Scientific alert: we have already passed seven of the nine critical thresholds for life on Earth.

BarcelonaJust two years ago the Earth was already in the ICU, when scientists confirmed that six critical thresholds for life on our planet had been crossed. These are nine indicators that make Earth a habitable place, like the vital signs examined during a medical checkup, from climate to freshwater use to the destruction of the ozone layer. For each of these nine indicators, limits have been established that should not be exceeded so that our planet remains a "safe" place for life. Well, in 2025, we have still exceeded the critical limit for another of the indicators, so that seven of the nine are now in the red, according to a new report from the Planetary Boundaries Science Lab at the Potsdam Institute for Research.

The new vital sign that has crossed the safe limit is ocean acidification, which measures the pH of seawater. The oceans are already too acidic because they contain too much CO₂. For the first time this year, in fact, this acidification is considered to exceed the limits set by scientists as safe.

Seawater captures nearly a third of the CO₂ we emit into the atmosphere. That's why The oceans are great regulators of the climateBut the excess CO₂ they are increasingly absorbing is causing surface pH to drop, which has already led to an increase in water acidity of between 30% and 40% since the pre-industrial era. Beyond laboratory analyses, this excess CO₂ in the water is already being felt in marine ecosystems: "Cold-water corals, tropical reefs, and Arctic marine fauna are particularly at risk as acidification expands and intensifies." "Small marine snails, called pteropods, are already showing damage to their shells." Since these animals are an important food source for many species, their decline is affecting the entire food chain, also impacting fisheries.

Ocean acidification has thus become "the seventh boundary breached, pushing humanity even further beyond the safe zone for civilization," warns the Potsdam Institute. The only two indicators that remain in good condition are the destruction of the ozone layer, which has receded, and the aerosol load, two indicators that remain at safe levels precisely because the international community took action. In the first case, the Montreal Protocol was adopted, which banned chemicals that destroyed the ozone layer, a step that helped this layer recover. And in the second case, the regulation of maritime transport was also added, which has reduced the levels of harmful aerosols in the atmosphere.

Other indicators transferred

The other six indicators that have been surpassed are climate change, biosphere integrity, land systems change (such as deforestation), freshwater use, biogeochemical fluxes, and pollutants. All of these indicators show increasing trends in deterioration. Scientists must slightly modified its classification compared to the 2023 study, which included eight indicators (six of which had also been exceeded), and consolidated the indicators analyzing nitrates and phosphorus into a single one, that of biogeochemical fluxes, which also exceeded safe limits, adding others such as the ozone layer. "In more than three-quarters of terrestrial support systems, we are not in the safe zone. Humanity is pushing beyond the limits of a safe operating space, which increases the risk of destabilizing the planet," warned Johan Rockström, director of the Potsdam Institute for Climate Impact Research.

"The movement we're seeing is absolutely in the wrong direction. The ocean is becoming more acidic, oxygen levels are falling, and marine heatwaves are increasing. This increases pressure on a system vital to stabilizing conditions on the planet. Warming and deoxygenation affects everything from coastal fisheries to the open ocean. The consequences are widespread, impacting food security, global climate stability, and human well-being," added Levke Caesar, co-leader of the Planetary Boundaries Science Lab.

Renowned oceanographer Dr. Sylvia Earle also sounded the scientific alarm: "The ocean is the lifeblood of our planet. Without healthy seas, there is no healthy planet. For billions of years, the ocean has been the great stabilizer of the Earth: generating the stabilizing pattern of the Earth. Every day, acidification is a red flag on the Earth's stability control panel. If If we ignore it, we risk collapsing the very foundation of our living world.