Once vital barriers to climate change, Amazonia’s forests now show how that and other human action can harm the rainforest.
LONDON, 11 August, 2021 − Part of Brazil − home to the world’s greatest rainforest − is becoming a source of greenhouse gases. What had once been a powerful machine in the climate system for absorbing carbon dioxide and cooling the planet is now playing a role in accelerating climate change. Much of Amazonia’s forests are no longer carbon sinks: now they are sources instead.
Why? Drought, and forest fires made increasingly likely by drought, have lately killed an estimated 2.5 billion trees and vines, to turn what had once been forest too wet to catch fire into a tinderbox.
And the process is not likely to stop as human numbers multiply and global temperatures soar. Yet another study has found that even those parts of the tropical forest worldwide that are defined as “intact” are at risk: mining, quarrying and extractive industries have concessions that overlap with at least a fifth of the world’s remaining tropical forest.
In the first 13 years of this century alone, an estimated 919,000 sq kms of forest − an area the size of Nigeria − was degraded, destroyed or converted. The area of surviving forest now identified as at risk is 975,000 sq kms, an area almost the size of Egypt.
The restoration and conservation of the world’s forests is a vital part of the global strategy to contain and limit climate change: all three studies confirm the worst fears of conservationists and climate scientists.
East-West split
Researchers have repeatedly warned that what had once been a vast, rich rainforest could − as global temperatures rise and human demands multiply − collapse to something more like dry savannah.
The latest study, in the journal Nature, is a progress report on an ecological catastrophe. Researchers flew 590 missions from four locations above the forest between 2010 and 2018 to make precise measurements of carbon dioxide and carbon monoxide released from stressed and damaged vegetation below.
They found that eastern Amazonia on the whole surrendered more carbon than the forest to the west: over the past 40 years, this region has been more systematically invaded, felled, burned and baked by rising temperatures.
South-eastern Amazonia, in particular, now releases more carbon than it absorbs. Carbon that had once been stored in timber, foliage and soils is now escaping into the atmosphere to make climate change even more hazardous. Researchers estimate that the entire forest is home to 123 billion metric tons of carbon: as more escapes, so much the higher the planetary thermometer could rise.
“It is almost impossible to restore the myriad values of intact forests once they are lost”
And extreme drought and extended wildfires will be among the agents that do the damage, according to a new study in the Proceedings of the National Academy of Sciences. Researchers looked at a tract of forest about twice the size of Belgium in eastern Amazonia − it would amount to just 1.2% of the entire Brazilian Amazon rainforest − after the drought triggered by a largely natural climate phenomenon known as El Niño in 2015 and 2016.
They calculate that drought and fire accounted for 2.5 billion trees and shrubs, and the loss of these released 495 million tonnes of carbon dioxide into the air above them. Although, as the rains resumed, the vegetation started to recover, three years later only about a third of the emitted carbon dioxide had been re-absorbed.
But drought and wildfire are not the only agents of destruction: human intrusion is even more destructive, and tends to change the forest forever.
The Wildlife Conservation Society and the WorldWide Fund for Nature report in the journal Frontiers in Forests and Global Change that the extractive industries authorised by governments have gained concessions over huge areas of what conservationists define as tropical intact forested landscapes; that is, the jungles of the Amazon and the Congo, and South-east Asia.
Avoiding disturbance
These intact forests store around two-fifths of all tropical forest carbon, and at least a third of their area is home to − and is protected by − groups recognised as politically and economically marginalised indigenous people.
So undisturbed forest is important for the myriad as-yet-unidentified wild plants and animals that define an ecosystem; it is also an important part of the human mosaic.
The study is only a first measure of the risk to the remaining tropical wilderness. Although extractive industries are more interested in the oil, gas and minerals that lie beneath the forest floor, they depend on roads, pipelines and power lines, housing settlements and supply chains that divide and disturb what had once been wilderness.
That triggers a cascade of other consequences. Loss and disturbance become inevitable and may be permanent. As the researchers point out: “It is almost impossible to restore the myriad values of intact forests once they are lost.” − Climate News Network