Illegal logging on Pirititi indigenous lands in the Brazil’s Amazon rainforest adds to the impact of longer and hotter dry seasons. Image: Felipe Werneck/Ibama via flickr
In less than a human lifetime, the world’s greatest rainforest could become parched grassland and scrub, and the Caribbean coral reef system could collapse completely.
The entire Amazon rainforest could collapse into savannah – dry grassland with scrub and intermittent woodland – within 50 years as a result of human action.
And the study of what it takes to alter an enduring natural ecosystem confirms that, within as little as 15 years, the rich Caribbean coral reef system could be no more.
A new statistical examination of the vulnerability of what had once seemed the eternal forest and the glorious coral reefs confirms that once large ecosystems begin to change, they can reach a point at which the collapse becomes sudden and irreversible.
The research confirms an increasing fear that global heating driven by profligate human use of fossil fuels could tip not just climate but also natural landscapes into a new and potentially catastrophic states.
More directly, as reported in an interview with Brazilian scientist Antonio Donato Nobre in Climate News Network yesterday, it confirms a dramatic warning delivered in December last year that the Amazon rainforest – a landscape almost as vast as the entire 48 contiguous states of the US – may already be teetering on the edge of functional disruption.
How this disruption could happen was recently outlined by two scientists, Thomas Lovejoy, professor of biology at George Mason University in Virginia, US, and Carlos Nobre, a leading expert on the Amazon and climate change, who is the brother of Antonio Donato Nobre and is senior researcher at the University of Saõ Paulo’s Institute for Advanced Studies.
Lovejoy and Carlos Nobre point out that most of the rain that keeps the Amazon a rainforest is actually recycled from the dense canopy that covers the region. After rainfall, evapotranspiration from the foliage returns water vapour to the air above the forest and falls anew as rain, again and again.
“Over the whole basin, the air rises, cools and precipitates out close to 20% of the world’s river water in the Amazon river system,” they warn in a Science journal report.
“Current deforestation is substantial and frightening: 17% across the entire Amazon basin and approaching 20% in the Brazilian Amazon.
“Already there are ominous signals of it in nature. Dry seasons in the Amazon are already hotter and longer. Mortality rates of wet-climate species are increased, whereas dry-climate species are showing resilience. The increasing frequency of unprecedented droughts in 2005, 2010 and 2015/16 is signalling that the tipping point is at hand.”
By contrast, the latest study in Nature Communications zeroes in on the rates at which large ecosystems could, in principle, change once the climate has begun to shift and the natural habitat is in some way degraded.
“This is yet another strong argument to avoid degrading our planet’s ecosystems; we need to do more to conserve biodiversity.”
Three scientists in the UK used computer models to test data from four terrestrial landscapes, 25 marine habitats and 13 freshwater ecosystems. They found, not surprisingly, that larger ecosystems tend to undergo regime shifts more slowly than the smaller ones.
However, as the ecosystem gets bigger, the additional time taken for collapse to happen gets briefer, so big ecosystems fail relatively more quickly.
This would mean that it would take 15 years for 20,000 sq km of Caribbean reef system to collapse, once some fatal trigger point had been reached. And the 5.5 million sq km of the Amazon tropical moist forest, once it starts to go, could be gone in just 49 years.
“Unfortunately, what our paper reveals is that humanity needs to prepare for change far sooner than expected,” says Simon Willcock, senior lecturer in environmental geography at Bangor University in Wales.
And his colleague, Dr Gregory Cooper, postdoctoral research fellow at the University of London’s Centre for Development, Environment and Policy, says: “This is yet another strong argument to avoid degrading our planet’s ecosystems; we need to do more to conserve biodiversity.”
Other researchers have separately found that the Amazon rainforest could be about to become a source of yet more atmospheric carbon – rather than a green machine for absorbing surplus carbon dioxide from the atmosphere – as a result of climate change and environmental destruction.
The Amazon ecosystem took 58 million years to evolve. But the message is that it could unravel in a very short time.
Alexandre Antonelli, director of science at the Royal Botanic Gardens at Kew, London, was not one of the researchers, but he describes the results of the study as “terrifying” and warns that the Amazon could pass the point of no return this year.
He says: “Nature is fragile. Just because an area is big or a species is common, it doesn’t mean they’ll last forever.
“The Sahel – an area south of the Sahara that is six times the size of Spain – went from being vegetated and bountiful to just a desert in a few hundred years.
“The American chestnut – one of the most important trees of eastern North America – almost faced extinction after a fungal disease caused some three to four billion trees to die in the early 1900s.
“Natural ecosystems are usually resilient to change when kept intact, but after decades of disruption, exploitation and climatic stress, it should come as no surprise that they are breaking down.
“In other words, you can’t simply remove huge chunks of a rainforest and hope everything will be fine – it won’t. Based on these results, 2020 is our very last opportunity to stop Amazonian deforestation.” – Climate News Network
About the Author
Tim Radford is a freelance journalist. He worked for The Guardian for 32 years, becoming (among other things) letters editor, arts editor, literary editor and science editor. He won the Association of British Science Writers award for science writer of the year four times. He served on the UK committee for the International Decade for Natural Disaster Reduction. He has lectured about science and the media in dozens of British and foreign cities.
Book by this Author:
Science that Changed the World: The untold story of the other 1960s revolution
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