Coral reef bleaching

Coral reef bleaching in 2016, 2017, and 2020

Mass coral reef bleaching is now common around the world.

Over the summer of 2020, the Great Barrier Reef experienced the most widespread bleaching ever recorded: 60% of its reefs were affected. This is the third mass bleaching in five years: 2016, 2017 and 2020.

(Great Barrier Reef: Most widespread coral bleaching on record: ABC: 7 April 2020)

(We just spent two weeks surveying the Great Barrier Reef. What we saw was an utter tragedy: Australian Geographic: April 2020)

Previous bleaching in 2016 and 2017

Here are two maps of the Australian Great Barrier Reef showing the bleached areas in 2016 and 2017.

A map showing where the Great Barrier Reef bleached in 2016 and 2017
  • In 2016, this giant reef experienced its hottest sea surface temperatures for February, March, and April on record from 1900 to 2016.
  • Eight months after this 2016 marine heatwave, nearly one-third of the entire coral reef had bleached and died.
  • The following year, in 2017, there was another mass bleaching. Successive years of mass bleaching have not been recorded before.

Nearly one-third of the reef is dead after 2016, with more mass bleaching in 2017. This reef destruction is alarming evidence of global warming and the need to reduce greenhouse gases in our atmosphere.

(The Great Barrier Reef is vast. It extends for 2,300 km along the Australian coast.)

Coral reef bleaching records

The Australian Institute of Marine Science has monitored coral reefs since the early 1980s. They have identified 6 mass coral bleaching events due to high ocean temperatures over 38 years. Three of these has been in the last 5 years. The frequency of these mass bleaching events is increasing.

Other threats to the reef

As well as bleaching, the reef also suffers from:

  • Cyclones: The waves break the corals
  • Ocean acidification: the rates at which some corals are now building their skeletons has declined since 1990.
  • Pollution, and
  • The crown of thorns starfish.

The dangers of inaction

This damage is occurring with the current 1°C rise in average global air temperatures above pre-industrial levels. Governments are reacting very slowly, with some negotiating about a 2°C rise. A 2°C rise would almost certainly mean the collapse of warm water tropical reefs around the world.

The Great Barrier Reef and other reefs worldwide will not survive unless there are rapid, deep cuts in greenhouse gas emissions.

On the Great Barrier Reef, we risk losing:

  • The single largest living marine structure on Earth
  • Extraordinary biodiversity
  • A key part of the regional ecosystem.
  • Protection of the Queensland coast from the full force of the Pacific Ocean.
  • A contribution of about $6.4 billion per year to the Australian economy
  • About 64,000 jobs, many in tourism.


Coral Bleaching Events
Australian Institute of Marine Science

Lethal Consequences: Climate Change Impacts of the Great Barrier
The Climate Council 2018

Reef Health: Summer 2018 – 2019
Australian Government: Great Barrier Reef Marine Park Authority

Updated 31 March 2021