In warm water: Climate change, marine heat waves and coral bleaching | Report

2021 has been the warmest year on record for the world’s oceans. Climate change is warming the ocean, leading to more frequent and severe marine heat waves. Over the past year, the excess heat absorbed by the ocean was equivalent to seven Hiroshima atomic bombs exploding every second.

In the past six years alone, marine heat waves have caused three episodes of massive bleaching on the reef. If climate change continues unabated, the reef could face bleaching conditions every year after 2044. These conditions would effectively destroy the reef and most of the world’s shallow water tropical reefs.

More frequent and severe marine heat waves also have devastating consequences for other marine ecosystems. Over the past decade, marine heatwaves have caused mass kills of key species along 45% of Australia’s coastline – including corals, kelp, seagrass and mangroves.

But every fraction of a degree of warming avoided will be measured in the ecosystems saved. Reduce global emissions by at least 50% this decade is key to the survival of Australia’s ocean wonders, which are of natural, social, cultural and international significance.

After a summer of marine heat waves, the reef is again at risk of massive bleaching. Sea surface temperatures are above average over most of the reef – up to 3°C warmer in the central parts of the reef. Weak to moderate bleaching is already underway, with the worst affected corals near Townsville.

To avert climate catastrophe and best protect the Great Barrier Reef, governments must commit to immediate, deep and sustained emission reductions this decade.

A net zero goal by 2050 – regardless of the fact that the Liberal-National government has no credible plan to achieve it – is not enough. The Climate Council is calling on Australia to cut its emissions by 75% below 2005 levels by 2030. As a first step, the federal government should join forces with key allies and commit to halving emissions during this decade.

Teresa H. Sadler