Fires are ravaging the Amazon rainforest, often referred to as the lungs of the planet, with experts calling the thousands of blazes the worst in a decade.

World leaders have declared the plight of the rainforest, which covers millions of kilometers and is famed for its biodiversity, an international crisis.

What is causing the fires?

During dry season, which runs from July to October, it is not uncommon for fires to spark but 2019 has seen unprecedented numbers, according to data gathered from the Brazilian space agency.

The National Institute for Space Research (Inpe) says its satellite data shows an 85% increase on the same period in 2018. The official figures show more than 75,000 forest fires were recorded in Brazil in the first eight months of the year - the highest number since 2013. That compares with 40,000 in the same period in 2018.

Natural events can cause fires, such as lightening strikes but can also be down farmers and loggers illegally clearing land for grazing and crops.

Activists are claiming that Brazilian President Jair Bolsonaro, a known climate sceptic, is encouraging deforestation through his anti-environmental rhetoric.

But Bolsonaro has fired back, accusing NGOs of starting the fires themselves in an effort to undermine his policies.

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Smoke from the fires was so bad that it caused an hour-long blackout in Sao Paulo, more than 2000 miles away. The clouds can also be seen from space.

The Amazon is the world's largest rainforest and is home to about three million species of plants and animals, and some one million indigenous people, and a fifth of the world’s oxygen and fresh water.

The basin is crucial to regulating global warming with its woodlands absorbing millions of tonnes of carbon emissions every year, mitigating the effects of climate change.

The danger lies in when trees are cut or burned so the stored carbon is released into the atmosphere and the forest's capacity to absorb emissions is reduced.

What do the fires mean for the environment?

Smoke fumes from the fires has reached the Atlantic coast and Sao Paolo, according to The World Meteorological Organization. They added that the blazes have released the equivalent of 228 megatonnes of CO2 so far this year, the highest since 2010.

The fires are also emitting carbon monoxide - a gas released when wood is burned and does not have much access to oxygen.

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What is being done about it?

Emmanuel Macron called the fires an international crisis while Angela Merkel said they were “shocking and threatening” and both insisted emergency talks take place at next week's G7 summit.

In England, supporters of Extinction Rebellion UK, responsible for major climate change protests across British cities, have been gathering outside the Brazilian Embassy in London.

Senior figures in the Labour Party have written to the PM to call on him to “immediately tell President Bolsonaro that his reckless destruction of the Amazon has to stop”.