IB ESS HL3.2 Human Impact on BiodiversityHL only~12 min read
Losing Biosphere Integrity
Species are going extinct 100 to 1 000 times faster than the natural background rate. That is not a conservation statistic — it is a planetary boundary, and scientists believe we have already crossed it.
📘 What you need to know
Biosphere integrity is the health and stability of Earth’s biodiversity: ecosystems, habitats, species and genetic diversity.
It is one of the nine planetary boundaries, and scientists believe this boundary has already been crossed.
Species extinction is occurring 100 to 1 000 times faster than the background extinction rate.
This is often called the sixth mass extinction, driven by deforestation, pollution, climate change and habitat destruction.
Losing species can destabilise the whole Earth system, not just individual ecosystems.
Loss of biosphere integrity threatens ecosystem services — clean air, water, food and climate regulation.
What biosphere integrity is
Biosphere integrity refers to the health and stability of the Earth’s biodiversity, including its ecosystems, habitats, species and genetic diversity. It is one of the nine planetary boundaries — thresholds that define a safe operating space for humanity, where crossing a boundary increases the risk of environmental change that could destabilise the Earth system.
The loss of biosphere integrity shows that human activities have caused a rapid decline in biodiversity, pushing species extinction rates beyond the natural threshold. Scientists believe this boundary has already been crossed.
The scale is logarithmic, so the red band sits far to the right. On a linear scale the background rate would be invisible.
This is often called the sixth mass extinction, and is driven by human activities including deforestation, pollution, climate change and habitat destruction. When species are lost it does not just affect individual ecosystems — it can destabilise the whole Earth system, leading to widespread changes affecting climate, air, water and food resources.
Tipping points in the Earth system
Tipping points are critical thresholds where small changes in the environment lead to drastic and irreversible consequences. The loss of key species or ecosystems can create feedback loops that push the Earth system into a new, less stable state. If biodiversity loss continues, it could lead to widespread ecosystem collapse.
The bottom-right box is a positive feedback loop of exactly the kind covered in 1.2: melting reduces reflectivity, which causes more melting.
Tipping point
The consequence
Loss of pollinators
The disappearance of pollinators like bees could disrupt global food production, and would also impact wild flower populations globally
Forest degradation
Reduces carbon storage, accelerating climate change by releasing more carbon dioxide. Large-scale deforestation could push the Amazon past a tipping point where it no longer functions as a rainforest
Loss of phytoplankton
Caused by warming oceans and ocean acidification, this could majorly disrupt the marine food chain, leading to collapse in marine biodiversity and significantly reducing the ocean’s ability to sequester carbon
Arctic sea ice melt
Habitat loss threatens species such as polar bears, and sea-level rise destroys previously biodiverse coastal habitats. Losing ice also reduces Earth’s ability to reflect sunlight, so even more heat is absorbed
There is concern that the loss of species and ecosystems could reach a point where the entire Earth system begins to change in unpredictable ways, affecting climate stability, food security and freshwater availability.
Ecosystem services
Ecosystem services are the benefits humans receive from nature, including clean air, water, food and climate regulation. The loss of biosphere integrity threatens these services, making it harder for ecosystems to provide essential resources for expanding human populations.
This is where 3.2 lands. The sub-topic opened with individual threats to individual species. It ends with a planetary boundary, because those threats aggregate. Each extinction is a local event; a hundredfold increase in the extinction rate is an Earth-system one, and it is the point at which biodiversity loss stops being about wildlife and starts being about climate stability, food security and freshwater.
Memorise one or two clear examples of how biosphere integrity is being eroded and how this has knock-on effects — the Amazon and Arctic sea ice are the two best, because both contain a feedback loop you can explain. Notice this page reuses three ideas from earlier: planetary boundaries from 1.3, tipping points and positive feedback from 1.2, and the sixth mass extinction from 3.1. Examiners reward answers that make those links explicitly.
Worked examples
WE 1
The boundary
Outline what is meant by biosphere integrity and explain why it is a concern. (4 marks)
Step 1: the definition
Biosphere integrity is the health and stability of Earth’s biodiversity, including its ecosystems, habitats, species and genetic diversity.
Step 2: its status as a boundary
It is one of the nine planetary boundaries, thresholds defining a safe operating space for humanity. Crossing one increases the risk of change that could destabilise the Earth system.
Step 3: where we are
Scientists believe this boundary has already been crossed. Species extinction is occurring 100 to 1 000 times faster than the background rate.
Step 4: why it matters
Losing species does not only affect individual ecosystems; it can destabilise the whole Earth system, affecting climate, air, water and food resources.
A crossed planetary boundary, with Earth-system consequencesthe 100 to 1 000 figure is the single most quotable statistic here
WE 2
A feedback loop
Explain how Arctic sea ice melt acts as a tipping point in the Earth system. (4 marks)
Step 1: the initial change
Climate change is causing the melting of Arctic sea ice.
Step 2: the biodiversity impact
This loss of habitat threatens species such as polar bears, and the resulting sea-level rise destroys previously biodiverse coastal habitats.
Step 3: the feedback
Losing ice reduces Earth’s ability to reflect sunlight, so more heat is absorbed, which causes further melting.
Step 4: why this is a tipping point
This is a positive feedback loop, amplifying the original change. Small changes can therefore lead to drastic and irreversible consequences, pushing the Earth system towards a new and less stable state.
Melting causes warming, which causes more meltingclosing the loop is essential — the same rule as in 1.2
WE 3
Consequences for people
Explain how the loss of biosphere integrity threatens human wellbeing. (4 marks)
Step 1: ecosystem services
Ecosystem services are the benefits humans receive from nature, including clean air, water, food and climate regulation. Loss of biosphere integrity threatens these services.
Step 2: food
The disappearance of pollinators such as bees could disrupt global food production, threatening food security.
Step 3: climate
Forest degradation reduces carbon storage, accelerating climate change, and loss of phytoplankton would reduce the ocean’s ability to sequester carbon.
Step 4: the wider risk
The Earth system could begin to change in unpredictable ways, affecting climate stability, food security and freshwater availability, and making it harder for ecosystems to supply resources for expanding human populations.
Biodiversity loss becomes a food, water and climate problemnaming the three named risks — climate, food, freshwater — secures the final mark
💡 Exam tips
Define biosphere integrity across all four levels: ecosystems, habitats, species, genetic diversity.
Say it is one of the nine planetary boundaries and has already been crossed.
Quote the rate: 100 to 1 000 times the background extinction rate.
Prepare two tipping-point examples with the feedback loop explained.
Use the term ecosystem services and name several.
Link explicitly to the sixth mass extinction from 3.1.
⚠ Common mistakes
Treating biosphere integrity as species count alone. It includes genetic diversity and ecosystems.
Saying the boundary is at risk of being crossed. Scientists believe it already has been.
Naming a tipping point without the feedback. The loop is what makes it a tipping point.
Describing biodiversity loss as only an ecological problem. It threatens food, water and climate.
Forgetting phytoplankton. Their loss affects both marine food chains and carbon sequestration.
Assuming these changes are predictable. The syllabus stresses unpredictability.
That completes 3.2 Human Impact on Biodiversity. Nine notes moving outward in scale: individual threats, the status of individual species, shared resources, then at HL the places where loss concentrates, the people who live there, and finally the planetary boundary all of it adds up to. Next comes 3.3, on conservation and regeneration — what can actually be done.
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