In 2025, Earth’s oceans reached their highest temperatures since record-keeping began, establishing a worrisome new milestone.
Research published Friday in a peer-reviewed journal revealed that the upper 2,000 meters (6,561 feet) of the ocean absorbed an unprecedented 23 zettajoules more energy than in 2024—equivalent to roughly 37 times the world’s total energy consumption in 2023.
The investigation focused on ocean heat content, which tracks the amount of surplus thermal energy stored in global oceans over time. Monitoring ocean temperatures serves as a crucial method for scientists to observe long-term climate shifts, as oceans regulate the effects of atmospheric carbon emissions by absorbing roughly 90% of the extra heat captured by greenhouse gases.
Scientists also observed that 2025’s global average sea-surface temperatures—the interface between ocean water and atmosphere—ranked as the third highest ever recorded, staying approximately 0.5°C (1°F) above the 1981-2010 baseline. Certain regions warmed more rapidly than others, with the South Atlantic, North Pacific, and Southern Ocean showing the most pronounced increases.
Escalating ocean temperatures trigger numerous climate consequences. Hotter oceans drive sea-level rise (partly from thermal expansion of water) and intensify extreme weather events. This encompasses strengthening hurricanes while slowing their forward motion, causing storms to stall longer over land and potentially inflict greater damage. These effects are already evident—last year marked only the second time on record that the Atlantic basin produced at least three Category 5 hurricanes.
Increasing ocean heat also accelerates coral reef degradation, which undermines fisheries and coastal protection against storm surges and rising seas. A 2025 study determined that tropical coral reefs are crossing critical thresholds, with 80% suffering from extreme heat waves, bleaching incidents, and mass mortality.
The current findings sound urgent warnings about the climate repercussions facing the world from ocean warming. The researchers emphasize that without worldwide action to cut emissions, temperatures will keep climbing.