Science - December 25, 2011

Evidence for tipping point theory

Wageningen scientists have proven the existence of tipping points in a living system. Their publication appears in Nature.

101wuCyanobacterien_ecosysteem.jpg
Complex systems sometimes take on a completely new form when their state of balance is upset. For example, clear lakes suddenly become murky. That happens when a so-called tipping point is exceeded. This pioneering theory was published two years ago by Marten Scheffer's Aquatic Ecology and Water Quality Management Group. 
Blue-green algae
Now for the first time, empirical evidence has been provided. PhD student Annelies Veraart from Scheffer's group proved this phenomenon in a tank with cyanobacteria (blue-green algae). The bacteria in the tank - a small ecosystem - were exposed gradually to more and more light. This took place until a critical point was reached and the population collapsed due to excessive light. 
Delay
At the core of the tipping point theory is the phenomena called 'critical slowing down'. This means that systems which are getting close to their tipping points take a longer time to recover when they are thrown out of balance. Veraart interrupted her system by removing ten percent of the bacteria population every four days. Veraart: 'We saw that the population recovered slower as the light became stronger and the tipping point came closer.'
Milestone
The empirical evidence is a major new milestone in the research carried out by Scheffer's group. 'We are now confident that there are possibilities that the theory can be made more suitable for application.' Scheffer has earlier demonstrated that warning signs appeared prior to big climate shifts in the history of the earth.

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