The Hidden Impacts of Climate Change 4: Ocean Heatwaves

When you hear about climate change, what is the first thing you think about? Deforestation? Rising sea levels? Or global warming? Although the research behind these categories is already daunting, are we being told everything? 

In this series, the hidden impact of climate change, I will be digging deeper into the true effects that climate change has on our planet. Not only on humans, but also on the environment and animals. 

This is part 4 of the Hidden Impacts of Climate Change.

Aren’t heatwaves just a summer thing…?

There are many misconceptions on heatwaves, such as when it occurs, its causes and its meaning. So, firstly I am going to explain what heatwaves are about. By definition a heatwave is a period of excessively hot weather, which may be accompanied by high humidity. However, definitions vary relative to the usual weather in an area and normal temperatures. For example, what can be considered normal weather in the Sahara Desert can be termed as a heatwave in Scandinavia, a cooler area.

This means that people perceive heatwaves differently, depending on their region, so there is no general accepted definition that can be applied worldwide, as summers in the Northern and Southern hemisphere have different ranges in longevity. This means that definitions can only be shared by a few countries or by a country who has their own unique one. So, to know when it occurs can also be difficult to categorise. For the most part, they are most common in summer.

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Another common misconception of heatwaves is that climate change is a cause of heatwaves. The frequency of heatwaves increases due to climate change, but they have always existed before climate change. Therefore, it is a factor and it is not causation. In a high-pressure system, air from higher levels of our atmosphere gets pulled toward the ground, and as it descends it becomes compressed and increases in temperature. Also, humidity is a key factor which affects how hot it feels. An example of this is if it was 32 Degrees Celsius, and the relative humidity is 75%, it would result in weather feeling like 43 Degrees Celsius.

As humans, most of us enjoy the hot weather and heatwaves are welcome to some, however to much of a good thing is never good. The health effects are often overlooked, which leads to people undermining the danger heatwaves can hold. Hyperthermia, dehydration and heat exhaustion are just a few of many heat-related issues a heatwave can cause, and we are now seeing cases of these rise. But what if I told you that it is not only humans that endure the brutal consequences of heatwaves? Most of us have only perceived heatwaves as a land and human problem, but what about underwater? In this article I will summarise a topic that has been mostly overlooked, and is essentially a hidden problem that endangers sea animals; an extension from Animal Crisis.

How can there be a heatwave underwater?

Aside from the fact of melting ice caps and glaciers leading to rising sea levels, almost all of the current understanding of the ocean is restricted to what happens on the surface, where researchers can use satellite instruments to map the temperature and track events in near-real time. But beneath the surface is a world of complex currents. As a result, the animals underwater are often forgotten when we talk about the ocean and water in general, so what is going on there?

Ten years ago, dead fish began washing ashore on the beaches of Western Australia. The culprit was a huge swathe of unusually warm water that ravaged kelp forests and scores of commercially important marine creatures, from abalone to scallops to lobster. Over the following weeks, some of Western Australia’s most lucrative fisheries came close to being wiped out. To this day, some of them have not recovered. An example of a stark warning that has been imposed so forcefully. Researchers have found many heatwave events in oceans around the world, and they generally agree that they involve warm spells in surface waters of the ocean that last at least five days and reach a temperature threshold well above the normal range.  

The detrimental effects are being uncovered, but as research continues, researchers have already spotted worrying signs initiated by the ocean heatwaves; disruption in the food chain due to rapidly declining populations of animals and plant specie, also massive amounts of coral bleaching have occurred around the world in the last few decades. Coral bleaching is also a very serious problem where human awareness is low. It is a process where coral turns white due to stressors such as, temperature, light, or nutrients. These events and the subsequent loss of coral coverage often result in the decline of fish diversity. The loss of diversity and abundance in herbivorous fish particularly affect coral reef ecosystems. As mass bleaching events occur more frequently, fish populations will continue to homogenise. Smaller and more specialised fish species that fill particular ecological niches that are crucial for coral health are replaced by more generalised species. The loss of specialisation likely contributes to loss of resilience in coral reef ecosystems after bleaching events.

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The disruption in the food chain was typified when warm, low-nutrient water in the Northwest Pacific during a 2013–16 marine heatwave known as ‘The Blob’ devastated phytoplankton growth. Then, Chinook salmon populations plunged, and as many as one million seabirds died in the Gulf of Alaska. The Blob also increased surface water temperatures on the western coast of North America up to 5 Degrees Celsius in some areas. Climate change only exacerbates this issue by increasing these temperatures and extending their length. This not only affects animals and plants underwater though. These factors increase the urgency exponentially; food security, the seafood market, and more extreme weather. The obvious impact is how drastic falls in fish population would impact us as humans. But the more you think about it, the more serious it seems. For example, if large swathes of fish disappear, the populations dependent on these fish would struggle to adapt to the sudden change, as these communities are often poor ones where the local economy has no protection. In the seafood market, the ocean provides us with billions of pounds’ worth of food and resources, threatened by these heatwaves. This means that, developed countries may be worse of as a whole financially, as this industry is an integral part of every economy. In addition, both of these repercussions are being made worse as plants underwater are being damaged; a vital part of the ecosystem and a natural resource that keeps the climate in balance.

Monitoring ocean heatwaves and their results

After the disaster in Australia, the Integrated Marine Observing System (IMOS) and its partners have maintained a fleet of ocean gliders – underwater, remotely pilotable instruments that are on standby. When a marine heatwave develops, the IMOS team can mobilize quickly to get its gliders in the water to collect key data about temperature and salinity. Earlier this year, the researchers used a glider to track the development of what turned out to be the strongest marine heatwave in that part of the ocean since the event 10 years ago. The glider swam more than 500 kilometres and captured the cooling effect of a tropical cyclone that tore through the waters in early February. In March and April, the team deployed two more gliders off the coast of Tasmania (an Australian state)  to help map the extent of a persistent heatwave in the Tasman Sea. The researchers say that data collected by these gliders could help to improve predictions from dynamical forecasting models, which simulate the physics of processes in the ocean and atmosphere.

Forecasting efforts around the world are currently unable to predict the extremes very far in advance, says Alex Sen Gupta, a climate scientist and oceanographer at the University of New South Wales in Sydney. “The science of ocean forecasting is quite a long way behind the science of weather forecasting.” This echoes how technology has not been utilised in this unique manner, emphasising how little the public attention is on this issue. Nonetheless if ways are developed to notice patterns and make short-term projections now, this problem would be able to be better translated amongst society. Therefore, government funding is imperative if we are to combat the growing intensity of ocean heatwaves; to fund research capacity, as well as the private sector where investment would be needed to protect the fishing industry.

Research should aim to establish a temperature baseline which considers species’ thermal limits, and combine physical and biological data to better predict future conditions and highlight biodiversity most at risk. This would allow preventative measure to be put in place to stop mass extinction for vulnerable species. It is almost impossible to tackle this problem directly, as we cannot stop warm water mixing with cold water elsewhere, due to it being unfeasible to prevent currents moving. But this is an area that is being researched as we speak, and not only that, it is probably the hardest problem to correct. Why? In this case, we are looking out for the biodiversity underwater, therefore meaning humans are not directly put in danger this situation, which leads to serious commitments having to be made. So, we need to take into consideration how these waters are heating up, the movements of the currents and the biodiversity. If we directly cool the ocean somehow, we would not even know the effects of doing that, as we still have a lot to learn under the surface of the ocean.

What do we do then? Well, the only way to take direct action at this moment in time is to prevent global warming getting worse. Unfortunately, this means we have no control and have little knowledge on how underwater heatwaves will behave and interact, apart from the fact that we know that they are becoming more frequent.

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Throughout this article, I have talked about what is being done as well as why and how, and the effects it can have theoretically in the future. This section will introduce the concrete progress we have made in our understanding of ocean heatwaves so far.

Heat Bombs (a factor affecting ocean heatwaves):

 Research primarily funded by the Office of Naval Research describes so-called underwater “heat bombs” as one of many mechanisms by which global warming-driven encroachment is changing the nature of the Arctic Ocean faster than nearly any other place on Earth. It adds to a growing body of evidence that suggests that Arctic Sea ice, a source of global climate stability, could disappear for larger portions of the year. Ice in the Artic Ocean have layers which are controlled by salinity rather than temperature. This forms a fresh, icy layer on the surface of ocean waters which is then mixed with warm, salty and dense water, through the Bering Strait. The warm water goes under the fresh icy layer, drawing nutrients, stimulating phytoplankton growth; the process where the warm water subducts has not been directly observed nor understood, but it is known that the travelling water is saltier and is denser in this situation. Then pockets of warm water stay below the surface for months or years and circulate in spinning eddies as they interact with the surrounding water – heat bombs. Researchers have hypothesised that this accelerates the surface ice melting and their heat diffuses upwards on their journey towards the artic. The Office of Naval Research Stratified Ocean Dynamics of the Artic (SODA) program, was designed to understand the details of the changing Artic using novel instruments, satellite observations and profiling float data. This has enabled them to decode the most complicated physics.

On the other hand, there have been many research projects that are still ongoing regarding ‘The Blob’. All of the groups are making sense of an unfamiliar event, in ways such as analysing currents, using its damage and quantifying it to make predictions, as well as how other less known ocean heatwaves compare. It is vital that this event is fully understood because it will allow patterns and trends to be noticed, and aid analyses for future ocean heatwaves. It wouldn’t provide a basis as it cannot be treated as having reliable, consistent facts, due to it only being one large event, however with other data on ice and other factors determining the intensity of these heatwaves, this knowledge would be invaluable in the search for potential solutions.

Closing words

Marine heatwaves clearly have the potential to devastate marine ecosystems and cause economic losses in fisheries, aquaculture, and ecotourism industries. However, their effects are often hidden from view, under the waves, until it is too late. By raising general awareness of these phenomena, and by improving our scientific understanding of their physical properties and ecological impacts, we can better predict future conditions and protect vulnerable marine habitats and resources.

Individuals may feel powerless at their inability to positively improve this dilemma. However, donations and funding can make a large impact on this mysterious predicament, as to ensure the necessary resources are available. But as researchers and scientists furiously work on their understanding of this matter, hopefully we can collectively stop the worst-case scenario for life underwater.

If you want to read about heatwaves in general or ocean heatwaves, the following links include more information:

Thank you for reading!

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