Human activity is profoundly reshaping Earth’s fundamental operations. The scale of these transformations has prompted the consideration of a new geological epoch defined by human influence. Driven by a rapidly growing population and increasing consumption, these widespread changes to the planet’s land, water, and air interact in complex ways, leading to substantial shifts in natural systems.
Transformation of Land and Soils
Humanity’s alteration of the Earth’s terrestrial surface is one of the most visible forms of environmental change, with over half of the planet’s ice-free land modified. The primary driver of this transformation is the expansion of agriculture. Converting natural landscapes like forests and grasslands into farmland reorders ecosystems, removes native vegetation, and frequently leads to monoculture. This homogeneity reduces biodiversity and makes crops more susceptible to pests and disease.
To boost yields, modern agriculture relies on chemical inputs. The application of nitrogen and phosphorus fertilizers can alter the chemical composition of soils, and their runoff pollutes adjacent waterways. Pesticides used to control insects and weeds can harm non-target organisms and persist in the environment, while combined with tillage, can accelerate soil erosion.
The growth of cities and their supporting infrastructure also reshapes the land. Urbanization replaces permeable soil with impervious surfaces like concrete and asphalt. This prevents water from soaking into the ground, which disrupts local water cycles, increases surface runoff, and elevates flood risk. These built environments also absorb and retain more heat, creating “urban heat islands.”
Extracting natural resources also causes dramatic changes to the land. Mining for minerals and fossil fuels can involve removing entire hilltops or creating vast open pits, displacing enormous quantities of earth. This process destroys habitats and can contaminate soil and water with pollutants. Widespread deforestation, driven by logging and land clearing, removes forest ecosystems that support a vast array of life.
Modification of the Atmosphere and Climate
Human activities have fundamentally altered the Earth’s atmosphere, leading to observable changes in the global climate. This is driven by enhancing the natural greenhouse effect, where certain gases trap heat. The accumulation of these gases is causing a steady rise in global average temperatures, which is linked to an increase in the frequency and intensity of extreme weather events. The scientific consensus attributes the current warming trend to this human-induced expansion of the greenhouse effect.
The most significant of these human-emitted gases is carbon dioxide (CO2), released through burning fossil fuels for energy and transportation. Deforestation is another major source, as forests that would normally absorb CO2 are cut down, releasing stored carbon. As of 2023, atmospheric CO2 concentrations had risen to 51% above pre-industrial levels.
Methane is another potent greenhouse gas, emitted from agricultural activities like livestock farming, waste decomposition in landfills, and natural gas extraction. Although it remains in the atmosphere for a shorter period than CO2, its warming effect is substantially more powerful in the short term. Nitrous oxide, released from nitrogen-based fertilizers, is also a long-lived contributor to atmospheric warming.
Reshaping Waterways and Oceans
One of the most direct forms of alteration is the physical restructuring of waterways. The construction of dams on rivers is a widespread practice, impeding the natural flow of more than 60% of the world’s major rivers. These structures are built for power generation, water storage, and flood control, but they alter river ecosystems by trapping sediment, changing flow regimes, and blocking fish migration.
Humans have also reshaped waterways by creating canals and irrigation channels that divert water from its natural course. These diversions support agriculture and human settlements but can reduce downstream water availability, impacting ecosystems and communities. This redirection of water alters the hydrology of entire regions and has contributed to the degradation of many wetlands.
Chemical alteration from pollution is another pervasive issue. Runoff from agricultural lands carries excess fertilizers into rivers, which flow into the ocean. These nutrients can cause eutrophication, an overgrowth of algae that consumes oxygen in the water, creating “dead zones” where marine life cannot survive. Industrial and urban areas contribute other pollutants, including heavy metals and toxic chemicals.
The oceans are also absorbing a significant portion of excess atmospheric carbon dioxide, leading to ocean acidification. This decrease in pH makes it more difficult for marine organisms like corals and shellfish to build their skeletons and shells. Compounding this is the vast amount of plastic waste entering waterways, which breaks down and poses a physical and toxic threat to marine animals.
Impacts on Biodiversity
The cumulative effect of these alterations to land, air, and water is a profound impact on Earth’s biodiversity. The changes to habitats, the chemical environment, and climate are driving a “sixth mass extinction” caused by human activities. Current extinction rates are estimated to be up to 100 times faster than the natural background rate.
The primary driver of this biodiversity loss is habitat destruction and fragmentation. As forests are cleared for agriculture, cities expand, and rivers are dammed, the spaces where species live are eliminated or broken into patches too small to support viable populations. This loss of habitat is the most significant threat to threatened species.
Human activities have also facilitated the spread of invasive species around the globe. These are plants, animals, and pathogens introduced to ecosystems where they do not naturally occur. Lacking natural predators, invasive species can outcompete native organisms for resources, disrupt food webs, and introduce diseases.
This restructuring of the planet’s living systems involves both loss and rearrangement. While many species are declining, others that thrive in human-altered landscapes are becoming more common. This leads to a homogenization of ecosystems, where a few resilient species dominate and the unique variety of life that characterizes different regions is diminished.