In early 2015, scientists monitoring satellite images at Global Forest Watch raised the alarm about the destruction of rain forests in Indonesia.

Environmental groups raced to the scene in West Kalimantan province, on the island of Borneo, to find a charred wasteland: smoldering fires, orangutans driven from their nests, and signs of an extensive release of carbon dioxide into the atmosphere.

“There was pretty much no forest left,” said Karmele Llano Sánchez, director of the nonprofit International Animal Rescue’s orangutan rescue group, which set out to save the endangered primates. “All the forest had burned.”

Fingers pointed to the Rajawali Group, a sprawling local conglomerate known for its ties to powerful politicians like Malaysia’s scandal-plagued prime minister. But lesser known is how some of the world’s largest banks have helped Rajawali — and other global agricultural powerhouses — expand their plantation empires.

The year before the clearing of trees in West Kalimantan, Rajawali’s plantation arm secured $235 million in loans — funds that the Indonesian company used to buy out a partner and bolster its landholdings — from banks including Credit Suisse and Bank of America, according to an examination of lending data by The New York Times.

The deal forms part of at least $43 billion in loans and underwriting to companies linked to deforestation and forest burning in Southeast Asia alone, according to a tally compiled by the California-based Rainforest Action Network, the Dutch consultancy Profundo and the Indonesian nongovernmental organization TuK Indonesia. More than a third of that sum comes from American, European and Japanese banks, many of which have sustainability pledges that specifically mention deforestation.

That figure is almost certainly incomplete because not all financing is made public. It also excludes loans made by the same banks to forestry projects outside Southeast Asia, or financing provided to other, more global players. And it contrasts with efforts by companies like Nestlé and Procter & Gamble to distance themselves from suppliers linked to deforestation.

And while there has been a growing movement among endowments and pension funds to divest from the fossil-fuel industry — and banks have started to back away from financing coal projects — any move away from deforestation has been slower to catch on, experts say. The role of banks has come under the spotlight in recent weeks after environmentalists called out banks like Bank of America and Goldman Sachs for financing the contentious Dakota Access oil pipeline project.

The money is aiding a process that scientists say destroys ecosystems, displaces indigenous communities and covers the region each year in a thick, suffocating smog that stretches from Jakarta to Hong Kong.

Deforestation — and the fires that frequently accompany it — also generates one-tenth of total global warming emissions, making forestry loss one of the biggest single contributors to global warming, according to the Union of Concerned Scientists.

“Destroying the world’s forests makes fighting climate change almost impossible,” said Andrew W. Mitchell, executive director of the Global Canopy Programme, a forestry think tank. “The finance sector is really lagging behind in realizing that.”

The Palm Oil Boom

In funding Rajawali’s palm oil plantations, the banks appear to have violated their own sustainability policies. In its forestry and agribusiness policy, adopted in 2008, Credit Suisse says it will not finance or advise companies with operations in “primary tropical moist forests” like those of West Kalimantan. Bank of America says in a banking policy, adopted in 2004, that it will not finance commercial projects that result in the clearing of primary tropical moist forests.

The 2014 deal financed Rajawali’s expansion into palm oil by helping the conglomerate buy out a former partner, invest in new palm oil mills and increase its landholdings. Demand for palm oil is surging worldwide, driven by rising incomes in markets like China and India and a switch away from trans fats by Americans and Europeans.

Rajawali’s plantations have been accused by environmental and labor groups of deforestation and illegal burning. Indonesia is one of the world’s biggest palm oil producers, and forestry loss there and elsewhere ranks as one of the biggest single contributors to global warming.

Sebastian Sharp, a spokesman for Rajawali’s plantation arm, acknowledged that the burning and clearing on its West Kalimantan forest sites might be illegal but said local communities encroaching on its properties and starting the fires were to blame. He said the company did not engage in illegal burning or clearing.

Credit Suisse declined to comment on its Rajawali deal or to say whether the deal violated its sustainability policies. A Bank of America spokesman, Bill Halldin, said that the most serious accusations against Rajawali came after the 2014 loan, in which the bank played “a very small role.”

“Today, we would certainly consider more information before making any decision on any client,” he said.

Brigitte Seegers, a spokeswoman for ABN Amro, declined to comment.

A Deadly Haze

Climate concerns have been brought into sharp relief by the impending presidency of Donald J. Trump, who has called climate change a hoax. Mr. Trump has said he will pull the United States out of the Paris accord, a commitment by 195 countries to take concrete measures to reduce planet-warming carbon emissions.

Daily emissions from Indonesia’s forest fires last year at times exceeded emissions produced by all economic activity in the United States. A recent Harvard and Columbia study estimated that the fires caused at least 100,000 premature deaths across Southeast Asia. The World Bank estimates that the fires cost Indonesia’s economy $16 billion.

Although deforestation has slowed in many parts of the world, notably in the Brazilian Amazon, forest clearing is on the rise in Southeast Asia. Indonesia, in particular, suffers the world’s highest rates of forest loss, an average of almost 2.1 million acres a year, a study published in 2014 found.

About 15 percent of the world’s historical forest cover remains intact, according to the World Resources Institute. The rest has been cleared or degraded or is in fragments.

Rajawali originally operated its palm plantation business, Green Eagle Holdings, as a joint venture with the French conglomerate Louis Dreyfus. But starting in 2014, Rajawali took the first step to consolidate the palm oil business under its control, and invest in new infrastructure.

Its loans from Western banks were crucial. In January 2014, Green Eagle attracted a $120 million loan from a group of lenders led by ABN Amro. In July of that year, it scored an even bigger loan of $235 million from a syndicate led by Credit Suisse. Bank of America also took part in that loan.

The financing allowed Green Eagle to buy out Louis Dreyfus to invest in new palm oil mills and increase its landholdings. In November 2014, Green Eagle merged with another plantation operator, BW Plantation; Rajawali is majority shareholder of the resulting company, Eagle High Plantations.

The banks issued those loans as Rajawali was being accused of extensive forest and peatland destruction, illegal burning, use of child labor and the use of force against workers at plantations under its control.

Land-cover mapping by the Indonesian Ministry of Environment and Forestry, and satellite imagery from Global Forest Watch, show forest loss at two sites in West Kalimantan from 2011 to 2013 and again in 2015, with much of the forest gone by the end of the year. Those sites included around 11,000 hectares of peat, which, when set alight, can smolder for months underground.

Zamzami, who goes by one name, a Greenpeace staff member in Indonesia who visited a Rajawali plantation in West Kalimantan in September 2015, said the burning continued. “It was difficult to breathe because of the smoke,” he said in field notes. “Far away, on the horizon, I could see the forest wall.”

Confronting Child Labor

Eagle High is now one of Indonesia’s largest palm oil plantation operators, with more than a million acres in land rights under its control, according to an investors’ presentation dated September 2014.

Human rights organizations have reported that children as young as 6 work to support their parents in another Rajawali-controlled plantation in the Papua province. That plantation has promised to support the abolition of child labor by ensuring that there are no children on plantation sites.

In December 2015, a 22-year-old worker was shot dead at the plantation by state security forces. It was unclear why state forces were on private property.

Mr. Sharp, the Eagle High spokesman, blamed local villagers for the forest clearing and burning on its sites. “It’s being done by local communities, and we have no control over that,” he said. Environmental groups argue that plantation companies are responsible for protecting their sites.

Mr. Sharp said that there were instances in which workers brought their children to plantations but that the company was “trying to brainstorm ways in which we can stop them from doing that.”

He also questioned the wisdom of Indonesian labor law. “Why can’t we hire children at 15? Families need income,” he said. Under the country’s law, the minimum age for hazardous work, including jobs on plantations, is 18.

The worker who was killed, Marvel Doga, was “drunk and violent, poured petrol everywhere and threatened to set fire, and he had with him a bow and arrow” when nearby state security forces tried to incapacitate him, leading to his death, Mr. Sharp said. He said Eagle High paid “thousands of dollars” to his family in compensation.

Credit Suisse and ABN Amro declined to discuss specific deals. Bank of America declined to comment on the accusations.

But in a February 2015 research note, Credit Suisse deemed Rajawali’s palm oil push a success. Eagle High’s increased landholdings and land rights signaled “significant headroom for expansion” of palm oil production, Priscilla Tjitra, an equity analyst for the bank, said in a report to clients.

“The allocation of finance is so influential in our economy and to our environment,” said Tom Picken of the Rainforest Action Network. “But there’s little way we can hold financial sectors to account.”

Running Out of Refuges

The orangutan rescues continue. The world has lost 60 percent of its population of Bornean orangutans since 1950, according to the International Union for Conservation of Nature. In July, the Bornean orangutan was listed as critically endangered.

International Animal Rescue, which runs a temporary shelter for about 100 orangutans in West Kalimantan, said its staff had rescued roughly 50 of the primates during the 2015 burning season, twice the number the organization rescues in an average year.

“They were all starving, all skinny,” said Ms. Sánchez, the orangutan rescue group’s director. So far this year, about 25 orangutans have been rehabilitated.

“The problem is that every time an area is destroyed and orangutans are under real threat, we have to look for areas to release them, and that’s challenging,” she said. “We’re running out of places where we can release these orangutans.”

In September, Rajawali’s plantation arm secured a $192 million loan from Bank Negara Indonesia, a state bank, to refinance the debt held by its plantation subsidiaries and to double the capacity of palm oil refineries in Papua and West Kalimantan.

Bank Negara Indonesia’s sustainability policies say that its clients must adopt “minimum environmental, social and governance standards.” The bank did not respond to requests for comment.