The oceans just hit an ominous milestone

Over the last 12,000 years, Earth has undergone a remarkable transformation, shifting from an ice age to a stable climate that facilitated the dawn of agriculture and human civilization. However, that stability is now threatened as the global population of over 8 billion people accelerates climate change, disrupts ecosystems, and depletes natural resources.

A recent report has highlighted that we have crossed a critical “planetary boundary,” which is a threshold vital for maintaining the Earth’s systems necessary for life. This boundary, linked to the escalating acidification of the oceans, poses serious risks to marine ecosystems, particularly to organisms foundational to the food web. This marks the seventh planetary boundary that humanity has breached out of a total of nine.

Levke Caesar, co-lead of the Planetary Boundaries Science Lab at the Potsdam Institute for Climate Impact Research, and co-author of the report, stated, “What this health check again and again shows is that we have one interlinked, interconnected Earth system. It would be fatal if we only focused on climate change, as there are six other boundaries that have been compromised, all under increasing pressure.”

Planetary boundaries serve as warning signs—imagine a road sign alerting drivers to an upcoming cliff. Crossing one of these boundaries can lead to irreversible changes to the Earth’s systems. For instance, parts of the Amazon rainforest might soon shift to savanna due to combined climate change and deforestation—a potential tipping point. Thus, planetary boundaries act as critical advisories, indicating when a catastrophic shift is approaching.

Consider this analogy: a planetary boundary is like a doctor alerting you to high blood pressure, with the tipping point being a heart attack. “By establishing planetary boundaries, we aim to ensure that while we operate within safe limits, we can avoid tipping points,” Caesar explained.

Prior to including ocean acidification as a formal planetary boundary this year, scientists indicated that six others had already been surpassed: climate change is accelerating, freshwater consumption is unsustainable, species extinction rates are skyrocketing, forests are diminishing, fertilizers are contaminating water supplies, and hazardous chemicals and plastics are seeping into the ecosystem.

Ocean acidification is closely linked to climate change, as oceans absorb carbon dioxide from the atmosphere, which accounts for around 25% of all human CO2 emissions. This chemical reaction forms carbonic acid, resulting in a rise in ocean acidity of 30 to 40% since the beginning of industrialization.

The implications for marine life are alarming. Many species, such as corals, mollusks, and crustaceans, rely on calcium carbonate to form protective shells. However, rising acidity reduces the availability of calcium carbonate, forcing these creatures to work harder to construct and maintain their shells. “Acidification impacts many marine organisms physiologically,” commented Peter Roopnarine, curator of geology at the California Academy of Sciences. “This can affect everything, from respiratory function to skeletal development across the lifespan of these organisms.”

Additionally, rising temperatures and ocean acidification contribute to coral bleaching by stressing corals and causing them to expel the symbiotic algae that provide their energy, further endangering marine biodiversity. As the report confirms, the alarming rise in ocean acidity points to a breach of the planetary boundary concerning ocean health.

This acidification jeopardizes the very foundation of the oceanic food web. Phytoplankton, which absorb CO2 and produce a significant portion of the oxygen in our atmosphere, are essential for ecosystem health. Unfortunately, many phytoplankton species require calcium carbonate for their shells and may struggle to survive amidst the increasing acidity.

Notably, ocean acidification affects different regions unevenly. Colder waters, such as those in the Arctic, are more susceptible to acidification than warm tropical waters. As a result, polar ecosystems, rich in biodiversity, might reach a tipping point in their ability to support shell-building organisms. “The Southern Ocean is rapidly approaching a tipping point,” stated Ken Johnson, a senior scientist at the Monterey Bay Aquarium Research Institute. “The changes are happening at an alarming rate.”

The interplay of various breaching boundaries complicates these challenges. In addition to acidification, oceans have absorbed about 90% of excess atmospheric heat, leading to rising ocean temperatures and extreme marine heatwaves, which further stress marine organisms.

These converging crises make it challenging for organisms to thrive and may impact the ocean’s capacity to sequester carbon. As Caesar and her team plan future research, they aim to understand how these cumulative stressors affect ocean health. “We need to explore the interaction of these stressors,” she remarked. “It’s not just about acidification; the ocean is also losing oxygen and warming. We need to assess how these factors are affecting the ocean’s ability to buffer against climate change.”

There is a silver lining, however: by urgently reducing greenhouse gas emissions, we can mitigate the risks of ocean acidification. Notably, human intervention has already helped two planetary boundaries remain intact; international agreements aimed at phasing out ozone-depleting substances have restored stratospheric ozone levels, and improved regulation of pollution has kept atmospheric aerosols within safe limits.

Despite the multitude of overlapping challenges, solutions exist. Strategies like restoring coastal ecosystems and curbing plastic pollution can significantly ease the pressures on marine environments. “Addressing these interconnected issues is complex because there isn’t a single solution that resolves everything,” cautioned Rheuban. “A multitude of problems requires a multifaceted approach.”