Weight on our shoulders: human-made materials outweigh living things

A study conducted by a team of researchers from the Weizmann Institute in Israel has revealed human-made materials now outweigh all other living things on the planet. The team investigated previously published datasets by dividing human-made materials into six categories; consisting of bricks, metals, asphalt, aggregates (materials mixed with cement), and concrete, alongside “other” materials such as wood, glass, and plastic, from 1900 to present day. They discovered materials such as aeroplanes, clothes, and houses now exceed the approximate 9 million biological species thought to exist on Earth.

The amount of plastic is greater in mass than all marine and land animals combined, yet accounts for just 1% of infrastructure mass. The mass of Earth’s entire animal population – some 4 billion tonnes – is now half that of the plastic ever manufactured: around 8 billion tonnes. Despite this, the bulk of anthropogenic mass is composed of buildings and infrastructure made from concrete and aggregate alongside metals, asphalt, and bricks – the building blocks of modern civilisation. 

aerial photography of concrete roads
Concrete jungle: human-made infrastructure is taking over the natural environment. Image: Unsplash.

At the turn of the 20th century, human-made materials weighed some 35 billion tonnes. Today, it has grown to some 1.1 trillion. Since the Neolithic Revolution – the shift from forager to farmer or hunter-gatherer to settler approximately 12,000 years ago – humanity has almost halved global biomass. Now, human beings and their livestock outweigh all the planet’s wild mammals and birds by a factor of around 20. 

An increasing amount of the planet’s land is being used for agriculture; particularly growing crops, which has slashed global biomass. Between 2017 and 2018, 8% of land within the Green Belt – a policy employed by the UK government to control urbanisation – was changed to residential use.

“While modern agriculture utilises an increasing land area for growing crops, the total mass of domesticated crops is vastly outweighed by the loss of plant mass resulting from deforestation, forest management and other land-use changes. These trends in global biomass have affected the carbon cycle and human health.” 

2020 Weizmann Institute study

Around 90% of biological matter (by weight) is composed of plants; mainly shrubs and trees. Flora create habitats for many different organisms and act as a food source for most terrestrial organisms, whilst maintaining oxygen and carbon dioxide levels in the atmosphere via the process of photosynthesis. According to the authors of the Weizmann Institute study, the mass of Earth’s flora has remained somewhat steady as a result of a “complex interplay” of deforestation, forest regrowth, and vegetable regrowth encouraged by rising carbon dioxide levels in the atmosphere. 

aerial photography of forest
Large areas of land are being deforested for human use such as for agriculture. Image: Unsplash.

Evolution in socio-economic development corresponds with periods of increased or decreased impact. During the 1950s, following the war, the materials used in construction shifted from bricks to concrete. The Weizmann Institute study claims that human-made mass increased continuously by some 5% per year after the second world war; a period of considerable advances in consumption and industrial development. When the Iranian revolution kindled the 1979 oil crisis, a subsequent dip in human-made mass occurred. 

The scientists behind the study have chosen to support the Anthropocene Epoch theory: which argues the existence of a current period in the planet’s history where human influence is paramount. Many environmentalists propose the Anthropocene is an unofficial unit of geological time in which human activity is currently shaping the planet. Emily Elhacham, lead author of the study, and her colleagues stress “our study rigorously and quantitatively substantiates this proposal.”

Elhacham explains that the current estimate of plant biomass remains difficult to establish, so dating the study’s conclusions is difficult. The study presumes smaller animal and microbial populations have remained somewhat constant, yet this assumption still requires further investigation. 

Global biomass may have only decreased slightly since 1900, but the production rate of anthropogenic-made mass has increased to more than 30 gigatonnes (30,000,000,000 tonnes) per year. If the trend continues, human mass is thought to weigh more than three times as much as life on Earth by approximately 2040. 

By Hollie Tuffnell

Header image: Unsplash