The question of how many species are being lost per hour addresses the current biological crisis facing the planet. Scientists agree that Earth is experiencing the Sixth Mass Extinction, unique because it is the first one driven by Homo sapiens. The present rate of extinction is not merely elevated; it is estimated to be thousands of times higher than the natural rate that has prevailed over geological time. Analyzing the scale of this loss requires understanding the natural baseline and the specific metrics scientists use to measure this acceleration.
Defining the Scale of Species Loss
To understand the current crisis, scientists establish the natural rate of species loss, known as the Background Extinction Rate (BER). The BER is derived from the fossil record and reflects the typical rate at which species naturally disappear over time. It is generally estimated to be about one extinction per million species-years (E/MSY), though some analyses suggest the BER is closer to 0.1 E/MSY.
Comparing this historical baseline to today’s figures reveals dramatic acceleration. The current extinction rate is conservatively estimated to be 100 to 1,000 times higher than the BER, with some analyses suggesting the rate is up to 10,000 times higher. This increase indicates that the planet’s biodiversity is under unprecedented stress.
Expressing this metric in terms of species lost per unit of time provides a tangible sense of the scale. Estimates of total global species range from two million to 100 million, causing the number of species lost annually to vary widely. A widely cited estimate suggests the rate of loss is equivalent to approximately 30,000 species per year.
Converting that estimate answers the question: 30,000 species lost per year translates to a loss of approximately four species every hour. Other scientific estimates suggest a loss of 150 to 200 species per day, equaling 55,000 to 73,000 species annually. While these figures are debated due to the difficulty of documenting every extinction, they consistently show a loss rate vastly exceeding natural recovery capacity.
Methods Used to Calculate Extinction Rates
The high estimates of species loss rely primarily on predictive models rather than merely counting observed extinctions, which is a key distinction. The first method compares documented modern extinctions against the fossil-record-derived Background Extinction Rate. For example, the observed extinction rate for vertebrates is already up to 100 times higher than the background rate for that group, confirming the crisis is underway for well-studied species.
The second and most influential method uses the Species-Area Curve (SAC) model. This ecological principle relates the size of a habitat area to the number of species it can support, meaning larger areas hold more species. Conservation biologists use the SAC model in reverse, predicting that a percentage of habitat loss will inevitably lead to a corresponding percentage of species loss.
The high SAC estimates contrast with the low number of formally documented extinctions due to “Extinction Debt.” This debt describes the future, delayed extinction of species already doomed by past habitat destruction or fragmentation.
Species with long generation times, such as large trees or certain specialist animals, may persist for decades in fragmented habitats too small to support them long-term. These are effectively “living dead” populations committed to eventual extinction. The SAC model accounts for this debt, predicting the total number of species that will be lost once the ecosystem adjusts to its reduced size, explaining why predicted rates exceed observed ones.
The Primary Drivers of Species Decline
The accelerated extinction rate is driven by five major human-caused factors, often grouped under the acronym HIPPO. These drivers work in combination, placing immense pressure on ecosystems globally.
- Habitat destruction and fragmentation represents the single greatest threat to biodiversity. This destruction is overwhelmingly driven by the conversion of natural areas for agriculture, logging, mining, and urban expansion. Fragmentation breaks large habitats into isolated patches, limiting species movement, genetic exchange, and resource availability.
- Invasive species are often introduced accidentally or intentionally into new environments where they lack natural controls. These non-native species can quickly outcompete native flora and fauna, spread diseases, or act as novel predators, leading to the decline of vulnerable native populations.
- Pollution of air, land, and water degrades the quality of remaining habitats. This includes agricultural runoff causing oxygen depletion in aquatic environments, and the introduction of industrial chemicals and plastics disrupting the biological functions of organisms.
- Population (Human) growth and increased consumption rates multiply the impact of all other threats. The demand for food, energy, and resources directly fuels habitat conversion, overexploitation, and pollution on a global scale.
- Overexploitation refers to the unsustainable harvesting of wildlife populations, such as overfishing or excessive logging. This factor directly reduces the number of individuals in a species faster than they can naturally reproduce, leading to rapid population collapse and localized extinctions.
An overarching threat, Climate Change, interacts with all five factors, altering species ranges and disrupting the delicate balance of already weakened ecosystems.
Ecological Impacts of Rapid Biodiversity Loss
The sheer numbers of species lost only tell part of the story, as the disappearance of individual species profoundly affects ecosystem functionality. Every species plays a functional role, and their loss diminishes the natural services that support life.
These consequences include the loss of ecosystem services, the benefits humans derive from nature. A decline in biodiversity compromises essential functions like the purification of water and air, carbon sequestration by forests, and the pollination of global food crops.
The loss of species also leads to the disruption of trophic cascades, the complex energy pathways within a food web. Removing a single predator or dominant herbivore can cause a chain reaction, destabilizing the entire ecosystem structure and potentially triggering further extinctions.
Finally, the decline of populations results in genetic erosion, the reduction of genetic diversity within a species. This loss of variability makes remaining populations less resilient and less able to adapt to future environmental changes, such as new diseases or climate shifts, increasing their long-term vulnerability.