Key Takeaway
Biodiversity is the variety of all life on Earth, operating across three interconnected levels: genetic, species, and ecosystem diversity. Scientists estimate 8.7 million eukaryotic species exist globally, yet only 13% have been formally described. The current extinction rate is 100–1,000 times the natural background rate, making biodiversity loss one of the defining crises of our time.
Biodiversity — short for biological diversity — is the total variety of life on Earth. It encompasses every living organism, from soil bacteria and deep-sea fungi to blue whales and ancient redwood trees, along with all the ecosystems and ecological processes that connect them.
The term was first coined in 1985 by biologist Walter G. Rosen and gained international recognition through the Convention on Biological Diversity (CBD) at the 1992 Rio Earth Summit. The CBD defines biodiversity as "the variability among living organisms from all sources including terrestrial, marine and other aquatic ecosystems and the ecological complexes of which they are part."
In practical terms, biodiversity is what makes ecosystems function. It underpins the air we breathe, the food we eat, the water we drink, and the medicines that keep us alive. According to the Dasgupta Review commissioned by the UK Government, global ecosystem services are valued at USD 125–145 trillion annually — more than the combined GDP of every nation on Earth.
Biodiversity operates across three nested, interdependent levels. Each level matters — and loss at any level cascades upward, weakening the whole system.
Genetic diversity is variation in genes within a single species. It is the raw material for evolution and adaptation. When a population has high genetic diversity, it can better withstand disease, climate stress, and habitat change. For example, wild wheat relatives in the Fertile Crescent contain genetic traits for drought tolerance that plant breeders now use to develop climate-resilient crop varieties. Conversely, low genetic diversity makes populations vulnerable — the Irish Potato Famine of the 1840s resulted from reliance on a genetically uniform potato crop.
Species diversity is the variety and abundance of different species in a given area. It has two components: species richness (the raw count of species present) and species evenness (how equitably those species are distributed). A tropical rainforest with 300 plant species per square metre has far greater species diversity than a temperate grassland with 10–50 species, but both play essential roles in their respective biomes.
Ecosystem diversity is the variety of ecosystems — forests, wetlands, coral reefs, grasslands, deserts — and the ecological processes within them. Different ecosystems provide distinct services: forests store carbon, wetlands filter water, coral reefs protect coastlines. According to IPBES, loss at lower levels cascades upward. Genetic diversity loss narrows species' adaptive capacity; species loss reduces ecosystem function; ecosystem loss reduces global biospheric stability.
| Level | What It Measures | Example | Consequence of Loss |
|---|---|---|---|
| Genetic | Variation in genes within a species | Drought-resistant wild wheat genes | Reduced adaptation to disease and climate stress |
| Species | Number and abundance of different species | Coral reefs support 25% of marine species on less than 1% of ocean floor | Pollinator loss leads to crop failure; predator removal triggers prey explosions |
| Ecosystem | Variety of ecosystems and ecological processes | Freshwater systems cover 1% of Earth but support 10% of known species | Loss of carbon sequestration, altered water cycles, biome collapse |
Source: Convention on Biological Diversity 1992, IPBES Global Assessment 2019
The short answer: we do not know. The best scientific estimate puts the total number of eukaryotic species (organisms with complex cells) at approximately 8.7 million, according to a landmark study published in PLoS Biology by Mora et al. (2011). Of these, roughly 6.5 million live on land and 2.2 million in the ocean.
The sobering reality is that only about 13% of these species have been formally described by science. Insects are the most dramatically undercharacterised group: an estimated 5–10 million species exist, yet only around 1 million have been catalogued. Fungi are even more mysterious — scientists have described roughly 150,000 species from an estimated 2.2–3.8 million, meaning we have identified as few as 4–7% of all fungal species.
These knowledge gaps matter because we cannot protect what we have not identified. Every year, researchers describe thousands of new species, yet extinctions are outpacing discoveries. The IUCN Red List (2024) reveals that among the species we have assessed, amphibians face the highest threat levels at 27.3%, followed by plants at 25.5% and mammals at 19.3%.
8.7M
Estimated Species
Eukaryotic species globally
13%
Formally Described
Science has named ~1.2M species
1M+
Threatened Species
At risk of extinction (IPBES 2019)
68%
Vertebrate Decline
Average population loss 1970–2020
Sources: Mora et al. PLoS Biology 2011, IPBES Global Assessment 2019, WWF Living Planet Report 2024
No single metric captures every dimension of biodiversity. Researchers and conservation practitioners use a suite of complementary indices, each designed to answer a different question about the state of life in a given area.
Species Richness (S) is the simplest measure — a raw count of species present. It is easy to understand and communicate, making it useful for monitoring biodiversity hotspots. However, it ignores abundance: a site dominated by one species with a few rare others scores the same richness as a site with perfectly balanced populations.
Simpson's Diversity Index (D = 1 − Σpi²) addresses this by weighting results towards the most abundant species. A score closer to 1 indicates greater diversity. It is widely used in marine biodiversity assessment, including monitoring by the OSPAR Commission for European seas.
Shannon Diversity Index (H = −Σpi × ln pi) gives more weight to rare species. Values typically range from 1.5 to 3.5 for natural communities. It is particularly useful when the conservation goal is protecting rare or endangered species rather than maintaining overall ecosystem stability.
Environmental DNA (eDNA) is a transformative technology gaining rapid adoption. Scientists extract and sequence DNA fragments from environmental samples — soil, water, even air — without needing to catch or observe organisms directly. This non-invasive method detects rare, nocturnal, and cryptic species that traditional surveys miss. The UK's Environment Agency now uses eDNA monitoring for otter detection in rivers, and pan-European butterfly monitoring networks are rolling out DNA metabarcoding to automate species identification.
At a global scale, the Living Planet Index tracks population trends across thousands of vertebrate species, producing the headline statistic that vertebrate populations declined by an average of 68% between 1970 and 2020. The Biodiversity Intactness Index compares current ecological integrity against natural baselines, currently sitting at around 88% globally — meaning we have lost roughly 12% of our planet's biological completeness since pre-industrial times.
The IPBES Global Assessment (2019) identified five direct drivers of biodiversity loss, ranked by their impact on terrestrial and freshwater ecosystems. These drivers rarely act in isolation — their combined effects are often more devastating than any single threat.
Land and Sea Use Change
The single greatest driver. Habitat conversion for agriculture, urban expansion, and infrastructure has destroyed or degraded natural habitats across every continent. Tropical forests, which harbour roughly 50% of all species, have lost more than half their original extent.
Climate Change
Rising temperatures, shifting precipitation patterns, and extreme weather events force species to move, adapt, or perish. Coral bleaching events — driven by ocean warming — now threaten more than 50% of the world's reef systems.
Pollution
Chemical pollutants, plastic waste, nutrient runoff, and light and noise pollution contaminate ecosystems worldwide. Research published in PLoS ONE found a 75% decline in flying insect biomass across temperate protected areas since 1990 — a collapse with direct consequences for pollination and food webs.
Overexploitation
Overfishing, unsustainable hunting, and excessive resource extraction deplete populations faster than they can recover. Approximately 90% of large commercial fish stocks are now fully fished or overfished, according to the FAO.
Invasive Alien Species
Non-native species introduced to new environments can devastate local ecosystems. Island species are particularly vulnerable — invasive rats, cats, and stoats have driven hundreds of island bird species to extinction. The global economic cost of invasive species damage runs to hundreds of billions annually.
The most significant global commitment is the Kunming-Montreal Global Biodiversity Framework (KMGBF), adopted in December 2022 at COP15. Its headline target — known as 30×30 — aims to protect 30% of the world's land and ocean by 2030.
Progress has been uneven. As of 2024, approximately 17% of land and 8% of ocean areas are designated as protected. Reaching the 30% target by 2030 would require annual increases of 1.5–2% — roughly three to four times the current rate of expansion. The adoption of the High Seas Treaty in 2023 was a landmark step, enabling marine protected areas beyond national jurisdiction for the first time.
Quality also matters. Research by UNEP-WCMC suggests that 40–50% of existing protected areas lack adequate management funding, functioning as "paper parks" with legal designation but little practical enforcement.
The KMGBF also commits nations to restoring 30% of degraded ecosystems by 2030, reducing pollution, eliminating plastic waste, and closing the biodiversity financing gap — estimated at USD 130–250 billion annually between what is currently spent and what is needed. In the EU, the Nature Restoration Law adopted in 2024 sets legally binding targets to restore 20% of degraded ecosystems by 2030 and 90% by 2050.
The connection between biodiversity and human wellbeing is far more direct than most people realise. Around 25% of modern pharmaceutical compounds originate from plants, and 70% of cancer drugs have natural product origins. Paclitaxel (Taxol), one of the most widely used anti-cancer treatments, comes from the Pacific yew tree. Artemisinin, the frontline antimalarial drug that earned a Nobel Prize in 2015, derives from Artemisia annua, a plant used in Chinese traditional medicine for centuries.
Biodiversity loss also increases pandemic risk. According to the UN Environment Programme, 75% of emerging infectious diseases are zoonotic — transmitted from animals to humans. When habitat destruction fragments wildlife populations, it increases the edges of contact between humans and wildlife, creating more opportunities for pathogen spillover. Diverse wildlife communities dilute pathogen prevalence; habitat loss concentrates generalist species that amplify transmission risk.
There is also growing evidence for a direct link between biodiversity and mental health. A landmark study published in Scientific Reports found that spending at least 120 minutes per week in nature is associated with significantly better health and wellbeing. UK NHS trusts have begun piloting "nature prescription" programmes, directing patients to biodiversity-rich green spaces as part of treatment plans for anxiety and depression.
The Hidden Cost of Extinction
Common assumption: Losing obscure species like insects or fungi does not affect us directly.
The reality: An estimated 600,000+ species may contain bioactive compounds useful in medicine — yet only about 5% have been screened. Penicillin came from a mould. The next breakthrough antibiotic, cancer treatment, or antiviral could be in a species we have not yet discovered. Every extinction permanently closes a door to potential human benefit.
The numbers paint a stark picture. The WWF Living Planet Report 2024 documented an average 68% decline in monitored vertebrate populations between 1970 and 2020. Freshwater species have been hit hardest, with an 83% average population decline — a devastating loss given that freshwater systems occupy less than 1% of Earth's surface yet support approximately 10% of all known species.
The current extinction rate is estimated at 100–1,000 times the natural background rate. Before human influence, the fossil record suggests 0.1–1 species per million went extinct each year. Today, that figure is at least 10–100 species per million per year — and the true rate is likely higher, given that millions of species remain undiscovered.
There are 36 recognised biodiversity hotspots worldwide — regions containing at least 1,500 endemic plant species that have lost 70% or more of their original habitat. The Tropical Andes, Atlantic Forest, and Madagascar rank among the most species-rich and most threatened. Most hotspots retain less than 25% of their original habitat; several retain less than 10%.
The economic consequences are immense. The Dasgupta Review calculated that continuing on the current trajectory of biodiversity loss would cost USD 5–10 trillion annually by 2050. Investing in conservation and restoration — at an estimated USD 300–500 billion per year — would yield a net benefit of USD 10–20 trillion over 30 years, making it one of the highest-return investments available to humanity.
For a detailed look at how biodiversity loss is affecting the UK specifically, read our complete guide to biodiversity loss and threats.
Explore UK Biodiversity in Depth
Learn about the species, habitats, and conservation efforts shaping Britain's natural heritage.
Read the UK Biodiversity GuideWhat is a simple definition of biodiversity?
Biodiversity is the variety of all life on Earth. It includes every living organism — from microscopic bacteria to the largest whales — along with the genetic differences within species, the range of species in any given area, and the variety of ecosystems they form. The term comes from "biological diversity" and was first popularised in the mid-1980s.
Why is biodiversity important for humans?
Biodiversity directly supports human survival and wellbeing. It provides food, clean water, medicines (25% of pharmaceuticals come from plants), climate regulation, flood protection, and pollination services worth tens of billions annually. It also reduces pandemic risk — diverse ecosystems dilute pathogen prevalence — and supports mental health through access to biodiverse natural spaces.
What are the three types of biodiversity?
The three levels are genetic diversity (variation in genes within a species), species diversity (the number and abundance of different species in an area), and ecosystem diversity (the variety of ecosystems such as forests, wetlands, and coral reefs). These levels are interconnected — loss at one level weakens the others.
How fast are species going extinct?
The current extinction rate is estimated at 100 to 1,000 times the natural background rate. The IPBES Global Assessment estimates that approximately 1 million animal and plant species are currently threatened with extinction. Around 900 species have been documented as extinct since 1500, but the true figure is certainly higher because millions of species remain undiscovered.
What is the 30x30 target?
The 30x30 target is the centrepiece of the Kunming-Montreal Global Biodiversity Framework adopted in 2022. It commits nations to protecting 30% of the world's land and ocean by 2030. As of 2024, approximately 17% of land and 8% of ocean are protected, meaning significant acceleration is needed to meet the target.
How can I help protect biodiversity?
Individual actions that make a measurable difference include: supporting local conservation organisations, choosing sustainably sourced food and products, reducing pesticide use in gardens, creating wildlife-friendly habitats (even a small pond supports dozens of species), reducing consumption of single-use plastics, and advocating for stronger environmental policies. For UK-specific guidance, see our guide to protecting biodiversity.
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Read the Conservation GuideClwyd Probert
Founder, Pixcellence
Clwyd founded Pixcellence as a conservation and biodiversity resource, combining wildlife photography with education to raise awareness of the natural world. This guide draws on the latest research from IPBES, WWF, and the Convention on Biological Diversity.