Earth’s waters are losing oxygen at a pace that scientists say could soon push rivers, lakes and oceans past a point of safe recovery. A new study argues that this decline, known as aquatic deoxygenation, deserves to be treated as a major global warning sign on par with climate change and biodiversity loss.
The research, published in the journal Limnology and Oceanography, was led by Erica M. Ferrer of the University of California, Santa Cruz.
Ferrer and her co-authors build on earlier work calling for aquatic deoxygenation to be added as a tenth “planetary boundary,” a scientific framework used to track the environmental limits that keep the planet livable.
The framework already includes nine categories, such as climate change, ocean acidification and freshwater use, but currently has no formal measure for oxygen loss in water.
Oxygen Levels in Earth’s Waters Are Falling Fast
The study explains that global ocean oxygen levels have dropped by about two percent over the past 50 years, with the steepest losses found near the poles and in parts of the Pacific and Indian Oceans.
More than 200 locations worldwide now experience long-term low-oxygen conditions known as hypoxia. Lakes have been hit hardest, with some losing oxygen at a rate of up to five percent per decade, while rivers are declining more gradually.
The authors point to warming water, agricultural runoff and weaker water circulation as the main drivers behind the trend. Warmer water holds less oxygen, and nutrient pollution from fertilizer and waste feeds algae blooms that consume oxygen as they decompose.
These factors, the study notes, are tightly linked to other global environmental problems, including greenhouse gas emissions and the loss of animal and plant species.
Why recovery from oxygen loss could take centuries
Ferrer’s team also warns that oxygen loss in water is difficult to reverse. Because oceans take centuries to fully circulate, oxygen lost today could remain depleted for generations, even if greenhouse gas emissions were stopped immediately.
The researchers describe a few natural processes that restore oxygen, mainly plant life and atmospheric mixing, and note that engineered fixes such as artificial aeration have shown limited success so far.
The study calls for stronger international attention to the issue, noting that oxygen loss is barely mentioned in major ocean treaties and climate agreements.
The authors suggest that formally recognizing the problem could unlock funding for monitoring programs and conservation efforts, similar to those already in place for climate change and plastic pollution.
While a precise global threshold for safe oxygen levels has not yet been set, the study concludes that current trends already point toward serious, long-term consequences for both wildlife and the humans who depend on healthy waterways.
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