Two years ago, the SNP government effectively banned fracking in Scotland using planning powers.

It’s not just Cambo. Oil yet to be extracted from the North Sea contains far more carbon than can safely be burned. And in a world where huge numbers of countries are sitting on fossilised wealth sufficient to fry the planet many times over, why on earth should we – who have contributed more of the tonnes of carbon in the atmosphere per capita than almost any other nation on earth – have the right to insist that it is ours that can be burned?

The Scottish Tories, of course, will continue to squeal – today, they’ve continued their audition to be outriders for the horsemen of the apocalypse.

But any viable response to the climate emergency has to mean a rapid transition away from fossil fuels, which means leaving the stuff under the sea. Instead, too many Scottish government policy documents prevaricate on the matter, or, worse, indulge in the ‘magical thinking’ of carbon capture and storage. Those aren’t my words. They come from the leading scientific journal, Nature.

Friends of the Earth Scotland is equally clear. As its climate and energy campaigner, Caroline Rance, put it to me, “To avoid climate breakdown there can be no new developments like Cambo, and existing production must be wound down over the next decade. Every tonne of carbon and every fraction of a degree matters.

“The Scottish government should stop deferring to Boris Johson and say clearly that Cambo must not go ahead. The Scottish government has rightly stopped new nuclear power going ahead, eventually stopped fracking, and frequently speaks out against Westminster policy that it believes to be unjust. If it puts its mind to it, it could make it extremely difficult for new oil and gas infrastructure to be built in Scotland.”

Sturgeon is often reluctant to flex her constitutional muscles. But I was there, in the audience, at the 2015 United Nations Climate Change Conference in Paris, when she spoke of her commitment to prevent the heating of the planet. She sat on a stage with people from Pacific Island states who wept as they told the stories of their countries drowning beneath the waves.

If she meant anything she said that day, if she wants to be able to walk tall at the UN climate conference in Glasgow this winter, then she must use what powers she has to stop the Cambo oil field. She must instead ensure the just transition for oil workers into the jobs of the future that my friends and neighbours who are employed by the North Sea oil industry are desperate for.

And if the Scottish Green members are going to vote for any kind of co-operation agreement with her government, it must include a firm commitment that such a government will use every bit of power it has to drive the rudder of the Scottish economy towards a sustainable future.

Because the alternative is watching the planet burn.