Fires rage in the Brazilian Amazon rainforest, known affectionately, albeit not exactly accurately, as the lungs of the Earth, and the citizens of the world, including European and United Nations leaders, have been worried.

Are the fires natural? Are they criminal? Are they caused by climate change? And what does the "Trump of the Tropics" have to do with it?

What's happening in the Amazon?

Large expanses of the Amazon were set ablaze mid year and smoke reached urban centres such as Sao Paulo and Belo Horizonte hundreds of kilometres away, alarming residents.

The Amazon rainforest covers 5.5 million square kilometres over several countries: from the middle of Brazil to Colombia, Venezuela, Guyana, Suriname and French Guyana to the north; and Peru, Colombia and Ecuador in the west. The Brazilian Amazon forest accounts for 60 per cent of the total Amazon and spreads over nine states, the larger of which is, confusingly, also called Amazon (Amazonas in Portuguese).

There was not one large bushfire but thousands of fires spread all over the Brazilian Amazon – in particular, along the southern edges of the rainforest where it reaches into Para, Mato Grosso and Rondonia states.

This year through November 5, 77,239 fires were detected in the rainforest, home to 10 per cent of all known plant and animal species. That was up 31 per cent from a year earlier, according to data from the National Institute of Space Research, known as INPE. Still, the pace of new blazes has slowed from a peak in August.

Illegal land clearing is a grim reality in Brazil – graziers, miners and large industrial farming concerns have been clearing land in these states for decades to satisfy demand for soybean crops, cattle grazing and gold and other minerals. Agriculture is the biggest factor in deforestation. But the record number of fires detected by the Brazilian Space Agency INPE in the first seven months of this year, the satellite images and the smoke have brought the issue to the world's attention.

The effects have been felt well beyond the rainforests. Brazil's mega-metropolis Sao Paulo (population 21.5 million, area 7900 square kilometres) went dark in the middle one afternoon in August. It is some 1400 kilometres away from the forest. A frenzy of social media posts, hashtags, accusations and media articles followed, making claim and counter-claim about the cause of the phenomenon.

Hysterics aside, it appears some of the smoke from the Amazon fires did reach Sao Paulo and other areas in the south-east, following the natural path of the Amazonian "flying rivers". It created a smoke cloud corridor seen in satellite images moving south-easterly. Meteorologists, however, are cautious about pointing to the smoke as the only cause for the darkness. They say it was more likely it met a cold front and created the unusual darkness.

According to the European Union's Copernicus Climate Change Service, the fires have led to a clear spike in carbon monoxide emissions as well as planet-warming carbon dioxide emissions, posing a threat to human health and aggravating global warming, The Washington Post reported.

Why is the Amazon so valuable?

By some accounts, the rainforest sequesters some 70 billion tonnes of harmful carbon dioxide, benefiting the entire planet. It stores some of this in the soil, working as a carbon sink. Through photosynthesis, it transforms the rest into oxygen, which is pumped back into the atmosphere.

The rainforest also produces copious amounts of moisture – water vapour that falls again locally as rain but that also travels in what is known as "flying rivers" or atmospheric rivers. These air currents carry Amazon moisture to the rest of Brazil, parts of South America and, according to some scientists, across the Atlantic to parts of Africa and Europe where, in turn, it brings on rain. Former Brazilian environment minister Jose Sarney Filho says this moisture system makes Brazil not the lungs of the world but its air-conditioning.

When the forest burns, it not only stops removing harmful gases from the atmosphere and producing oxygen and rain, it actually produces more carbon dioxide, adding to pollution and greenhouse gases.

Are the fires the result of climate change?

Everything that happens in the Amazon affects and is affected by the planet's climate. Tropical rainforests enjoy two, rather than four, annual seasons – the dry and the wet (some scientists say this used to be "wet and wetter"). It is mostly moist all the time, except for deforested areas, which are now experiencing less rain and, consequently, less water volume in rivers. Some areas have had to curb irrigation, and food production has been affected. But the Amazon is not in drought.

The dry season is, however, the most efficient time of the year to conduct "queimadas" or burns. For thousands of years, indigenous people have used queimadas selectively to grow food without burning down the entire forest. The queimadas, seen from space in modern times, are deliberately lit for land redevelopment – mostly illegally.

From January to July, INPE recorded more than 74,000 burns in Brazil, half in the Amazon, compared with slightly fewer than 40,000 the same period last year – an increase of 83 per cent. This compares to nearly 68,000 blazes in the same period in 2016, when the nation suffered severe drought conditions resulting from a strong El Nino.

INPE's satellite images spotted 9507 new forest fires in the Amazon over five days just last week.

"There is nothing abnormal about the climate this year or the rainfall in the Amazon region, which is just a little below average," INPE chief scientist, fire surveillance, Alberto Setzer told Reuters. "The dry season creates the favourable conditions for the use and spread of fire but starting a fire is the work of humans, either deliberately or by accident."

Danilo de Urzedo, forestry engineer and PhD candidate at the University of Sydney, has spent years studying the Brazilian rainforest and working to reverse deforestation by planting. He says an increase in greenhouse gases helps increase temperatures in deforested areas, in turn heating up the soil, contributing to the spread of fires and the degradation of water quality.

"Tropical forests are also very sensitive to global changes in temperature and to increased greenhouse gases. It's all interconnected," he said.

How did the fires start?

Evidence points to agricultural businesses. Indigenous leaders and activists have been warning about the destruction of the Amazon for decades. In fact, the last time the world was as concerned about the destruction of the Amazon was in 2004 when it hit peak deforestation rates. Concerted efforts from indigenous leaders, activists and environmentalists then saw the government adopt a number of mitigating policies, including the establishment of leading-edge, real-time monitoring systems, some partly funded by European countries.

From 2004 to 2014, Brazil enjoyed a 70 per cent decrease in deforestation, according to Urzedo, as a direct result of the government's environmental policies and the oversight of countries such as Norway and Germany through the Amazon Fund. But from 2014, an economic and political crisis coincided with a rise in deforestation, culminating in the current numbers after the election of right-wing Brazilian President Jair Bolsonaro.

Urzedo says the fires are definitely not a natural phenomenon. He says it reflects the areas cleared for pasture and recent changes in Brazilian environmental politics.

"Fires can start naturally in the areas where the Cerrado joins the tropical forest, but they reflect the areas that have already been cleared to turn forest into pasture," Urzedo said.

"The areas are illegally chosen – first for trees of large economic worth, sold illegally, then the fires open up the land, then comes the conversion from forest to grazing land for farming."

What did Brazil's leader, Bolsonaro, say?

Under pressure from the media and the international community, Bolsonaro first suggested "greenies" started the fires to make him look bad. Asked for proof, he offered none.

The controversial far-right leader, known as the Trump of the Tropics for his antics and disregard for convention, fired the director of Brazil's space agency at the start of the crisis because he distrusted the agency's statistics. He dismissed alarming reports as fake news and INPE's numbers as lies.He called the fires "criminal" but cast doubt on who lit them.

French President Emmanuel Macron on August 23 called the fires an "international crisis". "Our house is burning. Literally. The Amazon rain forest - the lungs which produces 20 per cent of our planet's oxygen - is on fire," Macron tweeted.

Bolsonaro dismissed the comments as "typical colonialism".

Bolsonaro's election promises included opening parts of the Amazon to economic development. He is a declared climate sceptic and has threatened to follow USPresident Donald Trump out of the Paris climate accord.

Since his inauguration in January, many safeguards have been dismantled to satisfy the ruralist faction in Congress. Several environment and indigenous protection agencies and associated institutes have been disbanded, had their resources cut or personnel redistributed, contributing to a lack of focus on policing and an understanding by landowners that it was OK to press on with what they believe to be economic progress.

Bolsonaro even attempted to fold the Environment Ministry into the Agriculture Ministry but reversed the decision after an outcry.

In November, Reuters reported he annulled a 10-year-old regulation that had banned the expansion of sugar-cane planted in the Amazon, in a wetland savanna called Pantanal and in indigenous and reforested areas, according to a resolution published in the country's official gazette. At the same time, fires also were ripping through the biodiverse region, consuming an area the size of London in just 10 days, burning some Pantanal animals alive and sending others fleeing.

What do the indigenous people say?

Davi Kopenawa Yanomami, a shaman and spokesman for the Yanomami people of Brazil, has taken his message of environmental protection to the four corners of the globe. On August 22, from his home in Boa Vista, Roraima, Kopenawa told The Age and The Sydney Morning Herald city people don't listen.

"The Yanomami people have been telling people from the cities that we are worried. We tried to tell them. But the agribusiness and the authorities got together and authorised the deforestation to make grazing land for cattle. People from the city don't believe us. They don't listen," Kopenawa said, alluding to changes of environmental policy by the current government.

Kopenawa feels like the forest is dying.

"The fire is killing the forest and the small regrowth trees. The animals too – tapirs, macaws, peccaries, bees, all the beauty in the universe. They are trying to kill it.

"It's already dying. The people who bought [land in] the forest, the rivers, they are destroying it. That's Bolsonaro's fault. He doesn't speak for the Amazon."

Does this spell doom for the Amazon?

In his 2013 book The Falling Sky - Words of a Yanomami Shaman, Kopenawa predicted an ecological collapse arising from the destruction of his people and the Amazon forest – this he called the time of the "falling sky". Many a social media user referenced this to declare this week's urban darkness a prophecy fulfilled.

Asked about it on August 22, Kopanawa said: "We talked about this. Indigenous people talk, we try to teach, try to make people think, but people don't believe us, they keep knocking down the trees.

"Here from Roraima I too can see the smoke, the yellow air, the yellow ground. Sickness is coming."

Kopenawa said he wanted to see Amazon policies that are sustainable.

Asked if he was tired of repeating the same message over decades he replied:

"I'm not tired. I'll say it once more for city people to understand: What is the forest? The forest is health, for the Brazilian people, for all the people."

In a video published by the German Environment Ministry, the Brazil space agency's Setzer said the future of the Amazon was in politicians' hands.

"The difficulty today is not technical any more, we know precisely what's being deforested, how, where and by whom. What remains to be done is the political will to stop deforestation and forest fires in Brazil."

The German government also hinted at Europe's ability to demand change through trade, or curbs to it, in order to save the Earth from the devastating effects of the destruction of the Amazon.

Brazil's new trade pact with Europe ties the country to the Paris accord under which Brazil is committed to delivering 12 million hectares of reforestation in the Amazon. An increase in deforestation makes it harder for that goal to be met, directly threatening trade.

What's being done about it?

The French President threatened to block a European Union trade deal with the Mercosur bloc of  South American countries, and made sure to put the Amazon fires on the agenda of the G7 in Biarritz in August. Europe offered a $US20 million aid package to help Brazil fight the fires but it was rejected.

Instead Bolsonaro ordered troops and military aircraft to fight the fires but more have been lit since then and tribal leaders have been assassinated for standing up to the forest.

Global leaders, environmental groups and consumers have expressed sharp criticism over Bolsonaro's tactics but he continues to insist development of the Amazon is paramount to the country's economic growth.

Meanwhile, Brazilian agricultural groups have warned that major importers could start snubbing purchases from the commodity powerhouse because of environmental concerns.