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 apart 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.”