Picture: Great Barrier Reef. Credit: Francesco Ungaro.

Thermal coral bleaching events over the Pacific, including those over the Great Barrier Reef, have commonly been linked to the El Niño–Southern Oscillation, with bleaching reported to be a direct result of warmer sea surface temperatures driven by El Niño (the positive phase of El Niño–Southern Oscillation).

However, coral bleaching events have also been reported over the Great Barrier Reef during La Niña events and the neutral phase of the El Niño–Southern Oscillation, when large-scale sea-surface temperatures may be cooler than normal.

CLEX researchers and colleagues have found that the sea-surface temperature anomaly over the Great Barrier Reef is more highly correlated with local cloud cover than with El Niño Southern Oscillation. This significant relationship between local cloud cover and sea-surface temperatures can be found over two-thirds of the study domain even when the El Niño Southern Oscillation impact is ignored.

This indicates that local-scale reduced cloud cover plays an important role in regional warming of the shallow water over the Great Barrier Reef, regardless of the large-scale El Niño Southern Oscillation impact.

Paper: Zhao, W., Huang, Y., Siems, S., & Manton, M. (2021). The role of clouds in coral bleaching events over the Great Barrier Reef. Geophysical Research Letters, 48, e2021GL093936. https://doi.org/10.1029/2021GL093936