A Chinese research team has recently revealed the emerging risks of declining oxygen levels in large cities around the world, raising concerns over peoples health and the potential for sustainable development in major cities. A research team from Lanzhou University investigated oxygen balances and related risks in 391 cities worldwide with a population of more than 1 million. They studied the oxygen index, the ratio of oxygen consumption to oxygen production. The results of the study show that global urban areas, covering 3.8 percent of the global land surface, accounted for approximately 39 percent of terrestrial oxygen consumption during the 2001-2015 period, said Huang Jianping, leader of the research team from the College of Atmospheric Science at Lanzhou University. It is estimated that 75 percent of cities with a population of more than 5 million had oxygen indexes greater than 100. The study also revealed that high population density and large-scale urban expansion not only increase the consumption of natural resources but also reduce the stability of an ecosystem. Notably, people living in large cities with excessively large oxygen index values would likely be exposed to severe hypoxia in extremely calm weather, said Huang. The study results warn that the long-term hypoxia environment will bring great harm to urban populations. Also, with the lack of oxygen, urban residents might face more frequent occurrences of high-temperature heat waves and severe water withdrawals, he added. The study results have been published in the journal Environmental Science and Technology.
