By John Dearing, Gregory Cooper, Simon Willcock
All over the world, tropical rainforests are turning into savanna or farmland; the savanna dries up and turns into desert; and the freezing tundra thaws. Indeed, scientific studies have now recorded such “regime shifts” in more than 20 different types of ecosystems, where tipping points have been crossed. Worldwide, more than 20% of ecosystems are at risk of changing or collapsing.
These collapses could happen sooner than we think. Humans are already subjecting ecosystems to many pressures, which we call “stress”. If we add to these pressures an increase in climate-related extreme weather events, the date when these tipping points would be crossed could be advanced by 80%.
This means that an ecosystem collapse that we could have hoped to avoid until the end of this century could occur as early as the next few decades. This is the grim conclusion of our latest research, published in Nature Sustainability (“Earlier collapse of Anthropocene ecosystems driven by multiple faster and noisier drivers,” June 22, 2023).
Human population growth, increasing economic pressure and greenhouse gas concentrations put pressure on ecosystems and landscapes to provide food and maintain essential services such as water drinkable. The number of extreme weather events is also increasing and it will only get worse.
What really worries us is that climate extremes could hit ecosystems already stressedwhich in turn would transmit new stresses or increased to another ecosystem, and so on. This means that a collapsing ecosystem could have a ripple effect on neighboring ecosystems through successive feedback loops: a “fatal ecological loop” scenario with catastrophic consequences.
How long before the collapse?
In our new research, we wanted to get an idea of how much stress ecosystems can withstand before collapsing. To do this, we used models, that is, computer programs that simulate the future functioning of an ecosystem and its reaction to changing circumstances.
We used two general ecological models representing forests and lake water quality, and two specific models representing fisheries in the Chilika Lagoon, Indian state of Odisha. [est de l’Inde], and Easter Island (Rapa Nui), in the Pacific Ocean. These last two models explicitly include the interactions between human activities and the natural environment.
The main characteristic of each model is the presence of feedback mechanisms, which help to maintain the balance and stability of the system when the stresses are low enough to be absorbed. For example, Chilika Lake fishermen tend to prefer to catch adult fish when the fish stock is abundant. As long as there are enough adults left to reproduce, the situation is stable.
However, when the stresses can no longer be absorbed, the ecosystem abruptly crosses a point of no return – the tipping point – and collapses. In Chilika, this can happen when fishermen increase catches of young fish in times of scarcity, further compromising the renewal of the fish stock.
We have used the software to model over 70,000 different simulations. In all four models, combinations of stress and extreme events advanced the date of the predicted tipping point by 30-80%.
This means that an ecosystem predicted to collapse in the 2090s due to the gradual increase of a single source of stress, such as global temperatures, could, in the worst case, collapse in the 2090s. 2030s if we take into account other problems such as extreme rainfall, pollution or a sudden increase in the use of natural resources.
Importantly, about 15% of ecosystem collapses in our simulations occurred as a result of novel stresses or extreme events, while the main stress remained constant. In other words, even if we think we are managing ecosystems sustainably by keeping key levels of stress constant – for example, by regulating fish catches – we had better keep an eye out for new stresses and extreme events. .
There is no ecological “bailout”… like the banks
Previous studies have suggested that exceeding tipping points in large ecosystems will incur significant costs beginning in the second half of this century. But our results suggest that these costs could arise much earlier.
We found that the rate at which stress is experienced is key to understanding system collapse, which is likely relevant for non-ecological systems as well. Indeed, the increased speed of media coverage and digital banking processes has recently been cited as raising the risk of bank collapse. [retraits numériques massifs et ultra-rapides des avoirs]. As noted by journalist Gillian Tett (Financial Times, April 27, 2023): “The collapse of Silicon Valley Bank provided a terrifying lesson in how technological innovation can change finance in unexpected ways (in this case by intensifying digital behavior). The recent flash crashes offer another. However, this is probably a small taste of the future of viral feedback loops.”
But the comparison between ecological and economic systems stops there. Banks can be saved as long as governments provide sufficient liquidity for bailouts. In contrast, no government can provide the immediate natural capital needed to restore a collapsed ecosystem.
There is no way to restore collapsed ecosystems in a reasonable time. There is no green bailout. In financial jargon, we will simply have to “take the hit”. (Article published on the website The Conversation, June 22, 2023; translation writing Against)
John Dearing, Professor of Physical Geography, University of Southampton; Gregory Cooper,Postdoctoral Research Fellow in Socio-Ecological Resilience, University of Sheffield; Simon WillcockProfessor of Sustainable Development, Bangor University (Wales)
