Injustice is easy to oppose after it has receded into the past, and there is no cost to imagining yourself as a hero long after the event. Everyone celebrates the suffragettes now, but at the time they were vilified as hateful spinsters and terrorists. McCarthyism is a pejorative political label on right and left alike now, but at his peak, more Americans approved of Senator Joseph McCarthy than frowned on his witch-hunt. Most people would like to believe they’d have stood up against the homophobia of 1980s Britain – yet, by 1987, only 11% of the British public believed same-sex relations to be “not wrong at all”. Which takes us to climate activism. This year has seen a global onslaught against people agitating for more action to mitigate the worst effects of the climate crisis. Courts can issue stern judgments, but so can history, and you have to wonder its future verdict on how the persecution and silencing of those raising the alarm only escalated when the scientific evidence had become so cast-iron, and when extreme weather events hammered home the imminent danger facing the human species. Here in Britain, a government which is reneging on its climate commitments – not least by expanding oil and gas licences – is simultaneously introducing repressive legislation to silence those holding them to account. After punitive sentences were handed down to climate activists, the UN’s rapporteur for climate change and human rights suggested in November that the sentences potentially breached international law. Indeed, earlier this month, the 57-year old climate activist Stephen Gingell was sentenced to six months in prison. His crime? Participating in a peaceful slow march in protest against new oil and gas licences – something that is now prohibited by the Public Order Act 2023. In the space of a month, at least 470 peaceful protesters were arrested with the aid of the raft of authoritarian measures driven through by Tory rule. Like the climate emergency itself, the persecution of those fighting it is a global phenomenon. At the recent Cop28 summit in Dubai, protesters suffered restrictions on what they and their signs could say and where they could walk. The French government outlawed the climate activist group Earth Uprising under the dubious pretext that it fomented violence; this was rightly labelled by human rights activists as appearing “wholly disproportionate in violation of France’s obligations under international law”. In Australia, new laws imposed steeper prison sentences and fines against climate protesters: all this, as Human Rights Watch notes, as the country faces “an onslaught of record-breaking temperatures, floods, and bushfires in recent years”. In New South Wales, meanwhile, punitive laws to crack down on climate protesters were last week ruled to be unconstitutional because they undermined “freedom of political communication”. Meanwhile, climate activists suffer coordinated attempts to portray them as dangerous extremists. Take the Atlas Network, an influential global grouping of rightwing thinktanks: it has helped lead campaigns across the world to demonise climate activists as dangerous extremists. A report by the climate platform DeSmog argues that this has had real consequences: from the portrayal of the German climate movement Last Generation as de facto terrorists, which helped lay the foundation for police raids against its activists, to the British thinktank Policy Exchange, which is reportedly part of Atlas, publishing a report denouncing Extinction Rebellion as an “extremist organisation seeking the breakdown of liberal democracy and the rule of law”. Rishi Sunak later said that Policy Exchange’s work had helped the government in drafting its legislation to crack down on such protesters. Again, what will our descendants think, not least as they inhabit a world battered by the consequences of today’s failures to address an existential emergency, knowing we were in full possession of the facts? Two months ago, an international team of scientists warned the Earth’s vital signs were in a worse state than in any time in human history, imperilling the future of life itself. From extreme weather events to drought, famine to forced population movements, a bleak future beckons unless the warnings of embattled climate activists are heeded. What is happening is hardly subtle. There is a calculated attempt to claim that the real extremists are not those who imperil our world’s future by fighting policies that would limit carbon emissions, but those seeking to prevent impending calamity. The truth is these climate activists are being targeted not because they are protesting in the wrong way or because their methods are counterproductive, but because they have secured such a considerable platform to make the climate emergency a more salient and discussed issue. Understandably, vested interests profiteering at the expense of the planet have every motive to shut them up. There are politicians with loud voices who acknowledge that the climate emergency is indeed real, but either say nothing when these climate activists face coordinated campaigns to silence them, or even render themselves complicit. In hindsight, it seems so obvious to accept the righteousness of those who fought for the rights of women to vote, or who stood against McCarthyite intimidation, or who fought for gay rights. But these were often lonely battles, and those vindicated by history paid heavy costs at the time. If the climate activists warning of the gravest threat humanity has yet faced are silenced into 2024, we all may find ourselves paying an intolerable price. Owen Jones is a Guardian columnist