Oceans

No marine heat waves occurred, but the
Great Barrier Reef remained in poor condition.

Oceans absorb 93% of excess heat from climate change. Unlike atmospheric heat content, global ocean heat content was slightly (1%) less than in 2019.

Global sea level rose by 4.3 mm, marking an increase of 76 mm since 2000 and 98 mm since 1993.

Sea level around Australia has been rising faster than the global average. The fastest rate of rise was in the Tasman Sea, which has risen by more than 150 mm since 1992.

Australian ocean surface temperature increased and was the equal fourth warmest year on record. Mean temperature was 0.17°C above the 2000– 2019 average and 0.32°C above the 1961- 1990 average.

High temperatures in the tropical seas culminated in a marine heatwave in the Great Barrier Reef in February-March, which experienced the hottest temperatures since at least 1955. 

The marine heatwave caused the third mass bleaching event in the Great Barrier Reef in five years, following events in 2016 and 2017. There was severe bleaching of 25% of reefs and unlike previous events the southern reef was also affected. Overall reef condition was already poor and did not change substantially from 2019.

Maximum monthly sea surface temperature across the GBR (BoM)
Maximum monthly sea surface temperature across the GBR (BoM)