Marine heatwaves have doubled in frequency over the last 35 years and this is only going to get worse, warn scientists in a new paper published in the journal Nature. Paris targets won’t save us, says a team of scientists, as even a warming of 2°C will lead to increased heat waves frequency, duration and strength.
Over the last decades, marine heatwaves have received much less attention from scientists than terrestrial ones. Their impacts are, however, no less severe. Lasting for weeks and even months, they have shattered commercial fishing in Australia, led to the closure of crab fishes in California, and can even accelerate the current rate of climate change.
Heatwaves are also dangerous to marine life, causing deaths of sea lions, whales and other sea animals that are not used to wild swings in temperatures in their habitats. And while lobster and some other free-swimming animals might adapt quite well, this will not happen to all the animals affected.
Coral reefs, which are home to one fourth of all marine species, are particularly vulnerable to hot spells. Recently 29% of the coral reefs from Australia’s Great Barrier Reef have been impacted by unexpected temperature spikes, resulting in the massive bleaching of corals.
“Until now, the corals were often able to recover from such bleaching events,” says Thomas Frolicher a lead-author of the paper. However, if those events become more frequent and durable, the ability of coral reefs to regenerate might collapse. This, in turn, can lead to shifts in ecosystem functioning, much less favorable to life.
Researchers used satellite records and climate models to find changes in marine heatwaves. They looked into two possible futures. Under the “business-as-usual” scenario average global air temperature heat up 2°C by 2100, while the second one precludes 2°C warming.
With 33 marine heatwaves a year today, twice as many as there were in 1982, we are going to see the number jump to an estimated 84 under a 2°C increase scenario, and to 150 under a 3.5°C scenario. The changes will also concern the areas of marine heatwaves. Already risen by three times, it will increase nine-fold on a planet with 2°C warmer average temperatures and 21-fold under the 3.5°C increase scenario. The length of heatwaves is also going to change. Today one heatwave lasts 25 days on average, but there is a risk they will become twice or even four times longer than now.
Finally, heatwaves also might damage ecosystems at the ocean surface, which store vast amounts of carbon dioxide, thereby leading to its unintentional release. This would further accelerate global warming and make matters even worse. These results signal an urgent need for increased environmental protection and adaptation efforts towards the marine ecosystems we have still left today.