EAE 17 - Tipping Point

Question 1

What is the definition of risk?

Answer 1

risk = impact * probability

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Question 2

What is the definition of tipping point?

Answer 2

Tipping points occur when change within a forced system becomes selfperpetuating independent of the original forcing after it passes a critical threshold in the original forcing (the points of no return), and results in a regime shift to a significantly new system state

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Question 3

How do ice ages change?

Answer 3

Records show abrupt transitions between into and out of ice ages, triggered at some critical threshold

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Question 4

What is the ice-albedo positive feedback loop?

3 points.

Answer 4

• Temperature rise
• Arctic sea ice melts
• As reflective ice disappears, darker ocean water absorbs more heat

→ Temperature rise etc

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Question 5

What are the predictions on the ice-albedo feedback?

2 points.

Answer 5

IPCC predicts with high confidence that, by 2100, for sustained global warming of:

• 1.5°C → the Arctic will experience ice-free summers <1% of the time
• 2°C → the Arctic will experience ice-free summers 10-35% of the time (high confidence)

1. The process of sea ice decline under a warming climate is a positive feedback loop
2. But, there’s also a tipping point: global temperature thresholds exist beyond which sea ice is no longer present during summer
3. Such changes in the Arctic constitute a regime shift

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Question 6

What causes tipping between glacials and interglacials?

3 points.

Answer 6

Changes in solar insolation is primary driver

Positive feedbacks contribute to rapid evolution

• Ice-albedo
• Ice-elevation
• Atmospheric greenhouse gas concentrations

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Question 7

What are tipping cascades?

Answer 7

Crossing a threshold in one system may trigger another tipping point.

E.g. loss of Arctic summer sea ice could increase the vulnerability of Greenland to ice loss and sea level rise

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Question 8

What are tipping cascades examples of?

Answer 8

Tipping cascades are examples of deep uncertainty because a lack of data impacts the assessment of probabilities, consequences, and risks

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Question 9

What are the projections of Marine Ice Sheet thinning?

Answer 9

Unstable retreat and thinning of some Antarctic glaciers, and to a lesser extent Greenland outlet glaciers, may be underway.

However, the timescale and future rate of these processes is not well known, casting deep uncertainty on projections of the sea level contributions from the Antarctic Ice Sheet

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Question 10

What are the projections for permatfrost traw?

Answer 10

RCP4.5

• 6-33 Pg soil carbon emission by 2100
• Increase in global temperatures by ~0.10 ± 0.05 °C

RCP8.5

• 23-174 Pg soil carbon emission by 2100
• Increase in global temperatures by ~0.3 ± 0.2 °C

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Question 11

What can we do about permatfrost thaw?

Answer 11

The impact of permafrost thaw (GHG release to the atmosphere) is reversible.

Requires reducing emissions

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Question 12

Coral reef die-off what can we do about it?

4 points.

Answer 12

• Limiting ocean warming by reducing emissions
• Increasing marine protected areas by eliminating fishing, mining, and recreating lead to healthier, more resilient reef
• Assisted gene flow: moving warm-adapted corals to cooler parts of the reef
• Geoengineering strategies: floating sunshields, marine cloud brightening, and water mixing

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Question 13

Describe

Amazon forest dieback

3 points.

Answer 13

• 15200 Pg C in living biomass and soils
• 25% of terrestrial carbon sink (1990-2007)
• Generates about 75% of its own rainfall

Decreasing trend of carbon accumulation, and above ground biomass decline by about 1/3 compared to 1990.

Dieback due to warming climate would self-perpetuate above a 4°C threshold (i.e. RCP8.5 projection at 2100), or a loss of approximately 20% of the current extent.

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Question 14

Will climate change will make the Sahel drier or wetter?

Answer 14

West Africa Monsoon circulation
Seasonal reversal in winds over West Africa linked to ITCZ carbonbrief.

The future projection of the WAM exhibits warming over the entire domain, decreasing precipitation over the southern Sahel, and increase of precipitation over the western Sahara.

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Question 15

What is Marine methane release?

Answer 15

Solid compounds containing methane within crystal structure of water occurring at ocean floor. Possibly holds up to 1400 billion tonnes of carbon.

IPCC reported that release of this methane with warming oceans could constitute a tipping point; however, little evidence that methane bubbles in shallow Arctic are from this source rather than permafrost thaw.

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Question 16

What is Atlantic Meridional Overturning Circulation?

4 points.

Answer 16

• AMOC is large-scale buoyancy-driven system of currents in North Atlantic, responsible for global heat transport.
• AMOC has been weakening since 1950s, due to freshwater flux in the North Atlantic.
• A shut-down might be triggered with 3-4°C warming. This risk is minimised by limiting warming below 2°C.
• (‘Day After Tomorrow?’ film scenario is not likely within hundreds of years)

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