The fires in the rainforest have finally been extinguished by the arrival of the rainy season, but threats and violence continue unabated against forest defenders. They need international support if the Amazon is to be at the centre of climate action rather than just another distant frontline in the war against nature.

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For that to happen, the world must wake up to the existential threat posed by the destruction of the Amazon, and show solidarity with traditional communities, land rights activists and environmental NGOs in Brazil. All have come under intensifying pressure since ultra-right militarist Jair Bolsonaro became the country’s president at the start of this year. His government has weakened forest protections and encouraged miners, farmers and land grabbers to take advantage.

The Amazon increasingly resembles a battleground. On one side is an ethnically diverse, ecologically rich mix of indigenous people, riverine communities and quilombolas, or hinterland settlements. On the other is a primarily white capitalist elite, eager to exploit the land. In one form or another, this struggle dates back five centuries to the first European colonialists, but it has taken on global significance as the climate consequences become clearer. Civil rights activists describe a climate of terror. In the past three weeks, alone three indigenous leaders have been murdered along with a key witness due to testify in defence of Catholic priest and land activist Amaro Lopes, the successor of murdered nun, Dorothy Stang. Last month, police raided the Health and Happiness Project, a long-running NGO in Alter de Chão, Santarém, and arrested four volunteer firefighters. With the government on their side, land grabbers feel emboldened to invade and burn more forest.

Human rights campaigners say police are taking the side of land grabbers, and want a meeting with the governor of Parå state to seek reassurance laws will be respected, protected forests will be safeguarded and activists will not become targets. That they have to ask these questions shows how dire the situation has become.This is of global concern. At a time of climate emergency, the Amazon is the world’s biggest terrestrial carbon sink. Amid growing evidence of a breakdown of the world’s natural life-support systems, it is home to more species than anywhere outside the oceans. The rainforest is a vitally important part of the water cycle, channelling rain across South America and shaping the trade winds that circulate weather systems. Calls for tree planting and nature-based solutions to the climate crisis will come to nothing without this rainforest.

But international support for the Amazon has been tepid. This was clear last month in Altamira, northern Brazil, at the aptly named Amazon: Centre of the World gathering. In the days before the meeting, rightwing agitators called for farmers, cattle ranchers, police and other “patriots” to mobilise against traditional communities, environmentalists and human rights groups taking part, that they claimed were “eco-socialists” working for international interests against Brazil’s sovereignty and economic development. These messages were enough to spook two foreign organisations – a huge environmental NGO and one of the world’s biggest foundations – who pulled out of the event., rather than risk becoming embroiled in a potentially tense stand-off. Other foreign groups were uncowed. For domestic activists, threats are a fact of life - and they find their own way to deal with them. At the opening session, a group of land grabbers – some wrapped in the Brazilian flag – shoved their way to the front, jostled the speakers and disrupted proceedings. They were pushed back by Kayapo warriors in war paint, while other activists formed a human barrier to enable the speakers to continue. It was symbolic: white farmers attempting to take over; Amazon dwellers defending their space, while prominent international supporters ran scared.

Facebook Twitter Pinterest Brazilian president Jair Bolsonaro: ‘With the government on their side, land grabbers feel emboldened to invade and burn more forest.’ Photograph: Adriano Machado/Reuters

This is a shame on our generation. The Amazon (along with the Congo and Papua New Guinea, the oceans and other capitals of nature) should be as central to global debate and international activism as the Spanish civil war was in the 1930s. Back then, working-class idealists joined public intellectuals in the fight against fascism. George Orwell, Martha Gellhorn, WH Auden, Pablo Neruda, Emma Goldman and Ernest Hemingway were among tens of thousands who risked their lives reporting on the fighting or taking part in it as members of the International Brigade. Some saw it as a civilisation-defining moment. Others described it in apocalyptic terms as “the last great cause”. For Orwell– who was shot in the conflict – it was simply a fight for “common decency”.

Unlike then, the threat to civilisation and decency is not a new ideology, but the accumulated consequences of the old one. Bolsonaro, Donald Trump, Vladimir Putin, Rodrigo Duterte, Recep Tayyip Erdoğan and other populists may often resemble fascists, but actually they are arch-capitalists. Their main appeal to voters comes not from a twisted vision of a future but from a promise to turn back the clock to a more stable age. This is impossible, because manmade climate chaos is increasingly disrupting more lives and economic activity. Until governments deal with that, all other battles will be futile.

That is why defence of the Amazon – and the broader struggle to restore nature – is today’s “last great cause”. Move this issue from the periphery to the centre and everything – global politics, economics and individual thinking – changes. Ecology will be seen as more fundamental than economy, long-term fertility will come ahead of destructive GDP growth, ecocide will be punishable in criminal courts, future generations and other species will be given democratic representation, and school curriculums will teach children how to maintain our home, planet Earth.

That may seem a distant prospect. The forces lined up against such a radical but necessary shift in thinking have more political power and force of arms. The same was true in the Spanish civil war. Then, the antifascists lost the war but, as the great historian Eric Hobsbawm noted, they won the battle for ideas. With so many writers, poets and journalists on their side, the losers got to write the history for a change – and this shaped the debate for the bigger conflict that was to come in the second world war.

Similarly, the battle for the Amazon cannot be won on the ground with guns and bombs, but it can be shaped by opinions, money, consumer choices, street protests and international pressure. It is no longer enough for today’s intellectuals, celebrities and other opinion formers to declare support for the rainforest on social networks. More people need to get out from behind their screens, to feel what nature provides and how it is being lost. That requires putting bodies, reputations and cash on the line, rather than leaving the battle to courageous but outmuscled and outmoneyed traditional communities. International organisations and foreign governments need to step up and help Brazil recognise the value of the rainforest. Restoring nature should be pivotal in all decision-making.

This is not just a question of common decency; it is time to treat the Amazon as a matter of life or death – and not just for those who live there.

• Jonathan Watts is the Guardian’s global environment editor