Coral reef bleaching

Coral reef bleaching in 2016 and 2017

Mass coral reef bleaching is now common around the world.  Here two maps of the Australian Great Barrier Reef showing the areas of that were hit in 2016 and 2017.

A map showing where the Great Barrier Reef bleached in 2016 and 2017
  • In 2016, this giant reef recorded its hottest sea surface temperatures for February, March, and April since records began in 1900.
  • Eight months after this 2016 marine heat wave, 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 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 mass coral bleaching events due to:

  • High ocean temperatures:  We are seeing more marine heat waves as our planet and oceans warm, and
  • Extreme rainfall events which increase levels of fresh water over reefs and lead to bleaching. We are seeing more extreme rainfall events as a warmer atmosphere can hold more moisture.

The Institute reports mass bleaching events in:

YearBleaching due to
2008Fresh water
2011Fresh water
2016 Temperature
2017 Temperature

The frequency of these mass bleaching events is clearly 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

The damage we are seeing now 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 around the globe will not survive unless there are very 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