Water temperatures in and around the Great Barrier Reef, Australia, in the past decade have been the warmest in the past 400 years. The results were published recently in Nature. These periods of warming increase the risk of mass coral bleaching and mortality and are likely driven by human-induced climate change. The Great Barrier Reef has undergone a sequence of mass bleaching events in recent years, with the events increasing in frequency since some of the first recorded episodes occurred in the 1980s. Mass coral bleaching can be spurred by warming water temperatures linked to global warming. Analysis of sea surface temperatures in the Coral Sea, which contains the Great Barrier Reef, have until now mainly been limited to recent instrumental observations.
Researchers now reconstructed sea surface temperature data from 1618 to 1995 using coral skeleton samples from within and surrounding the Coral Sea and coupled this dataset with recorded sea surface temperature data from 1900 to 2024. They identified relatively stable temperatures prior to 1900. From 1960–2024, however, they observed an average annual warming for January to March of 0.12 degree C per decade. The average sea surface temperatures for January and March in the mass coral bleaching years of 2016, 2017, 2020, 2022, and 2024 were considerably warmer than in any year in the reconstruction prior to 1900 and were five of the six warmest the region has experienced in the past four centuries. Further modelling suggests that this rate of heating post-1900 can be attributed to human influence.
The authors note there are remaining uncertainties in reconstructed sea surface temperature data due to some of the chemical proportions in the coral that are used to model temperatures being influenced by other variables such as salinity. However, these uncertainties could be reduced with additional sampling of coral cores from the region. The researchers note that even if global warming is kept under the Paris Agreement’s goal of 1.5 degree C above pre-industrial levels, 70% to 90% of corals across the globe could be lost, and that future coral reefs will likely feature a different community structure with less diversity in coral species.
