United Nations estimates indicate that by 2050, the human population living in cities will be 68% of the global total. Currently it stands at 55%, but all indications are that the rural-to-urban exodus will intensify in the coming decades.
More people living in cities will mean greater waste production, posing challenges to urban management systems and to the realization of a true ‘sustainable development’.
A group of researchers analyzed more than a thousand cities around the world to understand how the increase in their populations affected waste generation, from municipal solid waste to wastewater, including greenhouse gas emissions.
“As a society, we tend to ignore the ugly side of our production,” says Mingzhen Lu of New York University and the first author of the article published in the journal ‘Nature Cities’.
The research revealed that urban solid waste production will increase proportionally to the growth of the urban population, since “they are associated with individual consumption,” hence, the more people, the more urban solid waste.
But regarding wastewater, the trend will be much stronger. According to the experts, as the number of people living in cities increases, the volume of wastewater will rise “at a rate faster than linear,” unlike solid waste.
However, more people in cities will not necessarily imply a proportional increase in greenhouse gas emissions. In other words, if the city doubles its number of inhabitants, the emissions increase will be less than double, which the researchers call sublinear growth, explaining that this should be due to greater efficiency, for example, of public transportation.
Building on the study of population trends across thousands of cities and the impacts of increasing numbers of inhabitants, they conclude that “the energy efficiency of public transport systems increases with city size and population density due to the increased use of public transport,” they write in the article.
Therefore, they suggest that large cities will, on average, be more energy-efficient the more people live there. The same does not apply to water management, which they say will be less efficient as the urban population grows.
Alongside all this, they state that cities with the highest levels of income are the ones that generate more waste, “which underlines the strong link between waste generation and economic growth.” Therefore, they argue that the increase in waste production “appears to be a natural consequence of economic growth.”
Consequently, so that human societies globally might achieve climate neutrality, the authors argue that it is necessary to decouple economic growth from waste generation, and they point to examples as follows: San Francisco, in the United States of America (USA), which produces less per capita municipal solid waste than any other North American city, and cities in Japan, a country that produces one-third per capita municipal solid waste when compared with the USA.
“Increases in Gross Domestic Product often improve the quality of life of people living in cities, so we need to break the link between rising economic prosperity and per-capita waste production,” they point out in the study.
Mingzhen Lu considers that “studying how cities produce waste is only the first step,” suggesting that we need to “find a way to close the material loop.” And he adds that “natural ecosystems and their organisms,” such as bacteria and fungi, “have figured out how to deal with nature’s waste for millions of years. We can too.”
