Climate Tipping Points (SL IB Environmental Systems & Societies (ESS))

• A tipping point is a critical threshold within a system
  • If a tipping point is reached, any further small change in the system will have significant knock-on effects and cause the system to move away from its average state (away from the equilibrium)
  • In ecosystems and other ecological systems, tipping points are very important as they represent the point beyond which serious, irreversible damage and change to the system can occur
  • Positive feedback loops can push an ecological system towards and past its tipping point, at which point a new equilibrium is likely to be reached
  • Eutrophication is a classic example of an ecological reaching a tipping point and accelerating towards a new state

• Tipping points can be difficult to predict for the following reasons:
  • There are often delays of varying lengths involved in feedback loops, which add to the complexity of modelling systems
  • Not all components or processes within a system will change abruptly at the same time
  • It may be impossible to identify a tipping point until after it has been passed
  • Activities in one part of the globe may lead to a system reaching a tipping point elsewhere on the planet (e.g. the burning of fossil fuels by industrialised countries is leading to global warming, which is pushing the Amazon basin towards a tipping point of desertification) - continued monitoring, research and scientific communication is required to identity these links

(A) The system is subject to a pressure that pushes it towards a tipping point. (B) The system’s tipping point (critical threshold) is reached. Like a ball balancing on a hill, at this stage even a minor push is enough to cross the tipping point, upon which positive feedback loops accelerate the shift (D) into a new state (E). The change to the new state is often irreversible or a high cost is required to return the system back to its previous state, which is illustrated in the figure as a ball being in a deep valley (E) with a long uphill climb back to the previous state (F)

• The melting of polar ice caps and glaciers is just one example of the many ways in which human activities can push the Earth's systems beyond their limits and towards environmental tipping points
• It is important for individuals and governments to take action to reduce greenhouse gas emissions and protect the planet's natural systems

• Any system, ecological, social or economic, has a certain amount of resilience
  • This resilience refers to the system’s ability to maintain stability and avoid tipping points

• Diversity and the size of storages within systems can contribute to their resilience and affect their speed of response to change
  • Systems with higher diversity and larger storages are less likely to reach tipping points
  • For example, highly complex ecosystems like rainforests have high diversity in terms of the complexity of their food webs
  • If a disturbance occurs within one of these food webs, the animals and plants have many different ways to respond to the change, maintaining the stability of the ecosystem
  • Rainforests also contain large storages in the form of long-lived tree species and high numbers of dormant seeds
  • These factors promote a steady-state equilibrium in ecosystems like rainforests
  • In contrast, agricultural crop systems are artificial monocultures meaning they only contain a single species. This low diversity means they have low resilience - if there is a disturbance to the system (e.g. a new crop disease or pest species), the system will not be able to counteract this

A system with high resilience (such as a tropical rainforest) has a greater ability to avoid tipping points than a system with low resilience (such as an agricultural monoculture)

• Humans can affect the resilience of natural systems by reducing the diversity contained within them and the size of their storages
  • Rainforest ecosystems naturally have very high biodiversity
  • When this biodiversity is reduced, through the hunting of species to extinction or the destruction of habitat through deforestation, the resilience of the rainforest ecosystem in reduced - it becomes increasingly vulnerable to further disturbances
  • Natural grasslands have high resilience, due to large storages of seeds, nutrients and root systems underground, allowing them to recover quickly after a disturbance such as a fire (especially if they contain a diversity of grassland species, including some which are adapted to regenerate quickly after fires)
  • However, when humans convert natural grasslands to agricultural crops, the lack of diversity and storages (e.g. no underground seed reserves) results in a system that has low resilience to disturbances such as fires