Loss of biodiversity is the decline in the variety of life on Earth, from the disappearance of entire species to the shrinking of wildlife populations and the degradation of the ecosystems they depend on. The current rate of species extinction is roughly 1,000 times higher than the natural background rate, and monitored vertebrate populations (mammals, birds, amphibians, reptiles, and fish) have dropped by an average of 73% in just 50 years.
What Biodiversity Actually Means
Biodiversity isn’t just a count of how many species exist. It operates on three interconnected levels. The first is genetic diversity: the variation in DNA within a single species that allows populations to adapt to disease, drought, or other pressures. A cheetah population with very little genetic variation, for instance, is far more vulnerable to a single outbreak than one with a wide genetic pool.
The second level is species diversity, which is what most people picture. This is the number and variety of species living in a given area. The third level is ecosystem diversity: the range of habitats, from coral reefs to grasslands to deep-sea vents, each running on different biological processes. When biodiversity is “lost,” the damage can occur at any or all of these levels. A forest might still stand but lose its large predators, which ripples through the food web. A crop species might survive in commercial agriculture but lose the wild relatives whose genes once protected it against new pests.
Five Forces Driving the Decline
The Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services (IPBES) has identified five dominant human-driven forces behind biodiversity loss, ranked by their global impact.
- Land and sea use change. Converting forests, wetlands, and grasslands into farmland, cities, or aquaculture is the single biggest threat. In the United States alone, 82% of imperiled species face pressure from habitat conversion.
- Climate change. Rising temperatures shift the ranges where species can survive, alter migration timing, bleach coral reefs, and intensify droughts and wildfires. Climate change threatens 72% of imperiled U.S. species.
- Invasive species. Non-native plants, animals, and pathogens outcompete or prey on local wildlife. About 52% of U.S. imperiled species are affected.
- Pollution. Pesticides, fertilizer runoff, plastics, and industrial chemicals poison waterways, soil, and air. This factor threatens 34% of U.S. imperiled species.
- Overexploitation. Overfishing, poaching, and unsustainable harvesting of timber and wildlife deplete populations faster than they can recover, affecting 32% of U.S. imperiled species.
These five drivers rarely act alone. A tropical forest fragment surrounded by cropland exposes its remaining wildlife to pesticide drift, invasive predators like feral cats, and warming temperatures all at once. That compounding effect is a major reason populations collapse faster than single-threat models predict.
How Bad the Numbers Are
The World Wildlife Fund’s Living Planet Report 2024 tracked tens of thousands of vertebrate populations across the globe and found an average 73% decline between 1970 and 2020. That doesn’t mean 73% of all animals are gone. It means that, on average, the monitored populations are less than a third the size they were five decades ago. Some regions are hit harder: freshwater species and tropical populations have seen the steepest drops.
Extinction rates paint an even starker picture. The natural “background” rate of extinction, the pace at which species disappeared before human influence became dominant, is estimated at roughly one to five species per year. Current rates are about 1,000 times that baseline, and projections suggest they could reach 10,000 times the background rate if trends continue. Only about 8% of the world’s described species have been formally assessed for extinction risk by the IUCN Red List, so the true scope of loss is almost certainly underestimated.
Why It Matters for Human Health
Biodiversity loss isn’t just an environmental issue. It has direct consequences for medicine and disease. Roughly half of all drugs approved over the past 30 years are derived directly or indirectly from natural products, and in cancer treatment specifically, about 49 of every 100 small-molecule drugs trace back to compounds found in plants, fungi, or marine organisms. Eleven percent of the 252 drugs the World Health Organization considers basic and essential come exclusively from flowering plants. Every species that vanishes takes its unique chemistry with it, potentially including compounds that could have treated antibiotic-resistant infections or emerging cancers.
On the disease side, degraded ecosystems push humans and wildlife into closer contact, raising the odds of viruses jumping from animals to people. Deforestation, wildlife trade, and intensive farming all increase this risk. When complex ecosystems are intact, the many species within them tend to dilute pathogen transmission. Strip that diversity away, and the species that thrive in disturbed habitats, often rodents and bats, are frequently the ones most likely to carry viruses that can infect humans.
The Ripple Effects on Ecosystems
Species don’t exist in isolation. Pollinators like bees and butterflies support the reproduction of roughly 75% of flowering plants, including many food crops. Predators regulate prey populations, preventing overgrazing that can turn forests into barren scrubland. Decomposers break down dead material and recycle nutrients back into the soil. When key species decline or disappear, these processes break down in ways that are often difficult to reverse.
Coral reefs illustrate the cascading effect well. Reefs support about a quarter of all marine species despite covering less than 1% of the ocean floor. When warming waters bleach corals, the fish that depend on them for shelter decline. Coastal communities that rely on those fish for food and income are left vulnerable. The reef itself, weakened without its full community of grazers and cleaners, becomes less resilient to the next bleaching event. Each loss accelerates the next.
Global Efforts to Reverse the Trend
In 2022, nearly 200 countries adopted the Kunming-Montreal Global Biodiversity Framework, the most ambitious international conservation agreement to date. Its headline commitment is the “30 by 30” target: protecting and conserving 30% of the world’s land and 30% of its oceans by 2030. Currently, about 17% of land and roughly 8% of ocean areas have some form of protection, so meeting the target requires a significant expansion in just a few years.
The framework also calls for restoring 30% of degraded ecosystems, reducing pollution from pesticides and excess nutrients, and cutting subsidies that harm biodiversity by at least $500 billion per year. Whether these targets translate into action depends on national follow-through. Previous global biodiversity goals, set in 2010 under the Aichi Targets, were largely missed. The difference this time may come down to monitoring and accountability: the new framework includes a stronger reporting structure designed to track whether countries are actually delivering on their commitments.