In 2023, scientists report, the world’s oceans experienced the most intense and widespread marine heatwaves ever recorded. Some events persisted for over 500 days and covered nearly the entire globe.
These searing ocean temperatures are causing mass coral bleaching and threatening fisheries, while also signalling deeper, system-wide climate changes. The findings come from the Eastern Institute of Technology, Ningbo, Zhejiang, China.
Data from 2014 to 2016: Mass die-offs
This followed on from earlier, damaging events. A scorching marine heatwave from 2014 to 2016 devastated the Pacific coast, according to University of Victoria researchers, shaking ecosystems from plankton to whales and triggering mass die-offs, migrations, and fishery collapses.
The Canadian researchers synthesised findings from over 300 studies, revealing the far-reaching impacts of rising ocean temperatures. Kelp forests withered, species shifted north, and iconic marine animals perished—offering a chilling preview of the future oceans under climate change.
Between 1925 to 2016, the frequency of marine heatwaves has increased on average by 34% and the length of each heatwave had increased by 17%. Together this led to a 54% increase in the number of marine heatwave days every year.
2023 marine heatwaves: Marking broad changes to our planet’s climate
The 2023 heatwaves were even more impactful. The findings provide insights into the region-specific drivers of these events, linking them to broader changes in the planet’s climate system. They also carry serious economic consequences by disrupting fisheries and aquaculture. More concerningly, for the longer-term picture, these events may also portend an emerging climate tipping point.
Marine heatwaves are intense and prolonged episodes of unusually warm ocean temperatures.
The data was acquired using a mixed-layer heat budget analysis. From the subsequent 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.
New records set
The marine heatwaves 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.
Taking the North Atlantic marine heat wave, which began as early as mid-2022, the researchers show this climate event persisted for 525 days, while the Southwest Pacific event broke prior records with its vast spatial extent and prolonged duration. Moreover, in the Tropical Eastern Pacific, temperature anomalies peaked at 1.63 degrees Celsius during the onset of El Niño (Southern Oscillation).
Major change?
According to the researchers, the 2023 marine heatwaves 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.
The research appears in the journal Science, titled “Record-breaking 2023 marine heatwaves.”
These sweeping events should stand as calls for urgent action in marine conservation and climate mitigation.
