The article discusses the effects of human-induced global warming on ocean ecosystems, specifically focusing on the increasing frequency and intensity of marine heatwaves. These heatwaves cause significant damage to coral reefs and other marine life, as seen in the 2015-2016 event in Western Australia which caused widespread coral bleaching.
While the increase in global temperature is gradual, marine heatwaves cause rapid and drastic temperature increases, reaching over 7 degrees Celsius above average and lasting for weeks. The article highlights the current lack of a reliable alarm system for these heatwaves, as their causes are not fully understood. One suggested cause is abnormal air pressure, as evidenced by the 2019 Northeast Pacific heatwave caused by weaker-than-normal air pressure. Research is ongoing to understand the causes of both surface and subsurface heatwaves.
The article concludes by questioning the survival of marine ecosystems, using the popular cartoon character SpongeBob as a metaphor. Even if certain species survive, the state of their ecosystems will likely be severely altered. Key points raised include:
Born and raised inland, my childhood imagination for oceans primarily came from the popular animated TV series SpongeBob SquarePants. The series took place in an underwater city, and thanks to its creator who was an actual marine scientist, we could see a variety of vivid marine creatures in cartoon. Even till today, this is still one of my favorite TV shows.
Therefore, I felt so sorry for my lovely underwater friends when I had to study ocean warming, during my PhD.
Will SpongeBob and his friends survive in global warming? Human-induced warming increases at a rate of 0.2 Celsius degrees (about 0.4 F) per decade (Ref 1), which does not sound too horrible since we hardly sense such a tiny difference. But the problem is that these small increases contribute to more frequent extreme weather, both for the atmosphere and the ocean. Given the unbearable scorching days we experienced over the past few summers, how are the marine creatures doing now?
Not good, actually. Extreme weather events can rapidly cause disastrous repercussions for a local ecosystem. Nevertheless, they are particularly hard to capture or predict in computer simulations. For marine creatures, what bothers them nowadays is this extreme phenomenon known as marine heatwaves, which refers to localized, exceedingly warm ocean water. When marine heatwaves occur, the temperature can rise over 7 Celsius degrees above average and last for weeks. This sounds much more horrible than 0.2 C per decade, right? While humans use air conditioners to avoid heatwaves, coral reefs have nowhere to escape, which is disastrous. For example, the marine heatwave in 2015–2016, resulted in 56.6–80.6% bleaching in Kimberley, a beautiful coast in the northwest of Western Australia. And it was not the only affected region — this event wreaked serious havoc on coral reefs around the world, becoming the third global mass bleaching event. (Ref 2) You can never overstate the importance of coral reefs in terms of how many marine species thrive on them.
However, research on marine heatwave are still in the initial stages. We do not clearly know why marine heatwaves happen and therefore lack an effective alarm system. Some suggest that they are triggered by abnormal air pressure. The notorious marine heatwave over the Northeast Pacific in summer 2019 was primarily caused by an observed weaker-than-normal air pressure over the North Pacific. This unusual factor lasted for so long that it managed to alter the wind, cloud, and ocean temperature, and led to this warm water patch as a consequence. (Ref 3) This study offered valuable insights into how marine heatwaves occur, but more work is in order before we fully understand this phenomenon. For one thing, studying on one regional case is not enough and we are looking for comprehensive explanations for global marine heatwaves; for another thing, surface warming is the tip of the iceberg — subsurface marine heatwaves can have more severe impacts on ecosystems. Admittedly, subsurface study is more difficult due to limited observation, but it is crucial in particular that a large part of extreme events do not have any clues on the surface.
So, back to the beginning question: will SpongeBob survive in global warming? It is hard to say — you may argue that SpongeBob is a kitchen sponge rather than a sea sponge. But there is no doubt that marine ecosystem has been impaired. Even if SpongeBob survives, his homeland will look much different.
And, we will lose a fantastic underwater story.
References:
Forster, P. M., et al. Indicators of Global Climate Change 2022: annual update of large-scale indicators of the state of the climate system and human influence, Earth Syst. Sci. Data, 15, 2295–2327, https://doi.org/10.5194/essd-15-2295-2023, 2023.
Le Nohaïc, M. et al. Marine heatwave causes unprecedented regional mass bleaching of thermally resistant corals in northwestern Australia. Sci Rep 7, 14999 (2017). https://doi.org/10.1038/s41598-017-14794-y
Amaya, D.J. et al. Physical drivers of the summer 2019 North Pacific marine heatwave. Nat Commun 11, 1903 (2020). https://doi.org/10.1038/s41467-020-15820-w
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