MANAUS, Brazi>> President Joe Biden pledged new financial help to protect the Amazon, the planet’s largest tropical rainforest, during a visit to Brazil on Sunday, making one final push to combat climate change before President-elect Donald Trump returns to power in January.

After an aerial tour of one of the world’s most diverse ecosystems, Biden signed a proclamation declaring every Nov. 17 to be International Conservation Day and vowed that the United States would spend millions of dollars across the Amazon on restoring land, planting native tree species, supporting biodiversity efforts and increasing fertilizer efficiency programs. It was the first time a sitting U.S. president had visited the Amazon.

“It’s often said that the Amazon is the lungs of the world,” Biden said during a brief stop in Manaus, a bustling city of 2 million nestled in the heart of the rainforest. “But in my view, our forest and national wonders are the heart and soul of the world,” he added. “The Amazon rainforest was built up over 15 million years. Fifteen million years history is literally watching us now.”

Flying low in his Marine One helicopter across the vast canopy of trees, Biden traveled along the Rio Negro, where its dark waters met the murky brown of the main Amazon River. From his helicopter, Biden could see a wildlife refuge, shore erosion, fire damage and grounded ships, according to a map of the area provided by the White House.

But his initiatives may be short-lived. Environmental activists are bracing for a drastic shake-up in U.S. foreign policy under Trump, who has loudly opposed international cooperation on climate change. He has vowed to abandon global commitments and undo many of Biden’s environmental pledges.

Trump has said he will withdraw the United States — for a second time — from the landmark Paris Agreement, which aims to curb planet-warming emissions and rein in rising temperatures. He has promised to “drill, drill, drill” for oil and gas and nominated Chris Wright, a fossil fuels executive who has claimed “there is no climate crisis,” to lead the Department of Energy.

Top White House environmental officials said Sunday that some of the federal financing to protect the Amazon would go forward before Trump takes office, but not all of it.

In his remarks, Biden acknowledged the threat from Trump without using his name directly. But he expressed confidence that even his successor would not be able to stop efforts to protect the climate that also promote jobs and help make life better for people around the world.

“It’s true that some may seek to deny or delay the clean energy revolution that’s underway in America,” Biden said. “But nobody — nobody — can reverse. Nobody.”

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

A U.S. rejection of the global climate agenda would come at a crucial time in the struggle to contain rising temperatures. Research shows that Earth has already warmed significantly, with the past decade being the hottest on record.

Biden has urged wealthy countries responsible for the bulk of the world’s emissions to help fund programs in poorer countries, where the effects of climate changes are often at their most severe.

In 2021, the United States was among more than 140 countries that vowed to end deforestation by 2030. Last year, Biden also pledged $500 million over five years to fight deforestation in Brazil, although the plan has met resistance from Congress and, so far, the South American nation has received only about 10% of the funding.

“The president has spoken frequently about the importance of U.S. leadership in protecting the Amazon and other tropical forests,” said Nigel Purvis, CEO of Climate Advisers, a consulting firm.

The Amazon rainforest plays a crucial role in regulating the planet’s climate. Likened by scientists to a “giant air conditioner,” the Amazon lowers temperatures, generates rainfall and stores vast quantities of planet-warming gasses.

After Biden landed in Manaus on Sunday, he came off the plane under scorching midday sun, looking relaxed and upbeat. He was accompanied by his daughter, granddaughter and aides, and lingered on the tarmac before boarding one of seven helicopters waiting to take him on the aerial tour.

Biden took in the vastness of the rainforest, and the impact of climate change, at the Museum of the Amazon, an exhibition space and botanical garden in Manaus. He was greeted by three Indigenous women in traditional headdresses who chanted and shook rattles to the beat of an ancestral song. Overhead, macaws swept over the canopy, their noisy squawks echoing across the rainforest.

In recent decades, swaths of the Amazon have been razed and burned to make way for cattle ranches and soy farms. This both releases carbon and reduces the rainforest’s ability to capture it, dealing a double blow to efforts to rein in emissions.

As the destruction has advanced, parts of the rainforest have begun emitting more carbon that they store. And a glimpse into a future of recurrent droughts has rattled countries in the Amazon basin, parching stretches of the world’s largest river, triggering electricity shortages and stranding Indigenous villages.

A growing body of research warns that, if left unchecked, deforestation could push the Amazon to a tipping point that would transform it from a lush rainforest into a grassland savanna.

President Luiz Inácio Lula da Silva of Brazil has also been vocal about the need for wealthier countries to pitch in funds to help preserve the Amazon rainforest, about two-thirds of which lies within Brazil. He has been open about his anxieties about a U.S. pullback from the climate agenda, urging Trump during an interview with CNN this month to “think like an inhabitant of planet Earth” when shaping his climate policies.

From Manaus, Biden is headed to Rio de Janeiro, where he will join a summit of leaders of the Group of 20 nations.

There, Biden’s allies will probably use the president’s last tour abroad to lock in partnerships on climate and other common goals — even if only as symbolic gestures that may be wiped out once Trump returns to power.