Massive Human Impact Measured

New studies show the wildly disproportionate effect humans have had on life on Earth.

Our planet’s 7.6 billion humans represent just 0.01 per cent of all living things, but that one species has caused the loss of 83 per cent of all wild mammals and half of plants, according to research from the Weizmann Institute of Science in Israel, published in the Proceedings of the National Academy of Sciences.

The work was based on comprehensive estimates of the weight of every class of living creature.

Researchers calculated biomass using data from hundreds of studies, which used a range of techniques including satellite imagery and gene sequencing.

They assessed the biomass of different classes of organisms and mapped them against environments that such life could live in across the world.

Using carbon as the key measure, they found all life on Earth contains 550 billion tonnes of the element.

The analysts say bacteria make up 13 per cent of life on Earth, while plants represent 82 per cent That leaves all other creatures from insects and fungi to the largest quadrupeds, making up just 5 per cent of the world’s biomass.

“I was shocked to find there wasn’t already a comprehensive, holistic estimate of all the different components of biomass,” said lead author Professor Ron Milo.

“I would hope this gives people a perspective on the very dominant role that humanity now plays on Earth.”

Human activity has had such a profound, system-wide effect that some scientists consider this a new geological era – the Anthropocene.

The rise of corollary species such as the domestic chicken is considered one marker of the new era.

The study in question estimates poultry now makes up 70 per cent of all birds on the planet, leaving just 30 per cent in the wild.

Around 60 per cent of all mammals on Earth are livestock, mostly cattle and pigs, 36 per cent are human and 4 per cent are wild animals.

“It is pretty staggering,” said Prof Milo.

“In wildlife films, we see flocks of birds, of every kind, in vast amounts, and then when we did the analysis we found there are [far] more domesticated birds.

“It is definitely striking, our disproportionate place on Earth.

“When I do a puzzle with my daughters, there is usually an elephant next to a giraffe next to a rhino. But if I was trying to give them a more realistic sense of the world, it would be a cow next to a cow next to a cow and then a chicken.”

When the new estimates are compared with those for the time before humans became farmers, the study shows just one-sixth of wild mammals, from mice to elephants, remain today.

“Our dietary choices have a vast effect on the habitats of animals, plants and other organisms,” Prof Milo said.

“I would hope people would take this [work] as part of their world view of how they consume.

“I have not become vegetarian, but I do take the environmental impact into my decision making, so it helps me think, do I want to choose beef or poultry or use tofu instead?”

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Caring for our special habitat and its residents for 40 years!

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