Critical Climate Thresholds & Tipping Points (HL) (DP IB Environmental Systems & Societies (ESS)) : Revision Note

Critical Climate Thresholds & Tipping Points

• Climate thresholds are points at which small changes in climate conditions can lead to significant shifts in the Earth’s systems

• Once a threshold is crossed, a new climate equilibrium may be established

• These shifts can be rapid and difficult to reverse

• Critical thresholds are often referred to as 'tipping points'

Global tipping points

• Global tipping points occur when climate changes reach critical levels on a global scale

  • Reaching a global tipping point can lead to unpredictable and potentially catastrophic impacts

  • Positive feedback loops are key in tipping points

    • These loops can amplify changes

    • This can push the climate towards a new, often more extreme state

Examples of global tipping points

• Antarctic ice sheet melting:

  • Melting ice reduces the albedo (reflectivity) of the Earth’s surface

  • This causes more heat absorption

  • This leads to further melting, creating a positive feedback loop

  • Antarctic ice loss contributes to rising sea levels worldwide

  • Sea level rise endangers many coastal ecosystems and human populations

• Atlantic thermohaline circulation (AMOC) slowing:

  • AMOC is a major ocean current that regulates global climate

  • Melting Greenland ice releases fresh water into the North Atlantic

  • This reduces ocean salinity

  • This decreases water density, which weakens the sinking motion that drives the AMOC

  • This slowing disrupts the global flow of heat and nutrients

  • This affects climate patterns, especially in Europe and North America, potentially leading to harsher winters

• Amazon Rainforest-Cerrado transition (CAT):

  • Deforestation and warming threaten the stability of the Amazon rainforest

  • Loss of forest cover is shifting the ecosystem from rainforest to a drier, more savannah-like ecosystem similar to the Cerrado

  • This is reducing carbon storage

  • This is contributing to more greenhouse gases in the atmosphere, accelerating global climate change

Local tipping points

• Local systems, like specific ecosystems or regions, also have their own climate-related thresholds

  • If these thresholds are crossed, significant and rapid changes can occur within the local environment

Example of local tipping point

• Coral reef bleaching:

  • Increased ocean temperatures can cause coral bleaching

  • Without their symbiotic algae, corals struggle to survive

  • This leads to widespread reef death if temperatures do not stabilise

  • Coral reefs support diverse marine life, so their loss can significantly reduce local marine biodiversity

Tipping cascades

• Individual tipping points within the climate system can interact

  • This can create 'tipping cascades'

  • When one tipping point is crossed, it can make other tipping points more likely to be reached

  • These interactions increase the uncertainty in predicting the pace and scale of climate change

Example of a tipping cascade

1. Increased temperatures:

   • Rising temperatures melt Arctic ice, reducing sunlight reflection and causing further warming and ice loss

   • This leads to...?

2. Permafrost thawing:

   • Warmer Arctic temperatures thaw permafrost, releasing greenhouse gases like methane and carbon dioxide, which further accelerates warming

   • This leads to...?

3. Greenland ice sheet melting:

   • Warming leads to melting of Greenland’s ice, adding freshwater to the North Atlantic and disrupting the Atlantic thermohaline circulation

   • This leads to...?

4. Global climate impact:

   • These combined tipping points—Arctic ice melt, permafrost thaw, and AMOC disruption—create a tipping cascade that results in:

     • Increased global temperatures

     • Raised sea levels

     • Disrupted global weather patterns

Biotic and abiotic tipping points

• Individual tipping points can be biotic, abiotic or a combination of biotic and abiotic factors

• Biotic tipping points:

  • Involve living organisms, such as forests, reefs, and biodiversity loss

  • E.g. widespread tree loss in rainforests can change local climate and disrupt water cycles

• Abiotic tipping points:

  • Involve non-living components of the Earth, like ice sheets, oceans, and atmosphere

  • E.g. melting of permafrost releases greenhouse gases (methane and CO₂) into the atmosphere, increasing global warming