Module 3 / Lesson 8.3

Climate Change as Existential Risk

2 min read

What does Ord say about climate change as a possible source of existential risk?

The Spectrum of Risk

- Learning:
  - Read Ord The Precipice, pp. 102–113 on existential risk from climate change.
  - Read Ord The Precipice, pp. 113-119 on existential risk from other environmental damage
  - Focus closely on Page 103-5, where Ord categorizes the different ways climate change threatens humanity.
  - Look at our list of ways to think about the harm of climate change below, separating harm from climate change into three categories.
- Reflection:
  - Looking at the list below of ways to think about how climate change might be harmful, most media coverage focuses on Category A (harm on average, expected harm). Ord argues that as "Existential Risk scholars," we must also consider on B and C below. Why is this distinction important for where we spend our money?

Three Ways Climate Change Matters

Ord identifies three reasons to worry about climate change:

A. Climate Change is Expected to be Harmful:
The standard view. Climate change is expected to cause a warming of 3 degrees centigrade on average (assuming current policy continues), causing significant economic damage, displacement of millions, and loss of biodiversity. This level of warming would be harmful, but would not be an existential risk because humanity survives.

B. Climate Change as Direct Existential Risk. Possibility That Climate Change Could be Far Worse Than Expected, Creating an Unlivable Earth (Direct Extinction):
The possibility that climate change could be far worse than the expected outcome outlined in A. This could happen if feedback loops push the planet into a "runaway greenhouse" state (like Venus), so that the earth becomes too hot to live on. (See Ord's description of this possibility on p. 103-104). How likely is it that climate change is far worse than expected? Why? (See Section 8.2 for reasons to be uncertain about climate change.) Why might climate change be much worse than expected:

Runaway Greenhouse Effect:
- Oceans boil and Earth becomes more Venus.
- Ord (p. 104): This is considered very unlikely based on physics.
Moist Greenhouse Effect:
- A scenario with ~40°C warming. Oceans don't boil, but it is catastrophic per Ord, p. 104.
- Context: Historical records show only 9–14°C warming variance per Ord, p. 105.
Other Feedback Risks:
- Permafrost & Methane (p. 106): Melting releases stored carbon, causing more heating.
- Climate Sensitivity (p. 108): We usually estimate 1.5–4.5°C warming per doubling of CO2. But it could be 1.5–9°C. If policy fails and sensitivity is high, we could hit 13°C warming by 2300 (p. 110).

C. Climate Change as Indirect Source of Existential Risk. Possibility That Climate Change Could Trigger Other Existential Risks (Indirect Extinction):
The possibility that climate change could trigger OTHER existential risks. For example, climate change could make resources scarce, triggering a Nuclear War. Or perhaps climate change could cause economic collapse preventing us from defending against a pandemic. (See Ord's description of this possibility on p. 110-111).

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