Syllabus Edition
First teaching 2015
Last exams 2025
Climate Tipping Points (DP IB Environmental Systems & Societies (ESS))
Revision Note
Written by: Alistair Marjot
Reviewed by: Bridgette Barrett
Tipping Points
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)
Worked Example
Evaluate the possible consequences of environmental tipping points, using the melting of polar ice caps and glaciers as an example.
Answer
The consequences of environmental tipping points can be severe and long-lasting, with effects that extend beyond the immediate environment. One such example is the melting of polar ice caps and glaciers, which can have the following consequences:
Rising Sea Levels:
As polar ice caps and glaciers melt, the water they release adds to the volume of the ocean. This can lead to rising sea levels, which can inundate low-lying areas and cause flooding, erosion, and damage to infrastructure.
Changes in Ocean Currents:
The melting of polar ice caps and glaciers can alter the salinity and temperature of the ocean, which can affect ocean currents. Changes in ocean currents can impact global weather patterns and have cascading effects on ecosystems.
Loss of Biodiversity:
Polar regions are home to a diverse range of species, many of which are adapted to the extreme conditions found there. The loss of polar ice caps and glaciers can lead to the loss of habitat and food sources, leading to declines in biodiversity.
Release of Greenhouse Gases:
Melting permafrost, which is soil that has been frozen for long periods, can release large amounts of methane and carbon dioxide, which are both potent greenhouse gases. This can contribute to climate change and lead to further melting of polar ice caps and glaciers.
Changes in Global Temperatures:
The melting of polar ice caps and glaciers can change the reflective properties of the Earth's surface. This can result in more sunlight being absorbed, leading to an increase in global temperatures and further melting of ice.
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
Resilience
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
Worked Example
Giving a specific example of each, discuss an ecological system with high resilience and an ecological system with low resilience.
Answer
Mangrove forests are coastal ecosystems found in tropical and subtropical regions. They are an example of an ecological system with high resilience. This is due to several factors:
Adaptability:
Mangroves have evolved to survive in harsh coastal conditions, including saltwater inundation due to tidal flooding. They are also able to withstand and adapt to changing environmental conditions, such as sea-level rise and storm surges.
Self-regeneration:
Mangroves have a unique ability to self-regenerate through the production of propagules, which can sprout into new trees. This allows them to recover quickly from disturbances such as storms, hurricanes, and tsunamis.
Biodiversity:
Mangroves support high levels of biodiversity, with many species of plants and animals adapted to their unique ecosystem. This biodiversity provides a buffer against disturbances, as it allows for the maintenance of ecological processes and the provision of ecosystem services.
Nutrient Cycling:
Mangroves are efficient at cycling nutrients, such as nitrogen and phosphorus, within their ecosystem. This helps to maintain soil fertility and supports the growth of mangrove trees and other vegetation.
Coral reefs are an example of an ecological system with low resilience. This is due to several factors:
Multiple Simultaneous Stressors:
Coral reefs are under threat from a range of human activities, including overfishing, pollution and coastal development.
Rising Sea Temperatures:
Coral reefs are particularly vulnerable to climate change, which is causing ocean temperatures to rise and making the water more acidic. This can cause coral bleaching, which can lead to mass coral mortality and the degradation of the entire reef ecosystem.
Slow Recovery Rate:
Once coral reefs have been damaged, their recovery can be slow and difficult. This is because corals grow slowly and are vulnerable to further damage while they are recovering. If the disturbances continue, the reef may reach a tipping point beyond which it cannot recover.
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