5.3 Biodiversity Loss

A silent spring, then and now

In 1962, the American biologist Rachel Carson published Silent Spring, documenting the devastating effects of pesticides on bird populations. The title conjured a nightmare: a spring with no birdsong, because the birds had all been poisoned. The book is widely credited with launching the modern environmental movement and helping to ban the pesticide DDT in many countries.

More than six decades later, the world faces a biodiversity crisis far larger than anything Carson imagined. Scientists estimate that species are going extinct at a rate 100 to 1,000 times higher than the natural background rate. The World Wildlife Fund's Living Planet Report has documented an average 69 percent decline in monitored wildlife populations since 1970. Some researchers argue we are living through the sixth mass extinction in Earth's history -- the first caused not by an asteroid or volcano, but by a single species: humans. And this is not just a problem for wildlife enthusiasts, because healthy ecosystems provide services essential to human survival itself.

The variety of life, and why it matters

Biodiversity -- short for biological diversity -- refers to the variety of life on Earth at all levels, and it operates at three of them. Species diversity is the number and variety of different species in an area; Earth is home to an estimated 8 to 10 million species, of which only about 1.5 million have been formally identified. Genetic diversity is the variation in genes within a single species, and greater genetic diversity makes populations more resilient to disease and environmental change. Ecosystem diversity is the variety of habitats and ecological processes -- rainforests, coral reefs, wetlands, grasslands, deep-sea ecosystems. All three levels are under severe pressure from human activity.

Why should we care? The reasons go well beyond beauty. Biodiversity underpins the ecosystem services humans depend on, including pollination, water purification, soil fertility, climate regulation and natural pest control. Many medicines are derived from natural compounds found in plants, animals, fungi and microorganisms. Crop diversity and the wild relatives of domesticated plants are essential for breeding disease-resistant and climate-adapted food. More diverse ecosystems are more resilient to disturbance and recover better from shocks. And many people and philosophical traditions hold that all species have intrinsic value -- a right to exist regardless of their usefulness to humans, an ethical claim worth taking seriously alongside the practical ones. Coral reefs make the stakes vivid: often called the "rainforests of the sea," they cover less than 1 percent of the ocean floor yet host about 25 percent of all known marine species. The world has already lost roughly half its coral since the 1950s to bleaching from warming seas and to ocean acidification, threatening the food and income of an estimated 500 million people.

The services nature provides, and the crisis of their loss

The concept of ecosystem services -- the benefits humans receive from natural ecosystems -- was popularised by the Millennium Ecosystem Assessment of 2005, which sorted them into four types. Provisioning services are products obtained from ecosystems: food, fresh water, raw materials, and genetic resources and medicines. Regulating services are benefits from ecosystem processes: climate regulation through carbon storage in forests and oceans, water purification by wetlands, flood and erosion control, pollination of crops by bees and birds, and disease regulation. Cultural services are non-material benefits: recreation, tourism, aesthetic and spiritual value, and cultural identity tied to landscapes. And supporting services are the underlying processes that maintain all the others: nutrient cycling, soil formation and photosynthesis.

The scale of value is staggering. Studies estimate the total economic value of global ecosystem services exceeds 100 trillion dollars per year -- more than global GDP. Yet most of these services have no price and are not counted in economic decision-making, which is a key reason they are being degraded and destroyed. The main drivers of biodiversity loss are habitat destruction, climate change, pollution, overexploitation and invasive species. The coral reef crisis shows how interlocked these are: rising temperatures cause coral bleaching, which destroys the habitat supporting a quarter of marine species; ocean acidification from absorbed CO2 weakens coral skeletons; and when reefs die, declines cascade through the marine food web. Major bleaching events in 2016, 2017, 2020 and 2024 devastated reefs worldwide, including parts of the Great Barrier Reef, and many scientists warn that warming above 1.5 degrees could destroy most tropical reefs permanently. The deeper lesson is that the biodiversity crisis is not separate from the climate crisis -- the two are deeply intertwined, and addressing one without the other will not be enough.

In short

The world faces a biodiversity crisis of unprecedented scale, with species going extinct at 100 to 1,000 times the natural rate and monitored wildlife populations down roughly 69 percent since 1970. Biodiversity spans species, genetic and ecosystem diversity, all under severe pressure from habitat destruction, climate change, pollution, overexploitation and invasive species. It matters both practically -- through ecosystem services worth over 100 trillion dollars a year, from pollination to climate regulation -- and ethically, through the intrinsic value of species. Coral reefs show how climate change and biodiversity loss intertwine, as warming-driven bleaching destroys habitat for a quarter of marine species and the livelihoods of 500 million people. The two crises are not separate, and neither can be solved alone.