But the prime minister was accused of “paying lip-service” to the climate emergency after unconfirmed reports that his government is planning a cut in fuel duty in the upcoming budget.
At the G7 summit in France on Monday, Mr Johnson will call on world leaders to unite behind ambitious new targets to halt and reverse the loss of habitats and species and to tackle climate change.
The new PM has put the protection of biodiversity at the heart of his message at the Biarritz gathering, in a move seen by some as a bid to encourage Donald Trump to pay attention to the environment without having to confront him over his denial of man-made climate change.
The new funding is designed to help protect habitats and animal and plant species in the Brazilian Amazon, where more than 70,000 blazes have been identified in a matter of weeks in the worst known spate of fires to hit the region.
Mr Johnson has refused to join France’s Emmanuel Macron and Ireland’s Leo Varadkar in threatening to ditch trade deals with far-right Brazilian president Jair Bolsonaro, who is accused of encouraging loggers and ranchers to clear ancient woodlands.
The PM said the fires should not be used as an “excuse” to interfere in free trade, but Labour has accused him of "cosying up" to an administration in Brasilia which has made little secret of its disdain for environmental protection.
Announcing the emergency spending, Mr Johnson said: “In a week where we have all watched horrified as the Amazon rainforest burns before our eyes, we cannot escape the reality of the damage we are inflicting on the natural world.
“The planet faces two immense threats: climate change and biodiversity loss. These are two sides of the same coin – it is impossible to solve one challenge without fixing the other.
“We cannot stop climate change without protecting the natural environment and we can’t restore global nature without tackling climate change.”
Friends of the Earth climate campaigner Aaron Kiely said: "It doesn't add up for the government to commit to global biodiversity and pay the usual lip-service to the climate emergency while cutting fuel duty at home.
“Nothing short of radical changes are needed right now and getting off our oil addiction is long overdue. All the more reason why effectively encouraging more driving - probably to keep a segment of voters happy - shows a fundamental lack of seriousness.
"Funding to protect the Amazon is not to be sniffed at but, better yet, we could listen to the indigenous people who live there and know perfectly well what is needed to prevent a worsening crisis: leave their land alone.
“Climate change is a problem everywhere and cohesive policy that applies at home as well as elsewhere is needed from this government."
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