Tim Lenton - Climate tipping points

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Tim Lenton, Professor of Earth System Science at the University of Exeter, explains climate tipping points, when we may hit them and warning methods.

About Tim Lenton

"I’m Director of the Global Systems Institute and Professor of Earth System Science at the University of Exeter. My work focusses on the transformation of our planet.

Reading Jim Lovelock’s books on Gaia ignited my passion for studying the Earth as a whole system. I study how our remarkable planet came to be the way it is now. I study how humans are transforming the Earth’s system and how we might create a flourishing future within that system."

Tipping points are something that can happen in a whole range of complex systems, including the human body and the entire Earth climate system, or “Earth system”. A tipping point is where a small nudge to a system has a huge outcome. It changes the state or the fate of that system. You could say that a heart attack or death were the bleakest tipping points for the human body; but, in all cases, the crucial thing is that within complex systems, there are cycles. There are closed loops of causality; there are things that scientists call feedbacks. Some of these feedbacks amount to amplifiers.

And that’s what’s driving change.

Identifying the different kinds of climate tipping points
There are many potential tipping points in the climate system that human activities are currently causing and could potentially tip for the rest of this century.

A first class of tipping points includes the melting of the great ice sheet on Greenland, on West Antarctica and parts of the East Antarctic ice sheet. A second category of tipping points involves the biosphere: the possibility that we could tip a dieback of the Amazon rainforest or the great forests that cloak the northern high latitudes – the boreal forests – or a major loss of coral reefs in the tropical oceans. Finally, there’s a third class of tipping points, which would involve reorganising aspects of the circulation of the ocean and the atmosphere, and how they’re coupled together.

Key Points

• Like any complex system, the parts of the Earth system are interconnected. A tipping point is where a small nudge to a system has a huge outcome. It changes the state or the fate of that system.
• There are three main kinds of climate tipping points: a first includes the melting of the great ice sheets; a second involves a major loss of the biosphere; a third involves the circulation of the ocean and the atmosphere, and how they’re coupled together.
• When various tipping points interact in a domino effect, it’s called a “tipping cascade” – and this is what we must avoid at all costs.
• We expect some tipping points to be triggered at different levels of warming and that’s the strongest reason, to try and limit global warming, which means stopping fossil fuel burning as soon as possible.

Like any complex system, the parts of the Earth system are interconnected. That’s also true of the climate tipping points that I and others have identified. We know, for example, that as the Greenland ice sheet is melting and fresh water is pouring into the North Atlantic Ocean on either side of Greenland, that this makes the surface waters of the ocean less dense, less salty and less prone to sinking to the bottom of the ocean. We call this extraordinary process: "deep convection of ocean waters".