Scientists are sounding the alarm. Coral bleaching is happening worldwide. Today, a team reveals that behind this phenomenon lies a possibly even more concerning process.
2023 was the hottest year on record, both on land and in the oceans. It was also the worst year ever observed for coral bleaching in the northern hemisphere. Scientists expected the southern hemisphere to follow the same trend in early 2024, which has indeed happened. No region on Earth has been spared.
It is important to remember that coral reefs, the most vulnerable of all ecosystems, began bleaching and dying due to high temperatures as early as the 1980s. Those that still survive today are finding it increasingly difficult to withstand the warming.
From Coral Bleaching to Warming Ocean Currents
Researchers from the Global Coral Reef Alliance studied the phenomenon using satellite data, spatial models, temporal trends, and in-situ observations. They focused on what they call hotspots, areas where the average temperature is 1°C higher than the warmest month. Hotspots for coral bleaching.
In an article published in the Oxford Open Climate Change journal, they reveal how the massive coral bleaching actually hides an extreme warming of the main warm ocean currents in 2023. This suggests that the transport of heat from the tropics to the polar regions accelerated last year, while the mixing with cold deep waters slowed down, keeping the tropics relatively cool and overheating the subpolar regions.
Behind Coral Bleaching, a Changing Ocean
As a result of these large-scale ongoing changes in ocean circulation, polar ice melting is accelerating, as is ocean stratification. All this is happening even though these major climate warming feedbacks are not taken into account by the projections of the Intergovernmental Panel on Climate Change (IPCC).