The capacity of re-grown areas of the Amazon rainforest to draw carbon dioxide from the atmosphere and combat climate change may have been “vastly overestimated”, scientists fear.

The forest is a gigantic carbon sink, drawing the greenhouse gas from the atmosphere. Cleared areas that are re-planted are known as secondary forest, and have been seen as key to fighting climate change, researchers at Lancaster University said.

But a new study has found that those areas held just 40 per cent as much carbon dioxide as sequestered by parts of the Amazon untouched by humans, casting doubt on their ability to aid in mitigating the crisis.

And at the same time, global warming appeared to be hampering the re-growth of secondary forest.

Scientists monitored forest regrowth over a period of 20 years and revealed how the Amazon was affected by periods of drought. During times of “water deficit”, regrown forests absorb less carbon from the atmosphere.

“If current trends continue, it will take well over a century for the forests to fully recover, meaning their ability to help fight climate change may have been vastly overestimated,” Lancaster University said.

Amazon rainforest swept by fires: In pictures Show all 25 1 /25 Amazon rainforest swept by fires: In pictures Amazon rainforest swept by fires: In pictures Fire rages in the Amazon rainforest in the Brazilian state of Rondonina on August 23 Reuters Amazon rainforest swept by fires: In pictures Smoke billlows from burning tracts of the Amazon rainforest in the Brazilian state of Para on August 23 AFP/Getty Amazon rainforest swept by fires: In pictures Fire rages in the Amazon rainforest in the Brazilian state of Rondonina on August 23 EPA Amazon rainforest swept by fires: In pictures Land in the Amazon rainforest left scorched in the fires in the Brazilian state of Rondonina on August 23 AFP/Getty Amazon rainforest swept by fires: In pictures Smoke billows during a fire in an area of the Amazon rainforest in the state of Rondonia, Brazil on August 23 AFP Amazon rainforest swept by fires: In pictures Fire tears through a farm in the Brazilian state of Mato Grosso AP Amazon rainforest swept by fires: In pictures An area of the Amazon rainforest left scorched in the fires in the Brazilian state of Amazonas on August 24 AFP/Getty Amazon rainforest swept by fires: In pictures Satellite images show a series of fires in the southwest Brazilian state of Rondonia on August 15 AP Amazon rainforest swept by fires: In pictures Smoke billows during a fire in an area of the Amazon rainforest in the state of Rondonia, Brazil Reuters Amazon rainforest swept by fires: In pictures A satellite image released by NASA shows the active fires that have been detected in the Amazon region EPA Amazon rainforest swept by fires: In pictures Smoke billows during a fire in an area of the Amazon rainforest in the state of Amazonas, Brazil Reuters Amazon rainforest swept by fires: In pictures Smoke billows during a fire in an area of the Amazon rainforest in the state of Rondonia, Brazil Reuters Amazon rainforest swept by fires: In pictures Smoke billows during a fire in an area of the Amazon rainforest in the state of Rondonia, Brazil Reuters Amazon rainforest swept by fires: In pictures Smoke billows during a fire in an area of the Amazon rainforest in the state of Amazonas, Brazil Reuters Amazon rainforest swept by fires: In pictures Indigenous people from the Mura tribe wallk in a deforested area inside the Amazon rainforest in the Brazilian state of Amazonas on August 20 Reuters Amazon rainforest swept by fires: In pictures Fire tears through a farm in the Brazilian state of Mato Grosso AP Amazon rainforest swept by fires: In pictures Smoke billows from a stretch of fire in the Amazon rainforest in the Brazilian state of Rondonia on 23 August AFP/Getty Amazon rainforest swept by fires: In pictures Smoke billows during a fire in an area of the Amazon rainforest in the state of Amazonas, Brazil Reuters Amazon rainforest swept by fires: In pictures Indigenous people from the Mura tribe wallk in a deforested area inside the Amazon rainforest in the Brazilian state of Amazonas on August 20 Reuters Amazon rainforest swept by fires: In pictures Smoke billows from a stretch of fire in the Amazon rainforest in the Brazilian state of Rondonia on 23 August AFP/Getty Amazon rainforest swept by fires: In pictures A view of logs felled illegally in the Amazon rainforest are seen in sawmills in the Brazilian state of Amazonas on August 22 Reuters Amazon rainforest swept by fires: In pictures A scorched patch of land in the state of Mato Grosso in Brazil on 20 August EPA Amazon rainforest swept by fires: In pictures Several fires are seen burning in the Amazon rainforest in this satellite image taken by NASA on 11 August AFP/Getty Amazon rainforest swept by fires: In pictures Smoke billows from a stretch of fire in the Amazon rainforest in the Brazilian state of Rondonia on 23 August AFP/Getty Amazon rainforest swept by fires: In pictures The sunsets behind clouds and smoke from fires in the Amazon rainforest in the Brazilian state of Rondonia on 18 August EPA

Increased temperatures from global warming are in turn causing more drought-years in the Amazon, therefore limiting the capabilities of the secondary forests to help beat carbon pollution.

Led by a group of Brazilian and British researchers, the study also found that even after 60 years, regrown forests held only two-fifths as much carbon as virgin forests.

It could take more than a century for the forests to fully recover and “reduce the effectiveness of climate mitigation strategies in regions that have a long history of human occupation”.

Author Fernando Elias, of the Federal University of Para, said: “The region we studied in the Amazon has seen an increase in temperature of 0.1C per decade and tree growth was lower during periods of drought.

“With predictions of more drought in the future, we must be cautious about the ability of secondary forests to mitigate climate change. Our results underline the need for international agreements that minimise the impacts of climate change.”

Scientists also found there to be a “near-zero increase” in biodiversity within these secondary forests between 1999 and 2017.

Forests are vital habitats for threatened species and ecosystems, but results from the study show poor biodiversity relationships in highly-deforested landscapes.

“It is also likely that we are overestimating the relative recovery of biodiversity,” added the study.

Joe Barlow, professor of conservation science at Lancaster University and also an author of the study, said secondary forests’ potential to mitigate climate change was of “global importance”.