Biodiversity loss

Biodiversity loss refers to the reduction in biological diversity within a specific area or across the entire planet. Biologists define biodiversity as the totality of genes, species, and ecosystems in a region. This loss can occur in two ways. It can be temporary if the damage is reversible through ecological restoration. However, if the damage cannot be undone, the loss becomes permanent. When a species disappears completely from Earth, it is called extinction. This ongoing process is sometimes called the Holocene extinction or the sixth mass extinction.

Most contemporary biodiversity loss is attributed to human activities that push planetary boundaries too far. A primary driver is habitat destruction, such as deforestation, which removes the homes animals and plants need to survive. Land use intensification, like monoculture farming, also reduces variety. Other significant factors include air and water pollution, over-exploitation of resources, and the spread of invasive species. Climate change is another growing threat. For example, coral reefs are biodiversity hotspots that could be lost by the year 2100 if global warming continues at current rates. While climate change is a major concern, habitat destruction is currently the larger driver of loss.

Scientists use several methods to quantify these losses. They often measure species richness, which is the number of different species in an area. They also look at local abundance, which is the number of individuals of a species found in a sample. By comparing these numbers over time, they can calculate the rate of decline. The International Union for Conservation of Nature (IUCN) maintains the Red List to track species at risk. In 2021, about 28 percent of the 134,400 species assessed were listed as threatened with extinction. This totaled 37,400 species, a massive increase from the 16,119 species listed as threatened in 2006.

Certain regions are more critical for conservation than others. These are known as biodiversity hotspots. These areas host a large fraction of the world's life despite covering a small area. Since 1988, the number of identified hotspots has grown from 10 to 34. Currently, these hotspots cover only 2.3 percent of the world's surface. However, they host 50 percent of all vascular plant species. Of the 34 hotspots, 16 are located in tropical regions. Tropical rainforests are especially vital, as they host more than half of the world's total biodiversity.

Different groups of living things show different patterns of decline. The World Wildlife Fund reported that wildlife populations declined by an average of 69 percent between 1970 and 2016. In the oceans, migratory fish populations have declined by 76 percent since 1970. Large "megafish" populations have even fallen by 94 percent. In terrestrial environments, earthworms are also struggling. In intensive agricultural fields, earthworm biomass has seen mean losses of 83 percent. This happens because tillage practices and land use decimate the soil and roots they rely on.

Plants and trees face significant risks as well. It is estimated that one-third of all land plant species are at risk of extinction. Specifically, the Global Tree Assessment found that 29.9 percent of tree species, or 17,510 species, are considered threatened. This could alter global carbon, water, and nutrient cycles. In freshwater ecosystems, which make up only 1 percent of Earth's surface, species are declining at twice the rate of land or ocean species. This is due to factors like water pollution and overfishing.

Efforts to stop these trends involve global policy and local action. The UN Convention on Biological Diversity works to conserve wilderness areas. However, meeting specific goals has proven difficult. For instance, of the 20 Aichi Biodiversity Targets set in 2010, only six were partially achieved by 2020. Despite these challenges, various management methods can help. In forests, selective logging or thinning can promote tree diversity. In agriculture, reducing tillage can help restore earthworm populations. Protecting biodiversity is essential because it maintains the complex systems that support all life on Earth.