6.2D Tipping cascades (HL) Notes

1. A tipping point is the critical threshold at which a small change causes a large, abrupt, and potentially irreversible shift in a component of the Earth system.
2. Individual climate tipping points can be abiotic, biotic, or combined interactions involving both.
3. Examples include: ice sheet collapse, permafrost thaw, coral bleaching, AMOC disruption, rainforest dieback, and phytoplankton collapse.
4. As global warming intensifies, multiple tipping points may be activated within the same time window, increasing the risk of cascading failures.

Why Tipping Cascades Make Climate Predictions Uncertain

1. Tipping elements are interconnected across atmosphere, ocean, cryosphere, and biosphere.
2. Changes in one region (e.g., Greenland meltwater) modify processes in distant systems (e.g., AMOC slowdown).
3. Interactions are nonlinear.
4. Small disturbances can produce disproportionately large responses.
5. Cascades may activate at lower global warming levels than previously expected.
6. Climate system feedbacks amplify effects, making model predictions highly uncertain.

Key Examples of Climate Tipping Points

1. Greenland Ice Sheet Melt: Loss of ice reduces the mass of land ice and increases runoff of freshwater into the North Atlantic.
2. West Antarctic Ice Sheet Collapse: Melting reduces ice mass and contributes to rapid rises in sea level.
3. Arctic Sea Ice Loss: Removal of reflective ice exposes darker ocean surfaces that absorb more heat, causing additional warming.
4. Permafrost Thaw: Thawing soils release methane and carbon dioxide, which intensify global temperature rise.
5. Amazon Rainforest Dieback: Loss of forest cover reduces rainfall and evapotranspiration, making it harder for the forest to regenerate.
6. Boreal Forest Decline: Increased heat, pests and fire frequency reduce forest stability.
7. Coral Reef Collapse: Warming and acidified waters cause bleaching and reduce biodiversity in marine ecosystems.
8. Atlantic Meridional Overturning Circulation (AMOC) Slowdown: Altered salinity and temperature patterns weaken the circulation of warm and cold water in the Atlantic Ocean.

How Tipping Cascades Develop

1. Interconnected Feedback Loops

1. One tipping point changes a physical or biological condition that another tipping point depends on.
2. The melting of the Greenland Ice Sheet reduces salinity in the North Atlantic.
3. Reduced salinity decreases the density of seawater.
4. Less dense water sinks more slowly, which weakens deepwater formation.
5. Weakening deepwater formation reduces the strength of the AMOC.
6. A weakened AMOC alters heat transport across the globe, which affects rainfall patterns.

2. Positive Feedbacks Accelerate System Change

1. Once a tipping point is crossed, reinforcing feedback loops strengthen the change.
2. In the Arctic, loss of sea ice decreases albedo, causing greater absorption of sunlight.
3. Greater heat absorption increases ocean temperatures and creates faster ice melt.
4. Permafrost thaw releases methane that intensifies warming and leads to even more thaw.

3. Cascading Consequences

1. When multiple tipping points interact, the combined effect is far greater than each tipping point acting alone.
2. Cascades produce rapid changes such as faster sea-level rise, widespread droughts, more extreme weather events and ecosystem collapse.

4. Irreversibility and New Equilibrium States

1. Many tipping cascades cannot be reversed once they have begun.
2. Ice sheets may not recover once they lose structural integrity.
3. Rainforests may not regenerate once they transition to savannah conditions.
4. Oceans may remain stratified or circulation patterns may remain disrupted for centuries.
5. After a tipping cascade, the climate system settles into a new equilibrium with different temperature, precipitation and carbon-storage characteristics.
6. These new states are often warmer, less stable and less biodiverse.

Types of Tipping Points

Biotic Tipping Points (Organism-Driven)

1. The Amazon rainforest (biotic tipping point) and Arctic permafrost (abiotic tipping point) could interact if increased deforestation releases carbon.
2. This carbon further accelerates global warming, leading to a feedback loop where both ecosystems shift beyond their tipping points.

Abiotic Tipping Points (Physical-Climate Driven)

1. Ocean circulation changes (e.g., AMOC slowdown) could interact with Arctic ice melt and permafrost thawing.
2. As the AMOC weakens, colder water could reduce the volume of ice in the Arctic, accelerating Arctic melt and releasing more methane from permafrost.

Biotic/Abiotic Combination Tipping Points

1. The Amazon rainforest collapse and increased carbon emissions from deforestation could exacerbate global warming, causing regional climate changes (e.g., droughts in Africa).
2. These changes could further impact water resources and agriculture, ultimately pushing additional biomes (e.g., savannas) past their tipping points.

Social Tipping Points

1. Human behaviour can also shift suddenly and create positive or negative cascades in climate outcomes.
2. Stabilizing social tipping points include:
   1. removal of fossil fuel subsidies
   2. rapid adoption of renewable energy
   3. widespread climate education
   4. large-scale use of public transportation
   5. carbon-neutral urban planning
3. Positive social tipping cascades can counteract environmental tipping cascades.

Why Tipping Cascades Increase Climate Uncertainty

1. Climate models struggle to determine the precise thresholds at which tipping points occur.
2. Small uncertainties in one tipping element cause larger uncertainties across linked systems.
3. Interactions between biotic and abiotic systems are complex and not fully understood.
4. Cascades may unfold at different speeds, which makes predictions difficult.
5. Some tipping points may occur earlier than expected because of interactions between systems.