Plastic Planet
By SANTA FE INSTITUTE
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Over time, living systems have adapted to transform waste, with organisms such as dung beetles playing a crucial role in decomposing the feces of other species.
However,
managing waste continues to be a significant challenge within human societies.
As the world population continues to grow and
rapidly urbanize — two-thirds of humans will be city dwellers by 2050,
according to the United Nations — our waste is driving a mounting worldwide
crisis. Microplastics blanket the planet and infiltrate our bodies, wastewater
pollutes our waterways, and greenhouse gas emissions are driving global climate
change.
“We as a society tend to ignore the unpleasant side of our production,” says Mingzhen Lu, an Assistant Professor at New York University and former SFI Omidyar Complexity Fellow.
Lu and SFI Professor Chris Kempes are
co-corresponding authors on a new paper published in Nature Cities that explores waste production as a
function of urban systems.
Findings and Implications for Urban Planning
“The key question is whether waste is
produced more or less efficiently as systems scale up, and how big a recycling
burden there is as a consequence,” says Kempes.
To address this question, the authors used scaling theory to analyze waste products — municipal solid waste, wastewater, and greenhouse gas emissions — from more than one thousand cities around the world.
Scaling theory has been used in biology to describe how organism
physiology changes with body mass, and it proved relevant for understanding how
waste production scales with the growth of a city.
“Scaling theory allowed us to extract
overarching broad stroke patterns and transcend the individuality of each
city,” explains Lu.
The resulting patterns show distinct differences in waste production as cities grow. Solid waste scales linearly — because it is tied to individual consumption, it increases at the same rate as population growth.
In contrast, wastewater production scales superlinearly while emissions scale sub-linearly. In other words, bigger cities contribute disproportionately more liquid waste than smaller cities, but expel fewer greenhouse gasses.
The results suggest an economy of scale for emissions as
growth typically brings more efficient energy and transportation
infrastructure, but a diseconomy for liquid waste.
Cities tend to deviate from the universal
scaling law as they grow wealthier. Cities with higher per-capita GDP generate
more waste across the board, which underscores the relationship between waste
generation and economic growth.
Towards a New Science of Waste
The findings emphasize the need for a new
science of waste that can help predict the future state of urban ecosystems and
inform policies to reduce waste and enhance sustainability.
“Fungi figured out how to decompose lignin
waste from trees and created sustainable ecosystems that have lasted hundreds
of million years,” says Lu. “We take it in and throw it away — we can no longer
overlook waste from our societies.”
Reference: “Worldwide scaling of waste
generation in urban systems” by Mingzhen Lu, Chuanbin Zhou, Chenghao Wang,
Robert B. Jackson and Christopher P. Kempes, 17 January 2024, Nature Cities.
DOI:
10.1038/s44284-023-00021-5