United States President Joe Biden has witnessed the devastation of drought up close as he became the first sitting US president to visit the Amazon rainforest, declaring that nobody can reverse “the clean energy revolution that’s under way in America”.

His comments come even as the incoming administration of President-elect Donald Trump is poised to scale back efforts to combat climate change.

The huge Amazon region, which is about the size of Australia, stores massive amounts of the world’s carbon dioxide, a greenhouse gas driving climate change. But development is rapidly depleting the world’s largest tropical rainforest, and rivers are drying up.

On Sunday, Biden said the fight against climate change has been a defining cause of his presidency. He has pushed for cleaner air, water and energy, including legislation that marked the most substantial federal investment in history to fight global warming.

But he is about to hand the nation over to Republican Trump, who is highly unlikely to prioritise the Amazon or anything related to climate change, which he has cast as a “hoax”.

Trump has pledged to again pull out of the Paris Agreement, a global pact forged to avert the threat of catastrophic climate change, and said he would rescind unspent funds in energy efficiency legislation.

“It’s true, some may seek to deny or delay the clean energy revolution that’s under way in America,” Biden said from a podium set up on a sandy forest bed, flanked by huge tropical ferns. “But nobody, nobody can reverse it, nobody – not when so many people, regardless of party or politics, are enjoying its benefits.”

The question now, he said, is, “Which government will stand in the way and which will seize the enormous opportunity?”

‘Heart and soul of the world’

Biden’s trip comes as the United Nations climate conference is under way in Azerbaijan. Brazil, which is hosting the conference next year, holds about two-thirds of the Amazon’s territory.

During a helicopter tour, Biden saw severe erosion, ships grounded in one of the Amazon River’s main tributaries, and fire damage. He also passed over a wildlife refuge for endangered species of monkeys and birds and the expansive waters where the Negro River tributary flows into the Amazon.

He was joined by Carlos Nobre, a Nobel Prize-winning scientist and expert on how climate change is harming the Amazon.

Biden met Indigenous leaders and visited a museum at the gateway to the Amazon where Indigenous women shook maracas as part of a welcoming ceremony. He then signed a US proclamation designating November 17 as International Conservation Day.

The US president leaned into the symbolism of his trip, saying the Amazon might be the “lungs of the world”, but “in my view, our forest and national wonders are the heart and soul of the world. They unite us. They inspire us to make us proud of our countries and our heritage”.

The Amazon is home to Indigenous communities as well as 10 percent of Earth’s biodiversity. Scientists say its devastation poses a catastrophic threat to the planet.

During brief remarks from the forest, Biden sought to highlight his commitment to the preservation of the region. He said the US was on track to reach $11bn in spending on international climate financing in 2024, a sixfold increase from when he started his term.

Poorer nations struggling with rising seas and other effects of climate change say the US and other wealthier nations have yet to fulfil their pledges to help.

“The fight to protect our planet is literally a fight for humanity,” Biden said.

Biden’s administration announced plans last year for a $500m contribution to the Amazon Fund, the most significant international cooperation effort to preserve the rainforest, primarily financed by Norway.

The US has said it has already provided $50m as part of that commitment, and the White House announced an additional $50m on Sunday.

New efforts

Biden’s trip was significant, but “we can’t expect concrete results from this visit,” said Suely Araújo, the former head of the Brazilian environmental protection agency and public policy coordinator with the nonprofit Climate Observatory.

She doubts that a “single penny” will go to the Amazon Fund once Trump is in the White House.

The Biden administration touted a series of new efforts aimed at bolstering the Amazon and stemming the impact of climate change.

That includes the launch of a finance coalition looking to spur at least $10bn in public and private investment for land restoration and eco-friendly economic projects by 2030 as well as a $37.5m loan to support the large-scale planting of native tree species on degraded grasslands in Brazil.

The Amazon has been suffering under two years of historic drought that has dried up waterways, isolated thousands of river communities and hindered riverine dwellers’ ability to fish. It has also made way for wildfires that have burned an area larger than Switzerland and choked cities near and far with smoke.

When Brazilian President Luiz Inacio Lula da Silva took office last year, he signalled a shift in environmental policy from his far-right predecessor, Jair Bolsonaro. Bolsonaro prioritised agribusiness expansion over forest protection and weakened environmental agencies, prompting deforestation to surge to a 15-year high.

Lula has pledged “zero deforestation” by 2030, though his term runs through 2026. Forest loss in Brazil’s Amazon dropped by 30.6 percent in the 12 months through July from a year earlier, bringing deforestation to its lowest level in nine years, official data released last week said.

In that 12-month span, the Amazon lost 6,288 square kilometres (2,428 square miles). But that data fails to capture the surge of destruction this year, which will only be included in next year’s reading.

Despite the success in curbing Amazon deforestation, Lula’s government has been criticised by environmentalists for backing projects that could harm the region, such as paving a highway that cuts from an old-growth area and could encourage logging, oil drilling near the mouth of the Amazon River and building a railway to transport soy to Amazonian ports.

While Biden is the first sitting president to visit the Amazon, former President Theodore Roosevelt travelled to the region with the help of the American Museum of Natural History following his 1912 loss to Woodrow Wilson. Roosevelt, joined by his son and naturalists, traversed roughly 24,140km (15,000 miles). The former president fell ill with malaria and suffered a serious leg infection after a boat accident.

Biden is making the Amazon visit part of a six-day trip to South America, the first to the continent of his presidency. He travelled from Lima, Peru, where he took part in the annual Asia-Pacific Economic Cooperation summit and met with Chinese President Xi Jinping.

After his stop in Manaus, he is heading to Rio de Janeiro for this year’s Group of 20 (G20) leaders summit.