Marine heatwaves are catastrophic impacts of climate change many of us are already familiar with. But how much do they cost society?
During marine heatwaves, ocean temperatures can become so high that many species become stressed, or die. Critical coastal habitats, such as seagrass meadows, corals and kelp forests, can die out, limiting their natural capacity to store carbon dioxide and disrupting fisheries and tourism.
Until now, we’ve not understood how much society loses during marine heatwaves. This is what our new research, published in Science, sought to find out.
We looked at 34 marine heatwaves worldwide, and found one event in 2016 in southern Chile cost more than US$800 million (A$1.07 billion) in direct losses to aquaculture (cultivating aquatic plants and animals for food). Another heatwave in Shark Bay, Western Australia, resulted in US$3.1 billion (A$4.14 billion) per year in indirect losses, as a result of lost carbon storage when seagrass beds were impacted.
As world leaders prepare to meet for COP26 in Glasgow, they must keep these intensifying marine heatwaves front of mind. They are not only a stress test for the ocean’s ecosystems, but also for millions of people who rely on them – and who are already suffering.
Marine heatwaves can strike anywhere
Marine heatwaves are defined as prolonged periods of very warm surface water temperatures that commonly last for weeks to months. Climate change has caused surface waters to warm at an average rate of 0.15℃ per decade over the past 40 years, leading to longer and more frequent heatwaves. Eight of the ten most severe events ever recorded took place in the past decade alone.
They can occur in any ocean for two reasons: heat entering the ocean via the atmosphere, or via ocean currents that bring warmer waters. When both processes occur together, they lead to heatwaves with even higher temperatures.
Heatwaves lead to major economic losses because they modify the ocean’s “ecosystem services” – the range of benefits healthy marine ecosystems provide to humans.
For example, fishers, aquaculturalists, and tourism operators all rely on “foundation” species – such as corals, kelps and seagrasses – because they provide habitat for a range of creatures.
When a marine heatwave destroys a foundation species, like we’ve seen in the recent, back-to-back coral bleaching events in Australia’s Great Barrier Reef, then the whole ecosystem suffers, and the knock-on socio-economic consequences can run into billions of dollars.