Tipping the balance

Tipping points abound in nature – you can hardly go anywhere without tripping over them. Nature is dynamic. Nature is often nonlinear. Nature is complex and interconnected. All of these features can create tipping points.

In many cases tipping points are trivial. Warm a single ice cube by just a tiny amount, from just below freezing (say, -0.01ºC) to just above it (0.1ºC) and presto! Your ice cube becomes a little puddle. In this context the melt is inconsequential, but imagine crossing the same tiny temperature threshold in Siberia, where some 11 million square kilometres of land – an area the size of France and Germany – are locked up in permafrost.

The Siberian permafrost contains hundreds of billions of tonnes of carbon, which has slowly accumulated as frozen peat during many millennia. The peat hasn’t decomposed because there is no freestanding water, which is crucial for soil microbes.

When the permafrost melts, however, the microbes leap into action, consuming the peat and emitting as waste products methane and carbon dioxide – both potent greenhouse gases. Suddenly, many billions of tonnes of carbon emissions flood into the atmosphere. Global temperatures...

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