The oceans are overheating—and scientists say a climate tipping point may be here

These events pose severe threats to marine ecosystems, often resulting in widespread coral bleaching and mass mortality events. They also carry serious economic consequences by disrupting fisheries and aquaculture. It’s widely understood that human-driven climate change is driving a rapid increase in the frequency and intensity of MHWs.

In 2023, regions across the globe, including the North Atlantic, Tropical Pacific, South Pacific, and North Pacific, experienced extreme MHWs. However, the causes underlying the onset, persistence, and intensification of widespread MHWs remain poorly understood.

To better understand the MHWs of 2023, Tianyun Dong and colleagues conducted a global analysis using combined satellite observations and ocean reanalysis data, including those from the ECCO2 (Estimating the Circulation and Climate of the Ocean-Phase II) high-resolution project.

According to the findings, MHWs of 2023 set new records for intensity, duration, and geographic extent, lasting four times the historical average and covering 96% of the global ocean surface. Regionally, the most intense warming occurred in the North Atlantic, Tropical Eastern Pacific, North Pacific, and Southwest Pacific, collectively accounting for 90% of the oceanic heating anomalies.

The researchers show that the North Atlantic MHW, which began as early as mid-2022, persisted for 525 days, while the Southwest Pacific event broke prior records with its vast spatial extent and prolonged duration. What’s more, in the Tropical Eastern Pacific, temperature anomalies peaked at 1.63 degrees Celsius during the onset of El Niño.

Using a mixed-layer heat budget analysis, the scientists discovered diverse regional drivers contributing to the formation and persistence of these events, including increased solar radiation due to reduced cloud cover, weakened winds, and ocean current anomalies. According to the researchers, the 2023 MHWs 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.