Overview

• Ocean acidification is now beyond the safe boundary for the first time, with surface pH down about 0.1 since preindustrial times, equivalent to a 30–40% rise in acidity.
• Aragonite saturation has fallen below the 80% preindustrial benchmark, with observed damage to corals, pteropods and other shell‑forming organisms that underpin marine food webs.
• Only stratospheric ozone and atmospheric aerosol loading remain within the safe zone, helped by regulations such as the Montreal Protocol and recent aerosol controls.
• Other transgressed boundaries include climate change, biosphere integrity, land‑use change, freshwater use, disrupted nitrogen and phosphorus cycles, and novel entities/chemical pollution.
• Researchers describe a growing risk of systemic destabilisation rather than an immediate collapse and call for swift cuts to fossil‑fuel emissions, tighter chemical oversight and ecosystem restoration.