The Supreme Court’s judgment on prorogation arrived at the Labour Party Conference in Brighton like a thunderbolt: MPs’ schedules were immediately rearranged; press officers were jubilant to have something apart from party infighting to brief on; occasional smiles even broke out on the conference floor. But Parliament’s dramatic return produced a clash of mental gears: from attempts at the conference to think seriously about the shape of Britain and the world over the next decade, to fervid calculations in the House of Commons, where the horizon barely extends beyond a dispiriting 24 hours.

Parliamentary short-termism is an enduring affliction, even in sedate times. This week’s nadir came with the prime minister’s wholesale importing of the language of the alt-right into his performance at the despatch box: over and again he spoke of the ‘Surrender Act’ passed before prorogation; his attorney general, in the warm-up slot, bellowed that this ‘dead Parliament’ had forfeited its ‘moral right’ to sit. When reminded that the language of ‘surrender’ and ‘treachery’ was associated with the murder of Jo Cox, Johnson gave little more than a sneer. It was hard to watch the malevolent pantomime without thinking of the earnest anxiety of some of the Labour Conference debates, or the distraught and unvarnished message delivered by Greta Thunberg to the UN two days earlier: ‘You are failing us.’

On Tuesday, Labour delegates voted in favour of a Green New Deal. It commits the party ‘to aim for net-zero carbon emissions by 2030, nationalisation of the big six energy companies, the guarantee of new good unionised jobs as part of a worker-led just transition, free or affordable integrated green public transport, and support for the Global South and climate refugees’. It is the most serious programme on climate change adopted by a major political party anywhere on the planet.

The GND’s troubled passage from campaign to party policy, however, points to a few of the problems it may now encounter. The negotiation process among various party actors (trade unions, the leadership, members), designed to come up with a single composite motion to present to the floor, broke down over the inclusion of a 2030 target. Trade unionists have been sceptical about target dates, arguing not only that are they usually not met, but that they become an excuse to smash workers in carbon-intensive industries; campaigners contend that without a date the policy is fundamentally unserious, and fails to grasp the urgency of the climate crisis. In the end, two motions – one with a date, one without – were passed by conference. It remains to be seen what form the policy will take in a general election manifesto.

Critical histories of the Labour Party note that the trade unions have often acted as a brake on the left’s more ambitious projects, distrusting policy that doesn’t include concrete protection for their workers. They note, too, that conference’s nominal sovereignty is in practice sapped by the near total autonomy of the parliamentary party, and the veto powers available in the manifesto-writing process: Labour activists have not forgotten the ease with which Blair ignored conference resolutions. Yet what is most startling about the Green New Deal’s passage is not the division, but the strength of trade union support for both motions – including impassioned speeches from prominent trade unionists on green technology and climate reparations. This is a sign of a profound shift in the trade union movement, difficult to imagine just a decade ago.

Campaigners on all the major policy initiatives are right to fear their dilution in the manifesto: this is especially true of the measures on private education and free movement. The Green New Deal has been more warmly embraced by the leadership, and its urgency makes it harder to water down. Still, climate activists face a major political crux: it is impossible to tackle climate change without taking state power and using the state’s unrivalled resources to restructure society towards carbon neutrality, but the vehicles for doing so – political parties – are complex and often fraught coalitions, in which fears have to be allayed and livelihoods protected, and democratic consent sought for sweeping change. GND campaigners hope the popularity of the idea within and beyond the Labour Party’s ranks will compel the leadership to take it seriously, not least because of its sheer moral weight.

That weight is especially clear in the speeches that Greta Thunberg gave recently in New York, to climate strikers last Friday and to the UN Climate Action Summit on Monday. Thunberg has been compared to an ancient Greek parrhesiastes, one who fearlessly speaks an unwelcome truth, at risk to themselves, and in so doing reshapes politics; she also bears resemblance to Brecht’s Antigone. In a poem written for the premiere of his version of the tragedy, written immediately postwar but set in 1945, Brecht implores Antigone to ‘come out of the shadows’: ‘You let the powerful off/Nothing and with those confusing the issue/You did no deals.’

Thunberg’s powerful and unyielding speeches galvanise climate protesters, and drive her opponents to scabrous and slanderous fury: they look for the ‘real’ reason behind her politics – attributing it to personal privilege, or indoctrination – or make poisonous claims about her mental health. Nominally progressive political leaders, meanwhile, queue up to pay homage in front of the cameras, returning to their electorates with their reputations burnished but their quiescent climate programmes altered only cosmetically, if at all.

Climate change activism generates two contradictory political forces. One is an increasingly urgent popular sense of the scale of the emergency, the devastation that climate change has already wrought and the worse that is yet to come: it energises popular protest and can inspire almost supernatural commitment. The counter-force is not only Koch-funded climate denialism or oil-industry greenwashing, but the deep imbrication of politics with powerful economic interests that have a large stake – however suicidally short-term – in maintaining something resembling the status quo. The CBI response to Labour’s Green New Deal – that there is ‘no credible pathway’ to net-zero emissions by 2030 – is leaden with spurious ‘realism’. Hope, such as it is, comes from the prospect that the first force can either wrench politicians from their cosiness with the second, or replace them.

Extinction Rebellion’s first demand is for governments to ‘tell the truth by declaring a climate and ecological emergency’. In the US, fogged with outright lies and denialism, telling the truth might be a good first step; elsewhere, the truth is widely, if only partially, accepted and understood. In the UK, Parliament has declared a ‘climate emergency’, but the government is still committed to fracking and the continued extraction of North Sea hydrocarbon reserves. The truth in itself is insufficient for action: only in concert with political organisation and planning can it make a dent.