Human activity is changing ecosystems at a speed and scale that place many species at risk, but plastic is not the single cause of a new extinction event. The Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services (IPBES) identifies five major direct drivers of biodiversity decline: changes in land and sea use, direct exploitation of organisms, climate change, pollution and invasive alien species. Their importance varies by ecosystem and region, and they often interact.
Habitat change removes and fragments living space
Conversion of forests, wetlands, grasslands and coastal habitats for agriculture, infrastructure, extraction or settlement can remove the resources a population needs. Roads, dams and other barriers can divide what remains into smaller patches. Fragmentation may restrict movement, reduce access to mates or food, and make small populations more vulnerable to fire, disease and local environmental change. The effect depends on the species, the quality of the remaining habitat and whether a connected landscape is still available.
Changes at sea include coastal development, seabed disturbance and altered freshwater flows. These pressures can affect nursery grounds and feeding areas, while fishing and shipping create additional risks. A global summary can identify broad patterns, but the mechanism behind a local decline must be established with evidence from that ecosystem.
Direct exploitation can reduce populations quickly
Hunting, fishing, logging and collection remove organisms directly. Where removals exceed reproduction, populations shrink; selective harvesting can also change age structure or remove particular traits. Bycatch and illegal trade can affect species that were not the intended target. Historical cases such as the dodo, great auk and Steller’s sea cow illustrate how human pressures can contribute to extinction, though each has its own chronology and evidence.
Exploitation can compound habitat change. A population already confined to a smaller area may have fewer refuges from harvest, while roads built through intact habitat can improve access for hunters. The pressures are analytically distinct, but their ecological effects need not be independent.
Climate, pollution and introduced species interact
Climate change shifts temperature, rainfall, ocean chemistry and the frequency of some extremes. Species may track suitable conditions, adapt, or decline; their options depend on mobility, generation time and available habitat. Climate pressure can make a population more vulnerable to disease or invasive predators, especially when the landscape is already fragmented.
Pollution includes far more than plastic: nutrients, pesticides, heavy metals, industrial chemicals, oil and discarded materials can affect organisms and habitats through different pathways. Plastic debris can injure or entangle wildlife, and small particles occur widely, but detecting plastic in an animal does not by itself demonstrate a population-level effect or prove that it caused an extinction. The exposure, dose and biological consequence must be measured.
Invasive alien species can prey on, compete with or spread disease to native species. They are particularly damaging on islands and in ecosystems where native organisms evolved without similar predators or competitors. Their effects can combine with habitat loss and changing climate, making prevention and early response important parts of conservation.
Why “sixth mass extinction” needs care
Scientists use mass extinction for episodes in the geological record when a large share of species disappears across a relatively short interval of geological time. Today’s extinction rates and the number of threatened species are serious concerns, but comparisons with ancient events depend on how extinction rate, time interval and incomplete records are measured. The phrase is a warning about scale and trajectory, not a claim that every region or group is already undergoing the same process.
The end-Cretaceous extinction was driven by an abrupt global catastrophe associated with the Chicxulub impact and its environmental consequences. Present biodiversity loss has different causes, operating unevenly and often through cumulative pressures. Late Quaternary megafauna declines offer another comparison in which climate change and human activity are evaluated together rather than reduced to one universal cause.
Assessing risk requires evidence at several scales: population trends, habitat condition, exploitation, climate exposure and pollution measurements. Conservation responses work best when they target the pressures actually documented for a species and region. Broad claims about plastic, climate or human activity should not replace that diagnosis.
Frequently asked questions
What are the main human pressures on biodiversity?
IPBES groups the major direct drivers as land and sea use change, direct exploitation, climate change, pollution and invasive alien species. Their relative importance differs among places and species.
Is plastic the main cause of current extinctions?
No. Plastic is one form of pollution. Global assessments identify several major drivers, including habitat change and direct exploitation, and plastic exposure alone does not prove a population-level effect.
Does science agree that a sixth mass extinction is already happening?
Scientists document elevated extinction risk and biodiversity decline, while the comparison with geological mass extinctions depends on rates, time intervals and incomplete records. The phrase should not imply identical causes or impacts everywhere.
Can climate change cause a species to become extinct?
It can contribute to decline when conditions shift beyond a species’ tolerance or its range cannot move, but impacts depend on biology and place. Climate effects often interact with habitat loss and other pressures.