Science

Our impact on Earth’s ecosystems and biodiversity – in graphics

Aerial view of farmers transplanting rice, Madagascar. December 2011.

Lorraine Bennery / naturepl.com

Biodiversity: A status report

If we are to begin to rebalance our relationship with nature, we must first establish how out of kilter things are. But ecosystems are complex and no single measure can capture all the changes human activities have caused.

Nevertheless, there are various ways of auditing biodiversity and humanity’s impact on it, from extinctions and species richness to land use and how much of the planet is set aside for nature. Almost all of them paint a worrying picture

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Perhaps the most eye-catching metric of humanity’s impact is in our acceleration of the rate of extinctions.

The background or natural rate is 0.1 to 2 extinctions per million species per year. Data from the International Union for Conservation of Nature’s Red List of Threatened Species suggests a rate of 34 extinctions per million species per year now. It documents at least 680 extinctions and a further 750 possible extinctions among 112,400 species in the past 500 years, with mammals and amphibians hardest hit among vertebrates.

In recent years, warming, acidifying oceans have caused a drop in coral species. Looking at how many species are considered vulnerable or endangered, the group under the most pressure is the cycads, a group of tropical palm-like plants. Two other plant groups, dicots and conifers, are also up there.

The Red List covers fewer than 5 per cent of the world’s known species. The Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services (IPBES) says that a further half a million terrestrial species of animals and plants may already be doomed to extinction.

There are many taxonomic groups for which no firm conclusions can be drawn due to insufficient data. One is insects. A recent review concluded that, “Although a flurry of reports has drawn attention to declines in insect abundance, biomass, species richness, and range sizes, whether the rates of declines for insects are on par with or exceed those for other groups remains unknown.”

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In recent years, warming, acidifying oceans have caused a drop in coral species. Looking at how many species are considered vulnerable or endangered, the group under the most pressure is the cycads, a group of tropical palm-like plants. Two other plant groups, dicots and conifers, are also up there.

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The Red List covers fewer than 5 per cent of the world’s known species. The Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services (IPBES) says that a further half a million terrestrial species of animals and plants may already be doomed to extinction.

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There are many taxonomic groups for which no firm conclusions can be drawn due to insufficient data. One is insects. A recent review concluded that, “Although a flurry of reports has drawn attention to declines in insect abundance, biomass, species richness, and range sizes, whether the rates of declines for insects are on par with or exceed those for other groups remains unknown.”

LAND USE

A less granular measure of humanity’s impact is given by various measures of the extent to which we control Earth’s surface.

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Infrastructure and intensively managed cropland, pasture and forest occupies more than half of Earth’s ice-free land surface, with much of the remaining land also highly modified. Human use now directly affects more than 70 per cent of Earth’s ice-free surface, with wilderness largely confined to a few areas of the Arctic, the Amazon rainforest, the Sahara desert and the Australian interior.

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Over 25 per cent of forests have been permanently cleared and more than half of the original 12.6 million square kilometres of wetlands have been drained. Of the approximately 16 million km2 of tropical rainforest that originally existed, less than 9 million km2 remain. The current rate of deforestation is 160,000 km2 per year, a loss of approximately 1 per cent of original forest a year.

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In intensively farmed areas of the world, the amount of biomass human activities extract from the land amounts to up to 100 per cent of what natural conditions would allow to grow. One result has been a decline in soil organic carbon, a measure of soil fertility, in many parts of the world. The decline in species richness is also most marked in these regions.

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None of these metrics account for the oceans, which cover some 70 per cent of Earth’s surface. Here our impacts are less easily quantifiable, but the effects of overfishing and pollution are such that only some 3 per cent of the world’s oceans are considered true wilderness.

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ECOSYSTEM INTACTNESS

Extinction rates tell us about the fates of individual species, but they don’t capture the effects of humanity’s land grab on functional diversity, a measure of overall ecosystem health. One attempt to do so is the Living Planet Index, produced by the WWF in association with the Zoological Society of London. It is computed using the size of 20,811 populations of 4392 species of mammals, birds, fishes, reptiles and amphibians from terrestrial, freshwater and marine habitats around the world. The 2020 update shows that, since 1970, the global abundance of vertebrates has declined by 68 per cent.

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The Biodiversity Intactness Index is an alternative measure of how much of pre-industrial biodiversity remains. This is seen as severely damaged if the number is below 90 per cent (in other words, a loss of more than 10 per cent of biodiversity). The global figure is currently 79 per cent, and falling.

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PROTECTED AREAS

One success story is the proportion of land important for biodiversity that has some form of protection. This has been growing across the world. The Netherlands Environmental Assessment Agency added up existing commitments to restoration projects in 115 countries and found that they come to about 10 million square kilometres, roughly the size of China, or just under 7 per cent of total world land surface area. How that squares with reality on the ground is another question.

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