Record-breaking sea surface temperatures

This year’s mass coral bleaching on the Great Barrier Reef was triggered by record-breaking sea surface temperatures.

The rising temperatures reflect the underlying trend of global ocean warming caused by climate change.

A strong El Niño also resulted in little monsoon activity and, as a consequence, long periods without cloud cover which would typically have offered corals some respite from heat stress.

According to the Australian Bureau of Meteorology, the Great Barrier Reef recorded its hottest-ever average sea surface temperatures for February, March and April since records began in 1900.

Map showing ocean temperatures around much of Australia were either above average or the highest on record.

Above: Highest on record refers to highest sea surface temperature value since 1900. Decile 10 is the highest 10 percent of records — this category is 'very much above average'. Analysis supplied by the Bureau of Meteorology. Based on the ERSST v4 dataset produced by the National Oceanic and Atmospheric Administration. © Australian Bureau of Meteorology

February 2016

In February 2016, the average sea surface temperature over the Great Barrier Reef was 1.1 degrees higher than the 1961–1990 average.

Further information on graphs is available from the Bureau of Meteorology.

Bar graph of sea surface temperature anomalies for February between 1900 and 2016

© Australian Bureau of Meteorology.

March 2016


In March 2016, the average sea surface temperature over the Great Barrier Reef was 1.3 degrees higher than the 1961–1990 average.

Sea surface temperature anomalies for March between 1900 and 2016

© Australian Bureau of Meteorology.

April 2016

In April 2016, the average sea surface temperature over the Great Barrier Reef was one degree higher than the 1961–1990 average.

Bar graph showing sea surface temperature anamolies for April between 1900 and 2016

© Australian Bureau of Meteorology.

Heat stress patterns

The heat stress was not uniform across the Reef over the hottest period of the year, between December 2015 and March 2016.

The below map shows how heat accumulated over the Reef by the end of March, increasing the risk of coral bleaching.

Local weather patterns, including rain and heavy cloud from ex-cyclone Winston, meant the intensity of coral bleaching in each region varied.

Map of Great Barrier Reef coastline showing heat stress was not uniform across the Reef over summer

Above: The scale used is an indicator of coral bleaching risk. One degree heating day (DHD) is one degree above the long-term average temperature for one day.