Oxygen Is Slowly Disappearing, and Most People Haven't Noticed
Dissolved oxygen in the Earth’s oceans, rivers and lakes is disappearing at an alarming rate. Scientists warn that this is not only lethal for aquatic life, but could destabilise the balance of our planet’s systems as a whole. The condition may not recover within a human lifetime.
The findings were published in the journal Limnology and Oceanography in late June and reported by Gizmodo and research institutions including the Scripps Institution of Oceanography at the University of California San Diego.
The decline in dissolved oxygen levels, known as deoxygenation, is driven by three main causes linked to human activity. First, global warming heats the water, reducing its capacity to hold oxygen. Every 1-degree Celsius rise in temperature cuts oxygen storage capacity by roughly 2%.
Second, nutrient pollution from agricultural fertiliser run-off and household waste entering waterways triggers excessive algal growth, which then consumes large amounts of oxygen as it decomposes. Third, changes in water circulation caused by layers of warm surface water prevent oxygen from descending to the seabed.
Lead researcher Erica Ferrer explained that this crisis does not stand alone. “The health and stability of the Earth depends heavily on aquatic ecosystems. If oxygen declines, we disrupt the natural cycles that regulate climate, biodiversity, and even food availability for humans,” she said.
In the study, the scientists propose that aquatic oxygen conditions be added to the list of planetary boundaries — critical limits that must not be exceeded for the Earth to remain habitable.
The decline in oxygen is already interacting closely with other threats such as climate change, ocean acidification and loss of species diversity. Left unchecked, these changes could persist for centuries, even if greenhouse gas emissions were stopped entirely.
The loss of oxygen does not merely kill fish, crabs and other marine animals. The carbon and nitrogen cycles that help cool the planet would be disrupted, accelerating warming. Oxygen-depleted waters actually release greenhouse gases such as methane and nitrous oxide.
Marine mammals that breathe by surfacing for air also suffer as their prey disappears or relocates.
The researchers stress that this does not mean the oceans will run out of oxygen entirely in the near future.
However, the trajectory is already heading towards an unsafe zone, and repairing the damage will take far longer than the time we have left to act.