A climate change activist holds a placard to highlight environment hazards, deforestation and wildfires of the Amazon forest outside the Brazilian Consulate General in Mumbai, India, August 23, 2019. Photo: Xinhua

If governments follow through on plans to build thousands of kilometers of roads through the Amazon, the world's largest tropical rainforest, it will not only fuel deforestation but bring economic losses too, researchers said on Monday.

They examined the potential social, environmental and economic impact of 75 roads, totaling 12,000 kilometers, slated for construction in the remote Amazon basins of Brazil, Bolivia, Colombia, Ecuador and Peru over the next five years.

Governments are set to spend $27 billion on constructing roads mainly to boost agriculture, including cattle-ranching and soybean production in Brazil, according to a study published in the Proceedings of the National Academy of Sciences journal.

Yet 45 percent of the proposed road infrastructure projects would result in economic losses, the researchers estimated.

That means the initial investment and maintenance costs would be larger than the benefits - measured as reduced transportation costs - over a 20-year period, they said.

Canceling those road projects would avoid a loss of $7.6 billion, the economists calculated.

Study coauthor Alfonso Malky said many of the new road projects lacked "basic economic feasibility analyses" and did not have traffic estimations, the most important variable in determining their economic benefits.

Malky, who is Latin America technical director of the Conservation Strategy Fund, a global environmental group, said some of the 75 road projects examined also failed to properly address the social and environmental impacts of such development.

Scientists consider the Amazon forest as the key to the fight against climate change because of the vast amounts of planet-warming carbon it stores.

With rising deforestation rates, particularly in Brazil - home to the biggest share of the Amazon - protecting the rainforest is an urgent priority, they say.

The study found that if all the planned roads were built, at least 2.4 million hectares of Amazon forest would be cleared in the next 20 years. Brazil would see the highest rates of deforestation, followed by Colombia.

In Brazil, for example, proposed projects to improve its 2,234-kilometer trans-Amazonian highway (BR-230) would cause forest-cover loss amounting to nearly a quarter of the total predicted for the region by 2030, the study said.

"We have a lot of examples of roads that were built in the Amazon that are kind of environmental disasters and they affect negatively on the well-being of people," Malky told Reuters.

Researchers also identified 18 road projects with the lowest social and environmental impacts.

If governments implemented only those projects while halting the rest, it would generate a net gain of $4 billion and result in less than 10 percent of the projected deforestation, they found.

Lead author Thais Vilela said all roads would have a negative effect on the environment, but states could choose to build only those with less harmful consequences.

"Governments, together with society and other stakeholders, should decide what is the level of negative environmental impact that's acceptable in exchange for economic benefits," she added.