Earth Chat

Marine heatwave threatening life below water




With last month being the hottest October on record, 2023 is on track to be the warmest year in history.[1]As the Earth's climate continues to warm, we are witnessing a range of consequences that are affecting both the environment and human livelihoods.

Coastal communities are increasingly being exposed to climate change-driven extreme weather events and rising temperatures. Around 3.6 million people live in areas that are vulnerable to these climate impacts.[2]The arrival of El Nino further amplifies these effects, leading to extreme heatwaves breaking temperature records worldwide.[3]Heatwaves are not confined to land; the ocean is also exposed to these extreme temperatures.

The average ocean surface temperature broke record levels in August, reaching almost 21°C.[4]In some areas, such as the Florida Keys, water temperatures even exceeded 38°C at one point–as hot as a hot tub.[5]Marine heatwaves, which have become more intense and longer-lasting under climate change, have doubled in frequency between 1982 and 2016.[6]

 


In addition of warming waters, Florida Keys is also threatened by rising sea levels (Image source: Florida Keys News Bureau)

 

The consequences of a warming ocean are wide-ranging. The ocean plays a vital role as the Earth's largest carbon sink, absorbing carbon dioxide from the atmosphere.[7]However, as the ocean heats up, it becomes less efficient at capturing carbon dioxide, exacerbating global warming further.

 


The ocean carbon cycle (Image source: IAEA)

 

Warming waters also contribute to the intensification of storms by providing more energy and moisture.[8]This leads to stronger and faster typhoons, posing risks to coastal communities and maritime activities.

Ecosystems like coral reefs and kelp forests, which are crucial for marine biodiversity and provide numerous benefits to humans, are under increasing thermal stress. Coral reefs, for example, undergo bleaching when exposed to prolonged periods of high water temperatures. Kelp forests are also declining at a rate of about 2% per year,[9]disrupting the delicate balance of marine ecosystems.

 


Marine heatwaves are causing Australia’s Great Barrier Reef to undergo bleaching (Image source: Getty Images)

 

The warming ocean also directly affects the fishing industry. As water temperatures exceed comfortable ranges, certain fish species move poleward in search of cooler waters.[10]This forces fishermen to travel further out to catch fish, leading to increased fuel consumption and carbon emissions. Additionally, both wild and farmed species such as crabs and oysters experience stunted growth or mass die-offs due to changing ocean conditions.[11][12]This results in significant economic losses and sometimes necessitates setting moratoriums to stabilise populations.

In response to these challenges, communities are taking measures to build climate resilience in the fishing industry. For instance, Japan's Fisheries Agency is promoting the use of electric fishing boats to reduce fuel costs.[13]In Australia, the Commonwealth Scientific and Industrial Research Organisation is collaborating with a salmon hatchery to develop heat-tolerant strains of salmon.[14]In Europe, proposals are being made to encourage the sales and consumption of alternative, more sustainable species to reduce vulnerability to climate change.[15]

 


Increasing diversity of the fishes we eat can improve the sustainability of the fishing industry (Image source: Darryl Jory)

 

It is crucial to recognise that climate change is not all just about hotter summers and more intense typhoons, it affects food security as well. Global warming has a profound impact on the ocean and the fishing industry, adversely affecting fish populations, coral reefs, and other important habitats. More than 3 billion people rely on fish and shellfish as important sources of nutrition,[16]and 600 million people depend on fisheries and aquaculture for their livelihoods.[17]Even in Hong Kong, seafood is a significant part of our diet, and the local fishing industry meets nearly one-fifth of the demand.[18]It is imperative that we address climate change and build climate resilience for the long-term sustainability of the ocean and the livelihoods of those who depend on it.




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