You\u2019re the product of stability on a planetary scale. Around 12,000 years ago, Earth warmed from an ice age into the relatively consistent climate that allowed humans to adopt agriculture, literally putting down roots. That stability, though, is now shattered, as more than 8 billion people rapidly heat the planet, ravage its ecosystems, and plunder its resources.\u00a0<\/p>\n
In a new report<\/a>, scientists warn that we\u2019ve crossed yet another \u201cplanetary boundary,\u201d a threshold that keeps Earth\u2019s systems hospitable to life \u2014 a sort of global resilience that allows the planet to absorb shocks. This time, it\u2019s the relentless acidification of the seas that\u2019s crossed into dangerous territory, threatening all manner of marine life, including the organisms at the base of the food web. Of the nine total planetary boundaries, this is the seventh that\u2019s been breached.\u00a0<\/p>\n \u201cWhat this health check again and again shows is that we have one interlinked, interconnected Earth system,\u201d said Levke Caesar, co-lead of the Planetary Boundaries Science Lab at the Potsdam Institute for Climate Impact Research and a co-author of the report. \u201cIt actually would be fatal if we just concentrate on climate change, because, as we see, there are six other boundaries that have been transgressed. And we\u2019re actually also increasing the pressure on all of these seven boundaries.\u201d<\/p>\n Think of a planetary boundary as a warning sign on a road. At the end of the road is a cliff, representing a tipping point, in which an Earth system dramatically changes, often irreversibly. Researchers are worried, for instance, that parts of the Amazon may be nearing a transformation from rainforests to savannas<\/a> due to the compounding crises of climate change and deforestation. If that\u2019s the cliff, the concept of a planetary boundary is a big yellow \u201cCLIFF AHEAD\u201d sign, a warning from scientists that we could be approaching a catastrophic shift.\u00a0<\/p>\n Or to use another metaphor: A planetary boundary is your doctor warning you that you have high blood pressure, and the tipping point is the ensuing heart attack. \u201cWe are setting the planetary boundaries in such a way that as long as we are within the safe operating space, we should prevent the crossing of tipping points,\u201d Caesar said.<\/p>\n Before ocean acidification was added to the list this year, the researchers warned that six other boundaries have already been crossed: The climate is changing rapidly; humans are using too much fresh water; we\u2019re driving species to extinction and transforming the biosphere; forests are shrinking; fertilizers are polluting water bodies; and \u201cnovel entities\u201d like chemicals and plastics are streaming into the environment.\u00a0<\/p>\n Ocean acidification is intimately intertwined with the planetary boundary of climate change because seawater absorbs carbon dioxide from the atmosphere, and indeed has soaked up a quarter of humanity\u2019s CO2 emissions. That\u2019s helped keep the planet from warming even faster, but also creates carbonic acid. Accordingly, the report notes that ocean acidity has grown 30 to 40 percent since widespread burning of fossil fuels started in the industrial era.<\/p>\n This is perilous news for oceanic lifeforms. Many organisms, like corals, mollusks, and crustaceans, build shells for protection, but carbonic acid reduces the amount of calcium carbonate available for them to do so. And what they do manage to build will be continuously eroded by the increasing acidity of seawater, requiring them to add new layers to their homes to keep up. \u201cAcidification affects a lot of marine organisms physiologically,\u201d said Peter Roopnarine, curator of geology at the California Academy of Sciences, who wasn\u2019t involved in the report. \u201cWhether that\u2019s for a properly functioning respiratory system, or for building an external or internal skeleton. It affects everything from the larvae, or the development of these organisms, all the way up to the adults.\u201d<\/p>\n Acidification and rising water temperatures also cause coral bleaching<\/a>, when the organisms get stressed and release the symbiotic algae that provide them energy. Because scientists have evidence that organisms are already being harmed in this way, the new report confirms that we\u2019ve crossed the planetary boundary for ocean acidification. \u201cThere\u2019s some real concern that as our water acidifies, that there will be fairly significant ecosystem impacts to the marine calcifying species,\u201d said Jennie Rheuban, a research specialist at the Woods Hole Oceanographic Institution, who wasn\u2019t involved in the report.<\/p>\n This acidification could also shake the very foundation of the oceanic food web. Phytoplankton are tiny photosynthetic organisms that soak up CO2 and expel oxygen<\/a>, just like plants on land. Indeed, these plankton gobble up half of the CO2 sequestered worldwide by photosynthesis, and produce half of Earth\u2019s atmospheric oxygen.\u00a0<\/p>\n Unfortunately, many species of phytoplankton build shells and may struggle<\/a> as the oceans relentlessly acidify. These organisms sequester loads of carbon and serve as a critical food source for small creatures known as zooplankton, which in turn are consumed by larger animals like fish.\u00a0<\/p>\n But not all oceans are acidifying the same way. Colder locales, like the Arctic or Southern Ocean that encircles Antarctica, more readily acidify than tropical waters. That means the polar regions \u2014 which may be remote but host a bevy of species like whales \u2014 could be approaching a tipping point where organisms aren\u2019t able to build shells. \u201cThe Southern Ocean is about to tip,\u201d said Ken Johnson, a senior scientist who studies the region at the Monterey Bay Aquarium Research Institute but wasn\u2019t involved in the report. \u201cThe water is changing faster. We\u2019re creeping right up to the edge of that tipping point.\u201d<\/p>\n Further complicating matters, planetary boundaries often reinforce one another. In addition to acidification, ocean life is dealing with the breaching of the climate boundary, as the seas have absorbed around 90 percent of the excess heat<\/a> that humans have added to the atmosphere. That\u2019s steadily raised the average ocean temperature<\/a>, but is also driving extreme marine heat waves<\/a>, further stressing the organisms there. (Oxygen concentrations also drop as temperatures rise, compounding their pain.) They\u2019re also dealing with the \u201cintroduction of novel entities\u201d boundary being breached, as chemicals and plastic pollution injure and kill oceanic species<\/a>.\u00a0<\/p>\n Those overlapping crises are not only making it more difficult for organisms to survive, but may also be making it more difficult for the ocean to keep sequestering carbon. That\u2019s what Caesar and her colleagues will be exploring next. \u201cWhat is happening under these different stressors?\u201d Caesar said. \u201cBecause it\u2019s not just ocean acidification. The ocean is also losing oxygen. It\u2019s warming. How is this impacting this ocean buffering capacity?\u201d<\/p>\n The good news is that by rapidly reducing greenhouse gas emissions, we can pull back from the cliff of ocean acidification. In fact, human intervention is why 2 of the 9 planetary boundaries haven\u2019t been crossed. Levels of ozone in the stratosphere are now within safe levels, the report notes, thanks to international agreements banning ozone-depleting substances. And atmospheric aerosols are also within the safe operating space, thanks to countries better regulating the burning of dirty fuels like coal and switching to renewable power like solar and wind.\u00a0<\/p>\n The number of overlapping and reinforcing problems makes the ocean a particular challenge. But by doing things like restoring coastal ecosystems and reducing plastic pollution, humans can reduce the pressures we\u2019re putting on them. \u201cThat can be really hard to tackle, addressing these problems when there isn\u2019t sort of a silver bullet where you change one thing and you fix all the problems,\u201d Rheuban said. \u201cThere\u2019s quite a number of different issues that need to be solved.\u201d<\/p>\n This article originally appeared in Grist<\/a> at https:\/\/grist.org\/oceans\/the-oceans-just-hit-an-ominous-milestone\/<\/a>.<\/p>\n![\"\"](\"https:\/\/www.newsbeep.com\/us\/wp-content\/uploads\/2025\/10\/DJI_0054-1-1024x682.jpg\")
Ocean acidification is intimately intertwined with the planetary boundary of climate change because seawater absorbs carbon dioxide from the atmosphere. (Craig Fujii\/Civil Beat\/2025)<\/p>\n
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