MANAUS, Brazil — Joe Biden witnessed the devastation of drought up close as the first sitting American president to visit the Amazon rainforest Sunday, declaring that nobody can reverse “the clean energy revolution that’s underway in America” even as the incoming Trump administration is poised to scale back efforts to combat climate change.

The massive Amazon region, which is about the size of Australia, stores huge 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.

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

But he’s about to hand the nation over to Republican President-elect Donald Trump, who is highly unlikely to prioritize the Amazon or anything related to climate change, which he’s 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 he says he’ll rescind unspent funds in energy efficiency legislation.

“It’s true, some may seek to deny or delay the clean energy revolution that’s underway 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.”

His trip comes as the U.N. climate conference is underway in Azerbaijan. Brazil will hold the talks next year.

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 — introducing his daughter and granddaughter — 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 U.S. proclamation designating Nov. 17 as International Conservation Day.

The U.S. 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 and 10% of Earth’s biodiversity. About two-thirds of the Amazon lies within Brazil. 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 U.S. was on track to reach $11 billion 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 U.S. and other wealthier nations have yet to fulfill their pledges to help.

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

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

The U.S. has said it has provided $50 million, and the White House announced Sunday an additional $50 million contribution.

Biden’s trip was significant, but “we can’t expect concrete results from this visit,” said Suely Araújo, 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 $10 billion in public and private investment for land restoration and eco-friendly economic projects by 2030 as well as a $37.5 million loan to support the largescale planting of native tree species on degraded grasslands in Brazil.

The Amazon has been suffering under two years of historic drought that have dried up waterways, isolated thousands of river communities and hindered riverine dwellers’ ability to fish. It’s 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 Inácio Lula da Silva took office last year, he signaled a shift in environmental policy from his far-right predecessor, Jair Bolsonaro. Bolsonaro prioritized 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% 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 2,428 square miles, roughly the size of the U.S. state of Delaware. 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 criticized by environmentalists for backing projects that could harm the region.

While Biden is the first sitting president in the Amazon, former President Theodore Roosevelt traveled 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 15,000 miles, and the former president fell ill with malaria and suffered a serious leg infection after a boat accident.

Biden is making the Amazon visit as part of a six-day trip to South America, the first to the continent of his presidency. He traveled 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 was heading to Rio de Janeiro for this year’s Group of 20 leaders summit.