Ocean temperatures hit record highs in historic 2023

Ocean temperatures soared to unprecedented levels in 2023, with marine heatwaves shattering records for intensity, duration and global coverage, according to a comprehensive study published Thursday in the journal Science. The findings suggest these extreme oceanic events may signal a climate tipping point that could trigger irreversible changes to marine ecosystems worldwide.

Scientists found that marine heatwaves in 2023 set new records across multiple metrics, lasting four times longer than historical averages and affecting 96% of the global ocean surface. The North Atlantic experienced the most prolonged marine heatwave on record, persisting for 525 days after beginning in mid-2022. In the Southwest Pacific, heatwaves broke previous records for both geographic extent and duration, while the Tropical Eastern Pacific saw temperature anomalies peak at 1.63 degrees Celsius during El Niño onset.

Global Scale of Ocean Warming

The 2023 marine heatwaves represented "a global event with a 50-year return period, with a less than two percent chance of occurrence," according to researchers from China and the United States. Four key regions—the North Atlantic, Tropical Eastern Pacific, North Pacific, and Southwest Pacific—collectively accounted for 90% of global oceanic heating anomalies. 

Global average sea surface temperatures hit 69.73 degrees Fahrenheit in early August, breaking a record set in 2016. By year's end, 2023 had claimed the title of warmest year on record globally, with surface temperatures running 2.12 degrees Fahrenheit above the 20th-century average.

Climate Tipping Point Concerns

The unprecedented scale and persistence of 2023's marine heatwaves has prompted researchers to warn of a potential climate tipping point. "While a full ocean-climate system collapse has not occurred, irreversible impacts—mass coral bleaching in tropical reefs, collapse of key habitats—are already emerging," said lead author Tianyun Dong from China's Eastern Institute of Technology.

The researchers suggest the 2023 events "may mark a fundamental shift in ocean-atmosphere dynamics, potentially serving as an early warning of an approaching tipping point in Earth's climate system". However, some experts caution against drawing definitive conclusions. Michael McPhaden, a senior scientist at NOAA who was not involved with the study, told Live Science: "I don't consider 2023 to be a tipping point," noting that natural variability from El Niño events also affects oceanic measurements.

Economic and Ecosystem Impacts

The marine heatwaves caused widespread ecological and economic disruption. Coral reefs experienced mass bleaching events, while fish populations shifted dramatically, forcing commercial vessels to venture farther from shore or return empty-handed. The combined effect of extreme heat and associated drought caused $14.5 billion in economic losses in North America alone, making it the costliest weather and climate disaster of 2023.

The research team used satellite observations and ocean reanalysis data to identify diverse regional drivers behind the extreme events, including increased solar radiation due to reduced cloud cover, weakened winds, and ocean current anomalies. These findings highlight the complex interplay of factors that can amplify marine heatwaves beyond what climate models typically predict.