International pressure may be the only way to stop the Brazilian government from taking a “suicide” path in the Amazon, one of the country’s most respected scientists has said, as the world’s biggest rainforest continues to be ravaged by thousands of deliberate fires.

The large number of conflagrations – set illegally to clear and prepare land for crops, cattle and property speculation – has prompted the state of Amazonas to declare an emergency, created giant smoke clouds that have drifted hundreds of miles, and sparked international concerns about the destruction of an essential carbon sink.

“Our house is burning,” tweeted the French president, Emmanuel Macron, who called for emergency talks on the subject at this week’s G7 summit. But the response to the crisis has been mixed: while Norway and Germany have halted donations to the Brazilian government’s Amazon fund, the EU has recently signed a trade deal with South America, and the UK spent this week focusing on post-Brexit business with Brazil.

On Wednesday, the UK trade minister Conor Burns was shaking hands with his counterparts in Brasilia and declaring a desire to “deepen relations”. Asked about the fires, he declined to comment but reportedly said Bolsonaro’s government had “legitimate ambitions to bring prosperity to its people”.

Scientists say the ongoing destruction will have dire consequences for Brazil and the world.

Carlos Nobre, a senior researcher with the Institute of Advanced Studies at the University of São Paulo, said the surge in deforestation was taking the rainforest closer to a tipping point beyond which swaths of the usually humid forest would become a dry savannah, with dire consequences for the climate, wildlife and forest dwellers.

Nobre said deforestation was on course to rise by 20-30% this year and was “very likely” to pass 10,000 sq km for the first time in more than 10 years. The trend has been worsening for several years, but it has accelerated under Bolsonaro, who has weakened the environment agency and expressed support for miners, farmers and loggers.

“The situation is very bad. It will be terrible,” Nobre told the Guardian. “A very large number of these fires are due to the cultural push that ministers are giving. They are pushing deforestation because it is good for the economy. Those who do illegal deforestation are feeling empowered.”

Nobre co-authored a study last year that predicted the southern, eastern and central regions of the Amazon would reach an irreversible stage of degradation once 20%-25% of the forest was cleared. This was not expected for 20-25 years, but Nobre said the tipping point was likely to be brought forward by about five years if this year’s rate of forest destruction continued.

In the five days to Wednesday, there were 7,746 fires in Brazil, according to data from the country’s National Institute for Space Research (INPE). This follows a 278% rise in deforestation last month. The figures are preliminary, but a rising trend has been observed by other satellite monitoring systems.

Brazil has recorded more than 72,000 fires this year, an 84% increase on the same period in 2018, according to the INPE. Not all were forest fires, but more than half were in the Amazon.

In one of the worst affected municipalities, Porto Velho, environmental activists said there were fires around the city and the streets were filled with smoke.

“People are scared. The hospitals are full of people with respiratory diseases. In 60 years, this is the first time I feel difficulty breathing,” said Ivaneide Bandeira Cardozo, the coordinator of the environmental organisation Kanindé. “It’s a thousand times worse than in other years.

“Bad farmers think they can commit all kinds of illegality because they will suffer no punishment … It seems Brazil has no law, that all the laws are in tatters.”

In the soya frontier state of Mato Grosso, which has had more fires than anywhere else in Brazil this year, burning has been detected inside indigenous lands and nature reserves.

The vast majority of Brazilians want to protect the forest, according to opinion polls, but the government has prioritised business interests. Bolsonaro announced this week that he would resume mega-hydro projects in the Amazon that were halted on environmental grounds. His son has proposed a bill in Congress that would further weaken protections around indigenous territory and nature reserves.

Nobre said one of the few remaining ways to prevent a dangerous loss of forest was through external protests and consumer actions.

“Politicians in Brazil pay more attention to international pressure than the voice of Brazilians,” he said. “I think international pressure is essential to reverse this tragic pathway. The agriculture sector in Brazil is very concerned that European consumers won’t buy Brazil produce. This may be the ultimate way to stop the Brazilian government from a suicide of the Amazon, which will have terrible consequences for the climate and for Brazil.”

These concerns were echoed by Thomas Lovejoy, a co-author of the tipping point study. In more than 50 years working in the Brazilian rainforest, he said this was one of its darkest moments, he said.

“There have always been some ups and downs, but the overall trajectory has been towards improvement. Now, Brazil is headed in the other direction.

“Under normal circumstances, the outside world would endeavour to help, but this Brazilian government is not interested in help.”

The scientists said there were already signs the tipping point was drawing closer. The dry season in the southern and eastern Amazon was more than 20 days longer than it was 30 years ago, droughts were more common, and plants that relied on high humidity were declining. In deforested areas, these trends were more pronounced.

Nobre said: “If the dry season extends two to three weeks more we will reach a critical moment. If it lasts longer than four months, this is the climate envelope of a savannah.”

Global heating is a major factor. As in Siberia, Alaska and California, climate breakdown is expected to make fires more frequent and more widely spread. Some of the biggest fires this week have been in the Bolivian Amazon, where deforestation has also been accelerating. According to Europe’s Copernicus satellite monitoring agency, this was the origin of the smoke that darkened the sky in São Paulo, thousands of miles away, on Monday.

There have been more large fires in Colombia and eastern Brazil this week than in the Amazon, where many agricultural burn-offs are in deforested areas.

In the Brazilian Amazon, only Amazonas state has registered a record for fires so far in August. Globally, huge fires in the Arctic have been even further from the norm, but Brazil remains the centre of concern because the problem is more immediately manmade.

Bolsonaro has tried to deflect blame. He sacked the head of the space agency and said the satellite data was a lie. His chief of staff claimed European environmental concerns were a plot to constrain Brazil’s economic growth. His foreign minister tweeted that it was a tactic by the international left. This week, he suggested, entirely without evidence, that environmental groups might have started the fires to embarrass his government.

This last allegation was condemned on Thursday in a letter signed by 118 civil society organisations. “The president doesn’t need NGOs to burn the image of Brazil in the world,” they wrote.

Concerns about the deteriorating situation have prompted protests at Brazil’s embassies. The UN secretary general, António Guterres, has also urged Brazil to take action. “In the midst of the global climate crisis, we cannot afford more damage to a major source of oxygen and biodiversity. The Amazon must be protected,” he tweeted.

Macron said he would put the matter on the agenda of the G7 summit in France this weekend, while celebrities including Leonardo DiCaprio, Madonna and Cristiano Ronaldo have also raised the alarm.

In Brazil, a petition by the campaign group Avaaz asking the government to halt illegal deforestation has received 1.1m signatures. Federal prosecutors in Pará state are investigating why environmental inspections have declined and military police are absent from inspection operations, where they used to provide protection.

Some foreign governments and conservation groups are trying to deal directly with Brazilian state governments and NGOs rather than going through the national authorities.

The UK, however, has been more focused on building post-Brexit business relations. Brazil’s international trade minister, Marcos Troyjo, said that along with ongoing negotiations with the US, Burns’s visit was a sign that Brazil continued to have the trust of the outside world.

“I think there can be no more concrete proof that not only is Brazil open for business but the international community is willing to do business with Brazil,” he said.

The UK’s stance was condemned by Friends of the Earth. The campaigner Guy Shrubsole said: “If this is what we are prepared to do to line up trade deals, rather than take a world-stage opportunity to protect the obviously irreplaceable Amazon, you have to wonder where our priorities lie. The UK government shouldn’t trade with any countries who are ignoring their Paris climate change commitments, least of all Bolsonaro’s Brazil when they’re burning their forests down to sell us and the world soya and beef.”