Marine heat waves blanketed 96% of the planet’s ocean surface, lasting four times longer than historical averages in what scientists call an unprecedented event.
(CN) — Ocean temperatures soared to record highs in 2023, with marine heat waves — prolonged stretches of unusually warm water — shattering records for intensity, duration and global coverage.
Researchers, in a study published Thursday in the journal Science, suggest these extremes may be more than just another milestone in a warming world. Led by scientists from institutions in China and the United States, researchers raise the possibility that the 2023 marine heat waves could mark a fundamental shift in how the ocean and atmosphere interact.
The findings offer the most comprehensive look yet at a year when vast swaths of ocean turned dangerously warm, threatening marine life and disrupting global weather.
Unlike land-based heat waves, marine heat waves unfold slowly and can persist for months or even years. The North Atlantic event that dominated headlines began in mid-2022 and lasted for 525 consecutive days. In the Southwest Pacific, marine heat waves shattered previous records for both geographic reach and staying power.
When El Niño emerged in the tropical Eastern Pacific, sea surface temperatures spiked 1.63 degrees Celsius, or roughly 34.934 Fahrenheit, above average — an anomaly in oceanographic terms.
The research team, drawing on satellite observations and high-resolution ocean modeling from the ECCO2 project, found that the 2023 marine heat waves lasted four times longer than historical averages. Four regions including the North Atlantic, tropical Eastern Pacific, North Pacific, and Southwest Pacific, accounted for 90% of the excess ocean heating.
The drivers behind these extremes varied by region, researchers found. In some areas, reduced cloud cover allowed more solar radiation to penetrate the ocean’s surface. Weakened winds disrupted typical cooling patterns. Ocean currents shifted in ways that trapped heat rather than dispersing it.
In early August, a particularly ominous milestone was reached: global average sea surface temperatures hit 69.73 degrees Fahrenheit, breaking a record set in 2016, according to NOAA. By year’s end, 2023 had claimed the title of warmest year on record, with global surface temperatures running 2.12 degrees Fahrenheit above the 20th-century average.
For marine ecosystems, the consequences proved severe. Coral reefs, exquisitely sensitive to temperature changes, experienced widespread bleaching events. Mass die-offs struck various species across affected regions.
The fishing industry also felt the economic sting. Abnormally warm waters disrupted fish populations, forcing boats to venture farther from shore or return empty-handed. Along the northeastern United States and Alaskan coasts — where marine heat waves have intensified most dramatically since the 1980s.
Scientists have long known that human-driven climate change is making marine heat waves more frequent and intense. But the 2023 events appeared to cross into new territory, both in their global reach and stubborn persistence.
The study involved 17 researchers from the Eastern Institute of Technology, Southern University of Science and Technology, Scripps Institution of Oceanography, and institutions across China, Thailand, Sweden, France, and the United States. Their analysis relied on multiple data sources, including the ECCO2 ocean modeling project.
For now, the 2023 marine heat waves stand as a reminder of how rapidly ocean conditions can change and how narrow the window may be to prevent more extreme shifts ahead.
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