The Ocean's Health Is Deteriorating on Multiple Fronts, U.N. Scientists Warn

The world’s oceans are facing a “deepening crisis” as a number of stressors, including climate change, pollution, overfishing, and biodiversity loss put a strain on ocean systems, according to a new United Nations assessment. 

The report, which contains contributions from nearly 600 scientists from 86 countries, examines the ocean’s health from 2021 to 2025, and is the third World Ocean Assessment since 2015. It documents the cumulative impact of human activity on our oceans—especially in recent years. 

Sea levels are continuing to rise at an increasing rate, more than doubling from 2mm a year prior to 2015 to 4.3mm a year in 2023, the report finds. Approximately 16% of the total increase in ocean heat content since 1955 has occurred since 2018—with the greatest relative warming observed in the Atlantic Ocean and the southern parts of the Indian and Pacific Oceans. 

“Climate change stands out as the most significant driver. It is causing rising temperatures, sea level rise, acidification, de-oxygenation, as well as increasing frequency and intensity of extreme events, such as marine heat waves,” Rafael González-Quirós, director of the Oceanographic Centre of Gijón and joint coordinator of the group of experts of the third cycle of the U.N. Regular Process, said at a press conference. According to the report, it has already absorbed 90% of the excess heat and 30% of the carbon dioxide released into the atmosphere by the burning of fossil fuels, contributing to ocean warming. 

Plastics also emerged as a major threat to ocean health. An estimated 52.1 million metric tons of plastic waste is produced every year. Much of it is discharged into the ocean each year, hard to recover, and impacting thousands of marine species. 

Oceans cover 70% of the planet, and play a central role in regulating the climate. Yet increased environmental impacts come while much of the ocean remains unknown to us—only 27% of the ocean floor is mapped, and deep-sea ecosystems are poorly understood, the report notes. 

“Little of the vulnerability of marine biodiversity, species genetics, and microbial communities, particularly in the deep sea, to climate change and emerging economic activities is understood,” the report says. 

However, climate change has already had a devastating impact on species habitats, particularly along coastlines, according to the report. Coral reefs, for example, are passing their planetary tipping point, a threshold that, once crossed, leads to large, accelerating, and often irreversible changes.

In one bright spot, the report highlighted impactful efforts in ocean preservation. The landmark High Seas Treaty, which came into effect earlier this year, put in place international rules to protect the two-thirds of the global ocean that lies outside any country’s jurisdiction. It, along with more than 50 other ocean protection treaties, have helped protect biodiversity and manage resources. 

Yet the report highlighted a “fragmentation” when it comes to global ocean governance—a trend that was visible earlier this month, when the Trump Administration announced its plans to dismantle a deep-ocean observation system that monitors coastal environments, marine ecosystems, and currents. The data has long been used to understand oceanic and climate trends like how the ocean is absorbing greenhouse gases from the atmosphere or the impact of marine heat waves. Days after, the European Union pledged to boost its own monitoring systems.