Before briefly considering the climate crisis and tipping points, consider the tipping point of a wine glass standing on a bench.

The tipping point of a wine glass

What happens when you push the top of the glass with your finger, and the glass leans more and more, like the leaning tower of Pisa.

State 1: The wine glass standing on its base

The wine glass is standing on its base on a table. When you push it a little with your finger, and then remove your finger, the glass will return to standing. This is because gravity holds the glass against your finger, even as you withdraw your finger, and the glass moves back to standing. Gravity is assisting this stability

The glass standing on its base is in a state of stable equilibrium.

State 2: The finger-tilted glass

As your finger pushes the glass onto an angle, you are supporting some of the weight of the glass with your pushing finger. It takes less and less pushing to move the glass as more and more the glass comes to support its own weight via the base of the glass alone.

State 3: The tipping point

At the tipping point, the glass comes into balance and you no longer have to push the glass at all to keep it tilted. In theory, you could remove your finger and the glass would stay there delicately balanced all by itself.

However, you now have the glass in a state of delicate balance, and the slightest vibration or wind could destabilize it. It is in a state of equilibrium, but this is an unstable equilibrium.

State 4: The falling glass

Once your finger pushes the glass past the tipping point, the glass becomes over-balanced and it starts falling.

As the glass leans further, more and more of the weight acts to topple the glass. So the glass accelerates into the fall, with increasing acceleration as it falls.

A radical change occurs when you move past the tipping point

When you move past the tipping point, there is an important change.

• Before you reach the tipping point you can return the glass to standing by reversing your finger pushing. This is because gravity is still a force for stability and it pushes the glass to sit on its base again as you remove your finger.
• Beyond the tipping point, when the glass starts falling, gravity is acting to increase the tipping. Now if you stop pushing the glass with your finger, it makes no difference.
• To return the glass to standing, you have to do something different. You could save the glass by catching it.

To keep a productive system, it is important not to push it past a tipping point.

Tipping points and climate crisis

We have been pushing our climate by increasing the CO2 levels in the atmosphere and so heating the planet. We are currently hoping that decreasing the CO2 in the atmosphere can bring temperatures down again. However, if we push past a tipping point, reducing CO2 levels will no longer have an impact. This is just like once the glass passes its tipping point, withdrawing the pushing finger has no impact.

This could be because melting ice starts releasing large quantities of methane into the atmosphere, and the warming impact of this methane exceeds the rate at which humans can reduce the warming impact of CO2 in the atmosphere. We would be left on a planet that keeps on heating and we could not influence this.