808. Ecosystem Collapse in the Anthropocene May Be Accelerated by Multiple Environmental Drivers

The climate change debate suggests that the Earth is reaching a tipping point, a point of dramatic, irreversible change caused by anthropogenic economic activity during the Anthropocene.

The tipping point is also defined as the threshold at which a small perturbation can cause a qualitative change in the state of the system. Researchers have identified the melting of the Greenland ice sheet, the thawing of permafrost, the melting of the Antarctic ice sheet, and deforestation in the Amazon as large-scale subsystems that are likely to cross the tipping point. The concern is that a tipping point in one subsystem will spread to other subsystems, causing a domino effect.

About 20 years ago, it was thought that a major discontinuity in the climate system would occur if warming exceeded 5°C relative to the industrial revolution. However, recent discussions suggest that the tipping point could occur at a temperature increase of 1-2°C, and in response, the Paris Agreement is moving toward limiting warming to less than 2°C and, if possible, less than 1.5°C.

When researchers evaluate how the tipping point is reached in a real-world model, they are concerned with how to handle feedbacks between stresses and drivers from multiple anthropogenic activities that cause changes in the system. Intuitively, one would expect that the higher the level of stress and the greater the number of stresses and disturbances, the shorter the time to reach the threshold of ecosystem collapse. Using the Amazon as an example, we can imagine that deforestation is the first step, then global warming is added to deforestation, and then disturbances from extreme events such as droughts and wildfires are added, and these feedbacks also accelerate ecosystem collapse. On the other hand, such studies and evidence are extremely limited.

In response to this awareness, a paper published on June 22 in Nature Sustainability warned of the possibility of even earlier ecosystem collapse due to the interplay of multiple stresses, including warming from anthropogenic economic activities, environmental impacts, and disruptive factors such as extreme events.

Instead of tipping points, the paper focuses on abrupt threshold-dependent changes (ATDCs), which indicate quantitative and qualitative collapse of the system from its ideal state. The dynamics of the interactions among multiple environmental stresses that lead to abrupt changes in the system are then examined in four ecosystem models that illustrate the complex effects of anthropogenic impacts: Lake Chilika model on fish population; Easter Island model on human population; TRIFFID model on tree cover; and Lake Phosphorus model on lake phosphorus concentration. The results suggest that ecosystem collapse may be 38-81% faster as key environmental stresses intensify and multiple stresses and disturbances are added. On the other hand, the results showed that the impact of major and other stresses on the system varies from system to system.

The paper suggests that while ecosystems may be degrading at a faster rate than we assume, the impact and history of stress interdependencies will vary from system to system, underscoring the need for research that considers a wide range of situations when addressing tipping points in the real world.

Reference
Willcock, S., Cooper, G.S., Addy, J. et al. Earlier collapse of Anthropocene ecosystems driven by multiple faster and noisier drivers. Nat Sustain (2023). https://doi.org/10.1038/s41893-023-01157-x

Contributor: IIYAMA Miyuki (Information Program)