Pollution is the presence of substances or energy in the environment at levels that have adverse effects on living organisms or cause damage to the natural environment. It can include air, water, soil and chemical contamination as well as long-lived greenhouse gases that build up in the atmosphere and lead to climate change.
Since groups of humans began to settle in permanent locations, pollution has accompanied them. Ancient cities were often noxious places, with garbage heaps and waste streams that favored the spread of population-decimating epidemics from cholera to plague. Modern industrialization has taken this pollution to new, pervasive and complex levels.
Air pollution is now one of the world’s leading environmental health risks, killing an estimated 7 million people worldwide in 2024 and contributing to heart disease, respiratory diseases, cancers, and other ailments. It is caused by a range of sources, including cookstoves and kerosene lamps, fossil fuel combustion (including coal, gas and oil), vehicle emissions, industrial processes, and wildfires.
Water pollution is also widespread, with toxic pollutants contaminating groundwater and surface water bodies such as rivers, lakes, seas, and oceans. The sources of water pollution are diverse, ranging from agricultural runoff and urbanisation to land clearing and mining, fertilisers, pesticides, and household chemicals.
Soil pollution is the accumulation of harmful substances in the soil that disrupts natural ecosystems and the health of living organisms. The causes of soil pollution are widespread and can be caused by the intensive use of fertilizers, the improper disposal of household and industrial wastes, or the burning of fossil fuels.