Ocean Warming and Dive Destinations

The Ocean as Heat Absorber

The ocean has absorbed approximately 90% of the excess heat trapped by atmospheric greenhouse gases since the Industrial Revolution. This has buffered land surface warming — without the ocean's heat absorption, atmospheric temperatures would have risen far faster — but at a profound cost to marine ecosystems.

Global average sea surface temperature has risen by approximately 0.13 degrees C per decade since 1980. The figure understates regional variation: parts of the North Atlantic have warmed at rates two to three times the global average; the Arctic Ocean is warming at nearly four times the global rate.

Changes Divers Are Observing

Species range shifts: Tropical fish species are appearing at higher latitudes as water temperatures warm poleward. In the Mediterranean, pufferfish (Lagocephalus sceleratus), lionfish, and barracuda species that were previously rare or absent are now established in the eastern basin. Off the coasts of Japan and southern Australia, coral species are colonizing rocky substrates that were historically too cold.

Seasonal changes: Whale shark aggregations, manta ray cleaning station activity, and shark breeding seasonal timing are all influenced by water temperature. Operators in multiple destinations have noted aggregations arriving later in the season or becoming less predictable as the temperature signals that coordinate these behaviors shift.

Coral bleaching frequency: As documented elsewhere, bleaching events that were once separated by decades of recovery now occur at intervals too short for recovery — annual or near-annual bleaching in the most affected regions.

Jellyfish proliferation: Warming, combined with reduced predation from overfished predators, is associated with jellyfish population explosions in multiple ocean basins. In the Mediterranean and the North Sea, jellyfish blooms have become significantly larger and more frequent since the 1990s.

The Destinations Most at Risk

The Maldives: At 1.2 metres average elevation above sea level, the Maldives faces existential risk from sea level rise alongside reef degradation from warming. The reefs that make the Maldives a dive destination are already experiencing bleaching on the frequency predicted for 1.5 degrees C scenarios.

Coral Triangle reefs: The Indonesian, Philippine, and PNG reefs at the heart of global marine biodiversity are subject to both thermal bleaching and ocean acidification. Their exceptional biodiversity provides some resilience, but the scale of warming projected under current trajectories exceeds the adaptation capacity of existing reef ecosystems.

The Great Barrier Reef: The 2024 bleaching event was the sixth in nine years and the most extensive on record. The reef's future under current warming scenarios involves extensive restructuring of species composition — more thermally-tolerant species persist while sensitive species are lost.