What tipping point are climate scientists most worried about?

Collapsing ice sheets, loss of the Amazon rainforest, melting permafrost.……. Key parts of Earth's climate system are in trouble. Which could trigger disaster first?

- PROF BILL MCGUIRE

If you want to make a climate scientist uncomfortable, just sidle up to them and whisper "tipping points" in their ear. Climate breakdown driven by global heating is scary enough, but so-called climate tipping points send a shiver down the spine. So, what are they and why do they have us all running scared? We're in the middle of a unique experiment that's driving up the global average temperature at least 10 times faster than at any time in the geological record.

The consequences are all around us: explosions of extreme weather, collapsing ice sheets and accelerating sea-level rise.

But as greenhouse gas emissions continue to climb as fast as ever and the global temperature rise (compared to pre-industrial times) for the last 12 months touches 1.64°C (a rise of almost 3°F), so the likelihood of sudden, permanent switches in dangerous elements of the climate system is becoming increasingly possible.

Because a critical threshold needs to be reached before a switch can occur, and because like a tilting seesaw - once a switch starts, there's no going back, they're called tipping points.

There are plenty of definitions out there, but the one that really hits the nail on the head comes from The American Heritage Dictionary of the English Language, which describes a tipping point as: "A critical moment in a complex situation in which a small influence or development produces a sudden large or irreversible change." Where the climate is concerned, for large, read disastrous.

How things could tip

Scientists who work to model where global heating is taking our climate struggle with tipping points for two reasons. Firstly, they're not easy to pin down in terms of timing and impact.

Secondly, how tipping points are treated within climate models can dramatically influence the output, thereby increasing uncertainty in terms of forecasting how climate breakdown will unfold in years to come.