When Greta Thunberg began her school strike outside the Swedish parliament in 2018, she was alone. Within months, thousands and then millions followed her example.

Some of the most enthusiastic school strikers have been in Belgium, inadvertently launching a national movement that bridges the country’s entrenched linguistic divide.

In the first few months of this year, Belgian teenagers organised 20 weeks of school strikes, events that led to the resignation of a regional environment minister, who had made false claims that the strikes were directed by foreign powers.

Last month, two of the young women who led the Belgian school strikes embarked on a transatlantic voyage to South America with the initial goal of reaching the UN climate conference in Chile. But events did not go to plan.

Four weeks into the journey, 36 climate activists from across Europe sailing on the Regina Maris schooner had reached Cape Verde, the island nation off the coast of west Africa, when they heard of Chile’s abrupt decision to cancel hosting the meeting.

Anuna De Wever said the environment minister taking a private jet to a climate summit spurred her to act. Photograph: Jennifer Rankin/The Guardian

“It’s heartbreaking news,” wrote Anuna De Wever, one of the founders of the Flanders school strikes, who also voiced “full support to the people power in Chile”.

She and Adélaïde Charlier, the Francophone voice of Belgium’s school strikes, both aged 18, are the two youngest on board the Regina Maris, which aims to cross the Atlantic by wind power alone. They had hoped to be at the UN meeting “to hold our politicians responsible for their lack of ambition”, De Wever said.

With no certainty on where the UN meeting would take place, the group decided to go to South America regardless. The Belgian women wanted to keep a promise to meet South American activists who are working to protect the Amazon. A spokesman for the group said its main aim was unchanged: “Putting the climate impact of aviation on the international agenda.”

The day after they left Cape Verde, organisers announced the UN meeting would take place in Madrid.

This means the young crew will be on the wrong side of the world just as the meeting is getting under way. Thunberg hopes to get a lift to Madrid, but those on the Regina Maris acknowledge they cannot make it in time. Instead, the activists are rethinking how they will get their message to global leaders in Madrid, as well as putting pressure on domestic politicians.

Belgium was the second country to undergo the industrial revolution, but its complicated, decentralised politics are hampering efforts to tackle the legacy of coal and steel.

The nation of 11.4 million people and six parliaments is on track to miss climate targets in 2020 and 2030, according to the latest progress report from the European commission.

Belgium has some of the worst traffic jams in Europe, energy-profligate buildings and a saturated railway network.

Adélaïde Charlier is sailing to South America, where she had planned to attend a climate meeting in Chile. Photograph: Jennifer Rankin/The Guardian

The last straw for Belgian young people came when the environment minister, Marie-Christine Marghem, took a private jet to the 2018 UN climate summit in Katowice, while Belgium declined to join “the high ambition coalition” – a group of countries pledging extra efforts to tackle the climate emergency. The text was signed by Belgium’s neighbours, including France, Germany, the Netherlands, Luxembourg and the UK.

“No, it was not a joke, it was true,” recalled De Wever of Marghem’s flight, in a book about the Flemish school strike movement that she launched with fellow activist Kyra Gantois. “It was at that point, sitting at the kitchen table, that we looked each other in the eye and said: enough is enough.”

Launched by the two young women in Flanders, the strikes soon spread to Francophone regions, making them a rare national movement in a country where the linguistic faultline cuts through political parties, newspapers and television stations.

“It is Flemish and French,” De Wever said. “Sometimes there are some arguments, especially in politics, but we don’t care about that and we want to unite everyone to fight with us.”

Leading the movement must have heaped pressure on the young activists. At a recent climate march, Charlier was surrounded by enthusiastic participants asking her to sign their reusable water bottles. De Wever has experienced the ugly side of being in the public eye: she and her friends complained to the police after her tent was ransacked and they were pelted with urine-filled bottles at a music festival this summer.

“It’s a lot sometimes,” she said, sounding buoyant after thousands turned out to the Brussels gathering of the September global climate strike. “You get the good and the bad, but at the end of the day, it is all worth it because it is amazing to see so many people coming on the streets, and you get this result,” De Wever said.

One of the school strikers’ champions is the Belgian climate scientist Jean-Pascal van Ypersele, a former vice-chair of the Intergovernmental Panel on Climate Change. He helped the young activists draft a manifesto and said they had succeeded in putting the climate emergency on the agenda. “[The results] are not a full success, but they are not done, their determination to continue is clear,” he said.

For now, the school strikers are battling Belgium’s highly decentralised political system. Dave Sinardet, a political science professor at Free University of Brussels, said: “The federal level is not competent to overrule the regions if they would not reach certain targets.

“So instead of having a dynamic where the different regions push each other upwards, they rather have a dynamic where they push each other downwards: everybody is looking at the other one saying, ‘you should do more’, so that’s clearly a problem.”

The political scientist argued the school strikes did not lead to expected gains for climate-action parties at the 2019 elections. While Greens made gains in French-speaking Wallonia and the federal parliament, these were “not as good as expected”, Sinardet said, while in Flanders, “you don’t see much climate ambition”.

It remains unclear whether Belgium can find a more decisive response to the climate emergency, following election results that left the country more divided than ever. Flanders moved right with gains for the centre-right Flemish nationalists and the far right, while Wallonia swung left, with victory for the Socialists.

More than 170 days after the elections in late May, Belgium remains without a federal government, although the country has signed up to an EU plan for net-zero emissions by 2050.

For Van Ypersele, a professor at the Université catholique de Louvain, the 2050 target is inadequate. The climate scientist is calling on the EU to reduce emissions to net zero by 2040 to keep global heating below 1.5C, the threshold for avoiding catastrophic climate change.

“We are heading on a train which is moving at a 100km an hour towards a wall … If we only hit the wall when we are travelling at 20km an hour, everyone understands that the damage to the passengers on the train will be infinitely smaller than if we hit the wall at 80km or 60km an hour,” he said.

“It would be better to get to net zero tomorrow morning [ie in] 2040 rather than 2050. It would already be so much better [to get to] 2050 than never.”