The water temperatures in and around the Great Barrier Reef of Australia in the last decade were the warmer in 400 yearsaccording to research published in the journal Nature.

Corals are sensitive to heat stress, and these periods of warming increase the risk of mass bleaching and mortality of corals, likely due to anthropogenic climate change. Already the Great Barrier Reef, one UNESCO World Heritage Sitehas experienced a series of mass bleaching events in recent years, and the events have been increasing in frequency since the first recorded episodes in the 1980s.

In the current research, the scientists reconstructed sea surface temperature data from 1618 to 1995, using samples of coral skeletons from the Coral Sea, in which the Great Barrier Reef is located. They then combined this data set with recorded sea surface temperature data from 1900 to 2024.

The researchers found relatively stable temperatures before 1900, but from 1960 to 2024 they observed an average annual increase in January to March temperatures of 0.12 degrees Celsius per decade.

They note that average sea surface temperatures for January and March during the mass coral bleaching years 2016, 2017, 2020, 2022 and 2024 were significantly higher than in any year of the pre-1900 reconstruction and were five of the six warmest years the region has experienced in the past four centuries.

Further modeling shows that this rate of warming after 1900 can be attributed to human influence.

The researchers note that there are still some uncertainties in the SST reconstruction data because some of the chemical ratios in coral used to model temperatures are also affected by other variables. However, these uncertainties could be reduced by additional sampling of coral cores from the area.