Lecture 6 - Abrupt Climate Change

Question 1

What is a positive and negative coupling?

Answer 1

A coupling is a change (increase or decrease) in one component that leads to change (same or opposite direction) in another component.

A positive feedback results in abrupt transition and tipping points.

A negative feedback results in stability and homeostasis.

Question 2

What is the definition of a tipping point?

Answer 2

A tipping point is a critical threshold at which the future state of system can be qualitatively altered by a small change in forcing.
→ Vegetation feedbacks & ice-feedbacks important

Question 3

Explain Stable & unstable equilibria

Answer 3

Stable equilibrium is associated with negative feedbacks as disturbance is followed by a
responses that returns the system back to its equilibrium state.

Unstable equilibrium is associated with positive feedbacks as they are more vulnerable.

Question 4

What is a hysteresis system?

Answer 4

The system’s state is not a strict function of the forcing, but also depends on its history.

Question 5

What are the two types of regimes?

Answer 5

• Always 1 equilibrium state for given forcing
• Sometimes a bistable regime. Which means that when a tipping point is crossed, more energy is required to get it back at its original state.

Question 6

Why do melting times remain highly uncertain?

Answer 6

This is due to complex dynamical processes due to:
- Elevation feedback
- Albedo feedbacks
- Fracture formation
- Basal friction

Question 7

How much of the rainfall is recycled in the Amazon?

Answer 7

25-50% of the Amazon rainfall

Question 8

What are generic early warning signals

Answer 8

Critical slowdown: Slower recovery from small disturbances as a system nears a tipping point.

Increasing variability: Larger fluctuations and instability in the system’s response to disturbances.

Question 9

What does the Gaia hypothesis hold?

Answer 9

It holds that biological processes work to maintain a stable surface climate on Earth to maintain habitability through various negative feedback mechanisms.

Life will result in negative feedback to be able to stay on earth. Similar to homeostasis in living organisms. One of them e.g. is enhanced phytoplankton growth which lead to enhanced aerosols which are important for clood formation, which has a cooling effect.

Question 10

Complete melting takes an enormous amount of energy to take the amount of Greenland ice down. Why?

Answer 10

• Elebation feedbacks
• Albedo feedbacks
• Fracture formation
• Basal friction