As human populations and resource demands continue to grow, they put more pressure on Earth’s eight natural systems–for example, groundwater supplies, land area for wild animal habitats and ecosystems, and clean air. Scientists have determined how far these systems can be pushed until serious harm comes to the lifeforms that depend on those systems. But some experts argue that those
limits must be made more conservative, in order to truly protect humans and the planet.
Case in point: Aerosols, or fine particulates less than 2.5 microns in diameter, are released into the air by a range of industrial processes. Their rising concentrations are starting to alter monsoon rain patterns on which millions of people depend for growing food. Such weather patterns are global. But aerosols can also harm human lungs, and people in poorer regions often suffer more from particulate pollution. A limit of 0.25 to 0.50 aerosol optical depth, or AOD, an estimate of the amount of aerosols present in the atmosphere, demarcates how much the atmosphere can accommodate before severe changes kick in. But a “safe and just” limit of 0.17 AOD, takes into account the problem of local air pollution levels, which kill millions of people a year.
What the experts say: “Our latest work indicates that in 2023 the world had already surpassed the safe and just limit for seven of the eight boundaries,” writes Joyeeta Gupta, a professor of environment and development in the Global South at the University of Amsterdam and a professor at IHE Delft Institute for Water Education. “Only the aerosols limit has not been breached globally, although local aerosol boundaries have been crossed in many parts of the world. We have also found that in more than 50 percent of all places on Earth, at least two of the safe and just boundaries have been crossed.”
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