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©Johan van de Koppel / Ulco Glimmerveen

Earth is more resilient than was thought

We have to do all we can to stop climate change. But: the Earth is more resilient than we thought. That is the surprising conclusion of an international team of ecologists and mathematicians, which included Leiden mathematician Arjen Doelman. The team discovered that ecosystems can still avoid tipping points caused by climate change. They have published their findings in the journal Science.

We are regularly warned that climate change can lead to tipping points: irreversible situations in which the shift from savannah to desert or the Gulf Stream slowing down happens at an accelerated pace. Spatial patterns are often referred to here as harbingers of such tipping points. The team of ecologists and mathematicians looked at these patterns from a spatial context and discovered that this pattern formation means that ecosystems can avoid these tipping points.

Turing patterns as warning sign

‘Spatial pattern formation in ecosystems, such as when complex patterns occur spontaneously in vegetation, are often interpreted as an early warning sign for a critical transition,’ says principal researcher Max Rietkerk, an ecologist from Utrecht University. The international research team, which is the result of years of collaboration between Utrecht University and Leiden University in particular, based its conclusions on mathematical analyses of spatial models and on new warnings in real ecosystems.

A computer simulation of a tidal sandbank, based on mathematical models.
Spatial pattern formation caused by algae and mussels on a tidal sandbank. This pattern formation means that tipping points caused by rising sea levels can be avoided, so the sandbanks do not become submerged. The spatial patterns on the tidal sandbank, including the ripples, are based on mathematical model simulations. ©Johan van de Koppel / Ulco Glimmerveen

Pattern formation a sign of resilience

Spontaneously occurring patterns in nature are often called Turing patterns, after the famous British mathematician Alan Turing. In 1952 he described how patterns in nature, such as spots and stripes on an animal’s skin, could occur from a uniform starting position. ‘In ecology these Turing patterns are often interpreted as warning signs because they could point to a disruption in an ecosystem,’ explains Leiden mathematician and co-researcher Arjen Doelman. ‘Our analysis now shows, however, that the fact that pattern formation occurs somewhere, doesn’t necessarily mean that an equilibrium has been disturbed to past a tipping point.’ 

Rietkerk gives an example. ‘At the transition from savannah to desert, you see all sorts of complex spatial forms. A spatial reorganisation therefore, but not necessarily tipping points. On the contrary, these Turing patterns are actually a sign of resilience.’

Avoid tipping points

The researchers discovered an interesting phenomenon: multistability. This means that many different spatial patterns can simultaneously occur under the same conditions. Rietkerk: ‘Each of these patterns can remain stable under a wide range of circumstances and climate change. In addition we can now see that each complex system that is large enough to generate spatial patterns may be able to avoid tipping points.’ The question should therefore be: which systems are sensitive to a tipping point and which ones are not? ‘For the exact role of tipping points, we therefore have to go back to the drawing board,’ says Rietkerk. ‘Only then can we determine which conditions and spatial patterns lead to tipping points and which ones do not.’

The article Evasion of tipping in complex systems through spatial pattern formation was published in Science on 8 October.

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