The mass of human-made objects may surpass the mass of living things by the end of 2020, according to scientists.

A new study suggests the mass embedded in human-made items - such as buildings, roads and machines - has doubled every 20 years for the past 100 years.

These findings underscore the increasing impacts that humans have on Earth, researchers say.

According to the study, since the first agricultural revolution humans have halved plant biomass, from around two teratonnes (2,000,000,000,000 tonnes) to the current value of around one teratonne.

This has been done through land-use changes such as agriculture and deforestation.

The increasing production and accumulation of human-made objects - referred to as anthropogenic mass - has also contributed to a shift in the balance between living and human-made mass.

In the study published in Nature, the authors write: "We find that Earth is exactly at the crossover point.

"In the year 2020, the anthropogenic mass, which has recently doubled roughly every 20 years, will surpass all global living biomass.

"On average, for each person on the globe, anthropogenic mass equal to more than his or her bodyweight is produced every week."

Ron Milo, from the Weizmann Institute of Science in Israel, and colleagues estimated changes in global biomass and human-made mass from 1900 to the present day.

They found that at the beginning of the 20th century, the mass of human-produced objects was equal to around 3% of total biomass.

But according to the paper, today human-made mass exceeds the overall global biomass, weighing in at around 1.1 teratonnes.

Over this period, overall biomass decreased slightly, whereas anthropogenic mass has increased rapidly and is now being produced at a rate of more than 30 gigatonnes (30,000,000,000 tonnes) per year.

Buildings and roads make up the majority of human-made mass, with other examples including plastics and machines.

Changes in the composition of this mass correspond to specific construction trends, such as the shift from using bricks to concrete in buildings from the mid-1950s and the use of asphalt for road paving in the 1960s.

The researchers also suggest that shifts in the total anthropogenic mass are linked to major events, such as continuous increases in construction after the Second World War.

The authors note that the exact timing of crossover is sensitive to definitions, so there may be some variability in the estimates.

They used dry-weight estimates - excluding water, but they suggest wet-mass estimates or different definitions of mass categories could still place the transition in mass balance within the past, present or future decade.

If current trends continue, human-generated mass, including waste, is expected to exceed three teratonnes by 2040, the researchers suggest.

They write: "This study joins recent efforts to quantify and evaluate the scale and impact of human activities on our planet.

"The impacts of these activities have been so abrupt and considerable that it has been proposed that the current geological epoch be renamed the Anthropocene.

"Our study rigorously and quantitatively substantiates this proposal."