Sergey Buldyrev

A study from Sergey Buldyrev and colleagues was published in Nature the day before Eyjafjallajökull’s eruption. The researchers investigated catastrophic failures in complex networked systems—systems like the closely coupled infrastructures underlying modern transportation, electricity distribution, telecommunications, and financial transactions. These systems are constructed from many interdependent nodes, which gives them greater stability and resilience: If one node fails, material, money, energy, or people are routed through other nodes, and functionality is maintained. But past a certain critical threshold of node failures, the system fragments and cannot function.

Buldyrev’s team modeled how disruptions percolate through a tightly linked pair of idealized interdependent networks, and found a counter-intuitive result: The failure of even a small number of nodes in one network can cause additional failures in the second. These failures can then feed back into the first network and cause yet more node failures. In other words, the greatest strength of an interdependent network in isolation is also the greatest weakness of interdependent networks as a whole. Two closely linked, highly resilient systems can suffer catastrophic failure through initially small disruptions that would have been essentially harmless to either network individually. What’s true for two linked networks presumably holds for larger assemblages.

A better message for Earth Day would be more frightening, and closer to the truth: save the humans. The planet will endure our collective ravages and the biosphere will eventually rebound. The world has certainly changed over the past forty years, but we have changed even more. As the products of countless interdependent complex systems, we seem to somehow harbor their flaws. Now, we’re making them manifest, eliminating the interstices that used to protect and insulate the thin veneer of life that glosses this planet. Our greatest strength has become our greatest weakness; we are complex, but fragile. Our systems are connecting, with each node at our fingertips. Alas, if only their failures could teach us to fly.