Record Ocean Heat in 2025 Brings Huge Economic Costs

Two fishermen in their boat in Rincao, Cabo Verde.

In 2025, global ocean temperatures rose to some of the highest levels ever recorded, signalling a continued accumulation of heat within the Earth’s climate system and raising deep concern among climate scientists. The economic toll of ocean-related impacts—including collapsing fisheries, widespread coral reef degradation, and mounting damage to coastal infrastructure—is now estimated to be nearly double the global cost of carbon emissions, placing immense strain on economies and endangering millions of lives.

On January 14, the World Meteorological Organization (WMO) confirmed that global temperatures have reached record highs over the past 11 years, with ocean heating continuing at an alarming pace. Despite the cooling influence of La Niña, 2025 became the third-hottest year ever recorded. In just the past year, ocean temperatures increased by an estimated 23 ± 8 zettajoules—roughly equivalent to 200 times the world’s total electricity generation in 2024.

With an estimated 90 percent of excess heat from global warming absorbed by the world’s oceans, rising ocean temperatures have become one of the clearest indicators of the accelerating climate crisis, carrying profound risks for ecosystems and human life. The ocean is central to global prosperity, supporting livelihoods, market economies, and overall human well-being.

“Global warming is ocean warming,” said John Abraham, a professor of thermal science at the University of St. Thomas. “If you want to know how much the Earth has warmed, or how fast it will warm in the future, the answer is in the oceans.”

Zeke Hausfather, a climatologist and research scientist at the University of California, Berkeley, described the ocean as the “most reliable thermostat of the planet.”

According to WMO figures, roughly 33 percent of the Earth’s total ocean area ranked among the three warmest conditions for ocean ecosystems on record, while about 57 percent fell within the top five. These regions include the tropical and South Atlantic Ocean, the Mediterranean Sea, the North Indian Ocean, and the Southern Ocean.

The primary impact of human-generated carbon dioxide emissions on the ocean is rapid warming, which significantly reduces the ocean’s capacity to hold oxygen—a critical lifeline for marine species. Rising temperatures also accelerate ocean acidification, weakening marine organisms, disrupting ecosystems, altering species physiology, and triggering mass die-offs.

These effects have catastrophic consequences for biodiversity, fuelling widespread coral reef bleaching, the collapse of seagrass beds, and the decline of kelp forests. Rising ocean temperatures also intensify extreme weather events and accelerate sea-level rise, increasing coastal flooding, erosion, and displacement—placing millions of people, particularly in low-lying coastal communities, at heightened risk.

While some ocean-based benefits—such as seafood and maritime transport—are reflected in market prices, many others, including coastal protection, recreation, and marine biodiversity, remain overlooked. These losses form part of the invisible social “blue cost” of carbon emissions, despite their essential role in linking oceans, people, and economic systems.

“If we don’t put a price tag on the harm that climate change causes to the ocean, it will remain invisible to key decision-makers,” said environmental economist Bernardo Bastien-Olvera, who led a Scripps Institution of Oceanography study at the University of California, San Diego.

“Until now, many ocean-related variables lacked market value and were excluded from economic calculations. This study is the first to assign monetary-equivalent values to these overlooked impacts,” he added.

The study found that accounting for ocean-related social costs nearly doubles the estimated global cost of carbon emissions. Without ocean impacts included, the average cost per ton of carbon dioxide was about USD 51. When ocean losses were factored in, the cost rose by an additional USD 41.6 per ton, reaching USD 97.2—a 91 percent increase.

With the WMO Global Carbon Budget estimating global carbon dioxide emissions at around 41.6 billion tons in 2024, this translates into nearly USD 2 trillion in ocean-related losses in a single year—costs that are largely absent from standard climate assessments. The study also found that market damages from ocean degradation could reach USD 1.66 trillion annually by 2100.

In addition, non-use values—such as recreational benefits—now amount to an estimated USD 224 billion annually, while non-market impacts, including nutritional losses from collapsing fisheries, add another USD 182 billion each year. Many of these losses, Bastien-Olvera noted, are cultural and societal in nature and carry deeper significance for affected communities.

“When an industry emits a ton of carbon dioxide, society pays the price. This figure allows companies to assess the real damage their emissions cause through cost-benefit analysis,” he said.

In response to accelerating ocean warming, governments, scientists, and international organisations are advancing strategies to reduce emissions and protect marine ecosystems. These include expanding renewable energy, strengthening marine monitoring systems, and pursuing large-scale ecosystem restoration.

The United Nations has renewed pressure on countries to meet Paris Agreement commitments, while initiatives such as the Global Ocean Observing System and the High Seas Treaty aim to improve ocean protection and governance.

Scientists are also testing experimental approaches to counter climate-driven ocean changes. In late 2025, marine scientist Adam Subhas and his team released 16,200 gallons of sodium hydroxide into the ocean to neutralise rising acidity levels. Though controversial and still experimental, the effort reflects growing interest in unconventional climate interventions.

“As long as the Earth continues to accumulate heat, ocean heat content will keep rising and records will continue to fall,” Abraham said. “The biggest uncertainty is human action. Together, we can reduce emissions and safeguard a future in which people and ecosystems can thrive."