Biodiversity loss occurs when species vanish completely from Earth (called extinction) or when species numbers drop in a particular area. This loss means there is less variety of living things in a place. The decrease can be temporary or permanent. If the cause of the loss can be fixed, such as by restoring ecosystems, the loss may be temporary. If the damage cannot be fixed, the loss is permanent. Most biodiversity loss is caused by human activities that push Earth’s natural limits too far. These activities include destroying habitats (like cutting down forests) and using land in ways that harm nature (like farming only one type of crop). Other problems include pollution, overusing natural resources, introducing non-native species, and climate change.

Many scientists and reports, such as the Global Assessment Report on Biodiversity and Ecosystem Services, say that growing human populations lead to overpopulation and overuse of resources. Others argue that habitat loss is mainly caused by producing goods for trade, not population size. They say wealth differences between and within countries are more important. In all cases, human actions are the main cause of current biodiversity loss.

Climate change also threatens biodiversity. For example, coral reefs—areas with high species diversity—may disappear by 2100 if global warming continues. Rising temperatures may also increase wildfires. However, habitat destruction, often for farming, is currently the bigger cause of biodiversity loss than climate change. Invasive species and other disturbances have become more common in forests over recent decades. These are often linked to climate change and harm forest ecosystems.

Environmental groups have worked for many years to stop biodiversity loss. Today, many global policies include actions to protect biodiversity. For example, the UN Convention on Biological Diversity aims to prevent loss and protect natural areas. However, a 2020 report by the United Nations Environment Programme found that most efforts have not met their goals. For instance, of 20 biodiversity targets set in 2010, only six were "partially achieved" by 2020.

This ongoing extinction event is also called the Holocene extinction or the sixth mass extinction.

Global estimates across all species

Scientists estimate that the current rate of biodiversity loss is 100 to 1,000 times faster than the natural extinction rate. This is the fastest rate of loss in human history and is expected to increase in the future. Rapid extinction rates among animals such as mammals, birds, reptiles, amphibians, and fish have led scientists to declare a biodiversity crisis in both land and ocean ecosystems.

In 2006, more species were officially listed as rare, endangered, or threatened. Scientists also estimate that millions of other species not yet identified are at risk. Evidence shows that unlisted species face a higher risk of extinction.

Deforestation is a major cause of biodiversity loss. Over half of the world’s biodiversity lives in tropical rainforests. Areas with very high biodiversity loss are called biodiversity hotspots. From 1988 to 2006, the number of hotspots increased from 10 to 34. Of these 34 hotspots, 16 are in tropical regions. In 2006, researchers found that only 2.3% of the Earth’s surface includes hotspots. However, these hotspots are home to about 50% of all vascular plant species.

In 2021, about 28% of the 134,400 species studied using the IUCN Red List criteria were listed as threatened with extinction. This means 37,400 species are at risk, compared to 16,119 in 2006. A 2022 study of over 3,000 experts suggested that global biodiversity loss and its effects might be worse than previously believed. They estimated that about 30% of species have been threatened or gone extinct since 1500.

A 2023 study found that of 70,000 species studied, about 48% have decreasing populations due to human activities. Only 3% show increasing populations.

Methods to quantify loss

Biologists describe biodiversity as the "entire collection of genes, species, and ecosystems in a specific area." To measure how quickly biodiversity is decreasing in a location, scientists track the number of species present and how that number changes over time. In ecology, local abundance refers to how many members of a species are found in a particular ecosystem. This is often measured by counting how many individuals are found in each sample. The comparison of how many individuals one species has compared to one or more other species in the same ecosystem is called relative species abundance. Both of these measurements are important for calculating biodiversity.

There are many types of biodiversity indexes. These indexes look at different areas and time periods. Biodiversity includes several categories and levels, such as phylogenetic diversity, species diversity, genetic diversity, and nucleotide diversity.

The topic of whether biodiversity is decreasing in limited areas is often discussed and debated.

Observations by type of life

An October 2020 study by Swiss Re found that one-fifth of all countries are at risk of ecosystem collapse due to human-caused habitat destruction and the loss of wildlife. If these losses are not reversed, total ecosystem collapse could occur.

In 2022, the World Wildlife Fund reported that the average population of 4,400 animal species worldwide declined by 68% between 1970 and 2016. This decline included nearly 21,000 monitored populations.

Insects are the most numerous and widespread group in the animal kingdom, making up to 90% of all animal species. Reports from the 2010s showed widespread declines in insect populations across many groups. These findings surprised many people, even though earlier studies had already noted declines in pollinator species. Some people remember seeing more insects in the past, such as when insects hit car windshields. Causes of insect declines include habitat destruction, intensive farming, pesticide use, introduced species, and, in some areas, climate change. Light pollution is also being studied as a possible cause for some insect declines.

Most insect declines involve fewer numbers of insects, though some species are disappearing completely. Declines are not the same everywhere. In some places, insect populations have increased, and some types of insects are growing more common globally. Bees, butterflies, moths, beetles, dragonflies, and damselflies are among the most affected groups. Other insect groups have received less research, and data from earlier years are often missing. Global studies estimate that 10% to 40% of insect species may be at risk of extinction, though these estimates are debated.

Scientists studied earthworms in long-term agricultural experiments and found that their numbers dropped by 50% to 100% (an average of 83%). This loss matches or exceeds declines seen in other animal groups. Earthworms help with soil health, water movement, and balancing greenhouse gases. Five main reasons for earthworm declines include soil degradation, climate change, pollution, overuse of soil, and invasive species. Practices like farming and land use harm the soil and plant roots that earthworms rely on, disrupting important cycles like carbon and nitrogen.

Only about half of all earthworm species have been identified, and more research is needed. Sustainable farming methods, such as reducing soil disturbance, could help protect earthworm diversity. The Convention on Biological Diversity is working to restore and protect earthworm species.

Since the 1980s, amphibian populations worldwide have declined, with some species disappearing completely in certain areas. This is one of the most serious threats to global biodiversity. Possible causes include habitat loss, disease, pollution, pesticides, invasive species, and increased ultraviolet-B radiation. However, many reasons for these declines are still not fully understood.

Studies suggest that the current extinction rate for amphibians could be 211 times higher than the natural background rate. This number rises to 25,000–45,000 times if endangered species are included.

Wild mammal populations have declined for over 50,000 years, as human and livestock populations grew. Today, the total weight of wild mammals on land is about seven times lower than it was in the past, and marine mammals have declined five times. Humans and livestock now make up most of the total mammal weight, with wild mammals accounting for only 4%. These changes are part of the Holocene extinction, a major loss of species.

Since the late 20th century, protected areas and conservation efforts, such as reintroducing wolves in the U.S., have helped protect some wild mammals. However, many species are in worse condition now than in the past. Hundreds of species are critically endangered, and climate change also harms mammal populations.

Some pesticides, like insecticides, may harm specific bird species. A study found that 51 bird species are critically endangered, and eight may be extinct or near extinction. Nearly 30% of bird extinctions are due to hunting for the pet trade. Deforestation from logging and farming also threatens birds by destroying their homes and food sources.

Plants are vital for human survival but have not received as much attention as animals in conservation efforts. About one-third of all land plant species are at risk of extinction, and 94% have not yet been evaluated for their conservation status. Protecting plants is important to reduce harm to higher levels of the food chain.

In 2022, scientists warned that one-third of tree species are threatened with extinction. This could disrupt ecosystems by affecting carbon, water, and nutrient cycles. Forests are damaged by logging, fires, and overharvesting firewood. The Global Tree Assessment found that 17,510 (29.9%) tree species are at risk of extinction, and 142 are already extinct or extinct in the wild.

Some forest management practices, such as selective logging and thinning, can help protect tree biodiversity. Without action, recovery of forest species may take 50 years to match primary forests or 20 years to restore 80% of species.

Human activities have caused many species to go extinct and threaten more today. Organizations like IUCN and the Royal Botanic Gardens, Kew, have highlighted the urgency of these issues.

Causes

The main causes of current biodiversity loss are:

• Habitat loss, fragmentation, and degradation; for example, habitat fragmentation for commercial and agricultural uses (specifically monoculture farming).
• Land use intensification (and ensuing land loss/habitat loss); a significant factor in loss of ecological services due to direct effects as well as biodiversity loss.
• Nutrient pollution and other forms of pollution (air and water pollution).
• Overexploitation and unsustainable use (for example, unsustainable fishing methods, overfishing, overconsumption, and human overpopulation).
• Invasive species that effectively compete for a niche, replacing indigenous species.
• Climate change (e.g., extinction risk from climate change, effects of climate change on plant biodiversity).

Jared Diamond describes an "Evil Quartet" of habitat destruction, overkill, introduced species, and secondary extinctions. Edward O. Wilson suggested the acronym HIPPO for the main causes of biodiversity loss: Habitat destruction, Invasive species, Pollution, human overpopulation, and Over-harvesting.

Habitat destruction (also termed habitat loss) occurs when a natural habitat is no longer able to support its native species. The organisms once living there have either moved elsewhere or are dead, leading to a decrease in biodiversity and species numbers. Habitat destruction is in fact the leading cause of biodiversity loss and species extinction worldwide.

Humans contribute to habitat destruction through the use of natural resources, agriculture, industrial production, and urbanization (urban sprawl). Other activities include mining, logging, and trawling. Environmental factors can contribute to habitat destruction more indirectly. Geological processes, climate change, introduction of invasive species, ecosystem nutrient depletion, water and noise pollution are some examples. Loss of habitat can be preceded by an initial habitat fragmentation. Fragmentation and loss of habitat have become one of the most important topics of research in ecology as they are major threats to the survival of endangered species.

For example, habitat loss is one of the causes in the decline of insect populations (see the section below on insects).

The direct effects of urban growth on habitat loss are well understood: building construction often results in habitat destruction and fragmentation. This leads to selection for species that are adapted to urban environments. Small habitat patches cannot support the level of genetic or taxonomic diversity they formerly could, while some more sensitive species may become locally extinct. Species abundance populations are reduced due to the reduced fragmented area of habitat. This causes an increase of species isolation and forces species toward edge habitats and to adapt to foraging elsewhere. Additionally, edge effects often result in altered light, temperature, and humidity conditions that change vegetation structure and microhabitat suitability, further reducing biodiversity in fragmented urban patches. Urban environments also favor fast-reproducing, mobile species, contributing to biotic homogenization and the global decline of ecological uniqueness.

Infrastructure development in Key Biodiversity Areas (KBA) is a major driver of biodiversity loss, with infrastructure present in roughly 80% of KBAs. Infrastructure development leads to conversion and fragmentation of natural habitat, pollution, and disturbance. There can also be direct harm to animals through collisions with vehicles and structures. This can have impacts beyond the infrastructure site. For example, chronic noise from roads can interfere with bird song used in mating and territory defense, reducing reproductive success. Artificial lighting can disrupt nocturnal foraging patterns, predator-prey interactions, and migratory navigation in species such as bats, amphibians, and sea turtles. Infrastructure can also create ecological traps, where animals are drawn to altered environments that ultimately reduce their fitness or survival. Furthermore, road mortality and bird collisions with buildings and power lines cause direct harm to wildlife, with cascading impacts across trophic levels. These impacts often extend well beyond the development footprint and may disrupt landscape connectivity critical for migration and climate adaptation. Fragmented landscapes also impede species' range shifts in response to climate change, making it harder for populations to track suitable environmental conditions and increasing extinction risk.

Humans are changing the uses of land in various ways, and each can lead to habitat destruction and biodiversity loss. The 2019 Global Assessment Report on Biodiversity and Ecosystem Services found that industrial agriculture is the primary driver of biodiversity collapse. The UN's Global Biodiversity Outlook 2014 estimated that 70% of the projected loss of terrestrial biodiversity is caused by agriculture use. This is supported by more recent findings from the 2022 Global Land Outlook report by the UN Convention to Combat Desertification, which states that over 50% of agricultural land is moderately or severely degraded. According to a 2005 publication, "Cultivated systems […] cover 24% of Earth's surface." The publication defined cultivated areas as "areas in which at least 30% of the landscape is in croplands, shifting cultivation, confined livestock production, or freshwater aquaculture in any particular year." As of 2023, approximately 38% of the Earth's terrestrial surface is used for agriculture, including grazing and crop production, making it the dominant land use globally.

More than 17,000 species are at risk of losing habitat by 2050 as agriculture continues to expand to meet future food needs (as of 2020). A global shift toward largely plant-based diets would free up land to allow for the restoration of ecosystems and biodiversity. In the 2010s, over 80% of all global farmland was used to rear animals. Recent FAO data shows that livestock systems occupy about 77% of agricultural land while providing less than 20% of the global calorie supply—highlighting an imbalance between land use and nutritional output.

As of 2022, 44% of Earth's land area required conservation attention, which may include declaring protected areas and following land-use policies. Additionally, a 2023 analysis in Science Advances concluded that at least 30% of land must be actively protected and ecologically restored by 2030 to meet global biodiversity goals, aligning with the Kunming-Montreal Global Biodiversity Framework agreed upon at COP15.

Air pollution adversely affects biodiversity. Pollutants are emitted into the atmosphere by the burning of fossil fuels and biomass, for example. Industrial and agricultural activity releases the pollutants sulfur dioxide and nitrogen oxides. Once sulfur dioxide and nitrogen oxide are introduced into the atmosphere, they can react with cloud droplets (cloud condensation nuclei), raindrops, or snowflakes, forming sulfuric acid and nitric acid. With the interaction between water droplets and sulfuric and nitric acids, wet deposition occurs and creates acid rain.

A 2009 review studied four air pollutants (sulfur, nitrogen, ozone, and mercury) and several types of ecosystems. Air pollution affects the functioning and biodiversity of terrestrial as well as aquatic ecosystems. For example, "air pollution causes or contributes to acidification of lakes, eutrophication of estuaries and coastal waters, and mercury bioaccumulation in aquatic food webs."

Noise generated by traffic, ships, vehicles, and aircraft can affect the

Impacts

Biodiversity loss harms how ecosystems work. This affects humans because ecosystems can no longer provide the same level of services, such as pollinating crops, cleaning air and water, breaking down waste, and offering forest products, as well as places for recreation and tourism.

A 2012 review of research from the past 20 years included two important findings:

• "There is clear evidence that losing biodiversity reduces how well ecosystems use important resources, create food, and recycle nutrients"; and
• "The effects of losing biodiversity on ecosystems may be as serious as the effects of other major global environmental changes."

Permanent loss of species (extinction) is more extreme than changes in species numbers in a specific area. However, even small changes from a healthy, balanced ecosystem can greatly affect food webs and chains. When one species disappears, it can cause other species to also disappear (coextinction). This may reduce overall biodiversity unless the ecosystem can return to a different stable state.

For example, a study on grasslands found that ecosystems with more diverse plant life are better at keeping their productivity stable during extreme weather.

In 2019, the United Nations’ Food and Agriculture Organization (FAO) released its first report on the state of the world’s biodiversity for food and agriculture. It warned that "Many important parts of biodiversity for food and agriculture, including genetic, species, and ecosystem levels, are declining."

The report also stated, "Many factors that harm biodiversity for food and agriculture, such as overuse of resources, pollution, and poor land and water management, are partly caused by farming practices. Switching to growing fewer types of crops and animals intensively is a major cause of biodiversity loss and reduced ecosystem services."

To reduce biodiversity loss from farming, the FAO encourages using "biodiversity-friendly practices in farming, raising livestock, managing forests, and fishing."

The World Health Organization (WHO) has studied how biodiversity and human health are connected. It explained, "Biodiversity and health are linked in many ways. For example, the variety of species and genetic traits provides food and medicine." The ongoing loss of biodiversity may increase the risk of future diseases, like the COVID-19 pandemic.

Medicinal and aromatic plants are used in traditional medicine, cosmetics, and food. The WHO estimated in 2015 that "about 60,000 species are used for their medicinal, nutritional, and aromatic properties." There is a global trade in plants for medicinal use.

Biodiversity helps develop medicines. Many medicines come from natural sources, either directly or indirectly. Some of these natural sources are from ocean ecosystems. However, overharvesting without proper rules (bioprospecting) can lead to overuse of resources, harm ecosystems, and reduce biodiversity. People collect plants for traditional medicine by growing them or taking them from the wild. In both cases, managing these resources in a way that protects the environment is important.

Proposed solutions

Scientists are studying ways to solve biodiversity loss and climate change at the same time. Both problems require protecting enough natural areas and choosing the right places to protect them. A 2020 study showed that, in addition to the 15% of land already protected, 35% of land is needed to protect important areas for biodiversity and help stabilize the climate.

Other steps to protect biodiversity include reducing the causes of changes in land use, improving agriculture efficiency, and reducing the need for animal farming. This could be done by increasing the use of plant-based foods.

Many governments have protected parts of their land through the Convention on Biological Diversity (CBD), an international agreement signed in 1992–3. The Aichi Biodiversity Targets, part of the CBD’s plan from 2011–2020, included a goal to protect 17% of land and inland water areas and 10% of coastal and ocean areas by 2020.

By 2020, only six of the 20 Aichi Targets were partially met. A 2020 CBD report said that without changes, biodiversity will keep declining because of unsustainable ways of producing and using resources, population growth, and new technologies. The report also noted that Australia, Brazil, Cameroon, and the Galapagos Islands (Ecuador) each lost one animal species to extinction in the previous ten years.

After this, leaders from 64 countries and the European Union promised to stop harming the environment and restore nature. This promise was not signed by leaders from some major polluters, including China, India, Russia, Brazil, and the United States. Some experts say the United States’ refusal to join the CBD is slowing global efforts to stop species loss.

Scientists say even meeting the 2020 targets would not have significantly reduced extinction rates. Others argue the CBD does not go far enough and suggest the goal should be zero extinctions by 2050 and cutting the harm from unsustainable food production by half. Some also say the CBD’s goals are not legally required, which is a problem.

In December 2022, all countries except the United States and the Holy See signed the Kunming-Montreal Global Biodiversity Framework at a United Nations meeting. This plan aims to protect 30% of land and oceans by 2030. It also includes 22 other goals to reduce biodiversity loss. At the time, only 17% of land and 10% of oceans were protected. The agreement includes protecting Indigenous peoples’ rights and changing policies that harm biodiversity, but it does not protect species as strongly as the Aichi Targets. Critics say the agreement is not enough and that the process was too fast.

In 2019, the Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services (IPBES) released a report saying up to one million species face extinction due to human activity. IPBES is an international group that works on biodiversity, similar to the Intergovernmental Panel on Climate Change (IPCC), but focuses on ecosystems instead of climate change.

The United Nations’ Sustainable Development Goal 15 (SDG 15), "Life on Land," includes goals to protect biodiversity. One of its targets is to reduce habitat destruction, stop biodiversity loss, and protect endangered species by 2020. This target uses the Red List Index as a measure of progress.

Nearly three-quarters of bird species, two-thirds of mammals, and more than half of hard corals live in World Heritage Sites, even though these areas cover less than 1% of Earth. Countries with World Heritage Sites can include them in their national plans to protect biodiversity.