The oceans surrounding the UK and Ireland are currently experiencing one of the world's worst marine heatwaves (MHWs), with some locations experiencing temperatures up to 4°C above the seasonal average. The average surface temperature of the North Atlantic Ocean peaked on June 17 at 23 degrees Celsius, 0.2 degrees above the previous record high set in 2010. The last three months have seen record-breaking temperatures in the region. Scientists at the US National Oceanic and Atmospheric Administration have classified the area as being affected by a category 4 (severe) maritime heatwave because much of the heat is presently centred on the waters bordering the UK and Ireland.[i]
The Atlantic Marine Heatwave, as recorded by the European Space Agency
Over the past ten years, MHWs have grown by 50%, lasting longer and being more severe. Weeks or even years may pass between MHWs. They may only impact a tiny portion of a shoreline or cover many oceans. In surface and deep waters, at all latitudes, and in a variety of marine environments, MHWs have been seen. According to projections, MHWs will occur up to 50 times more frequently than before the industrial revolution, increase in frequency by 20–50 times, and intensify by 10 times by 2100. As MHWs increase in frequency and severity, they risk pushing ecosystems over the point of no return, which would have long-term effects on marine biodiversity and the many millions of people whose livelihoods depend on it.[ii] Increased ocean temperatures brought on by MHWs can lead to hurricanes and tropical storms, alter the water cycle, and increase the likelihood of floods, droughts, and land-based wildfires. For coastal areas, MHWs have additional significant socioeconomic effects. While fisheries rely on species that frequently migrate in response to changing climatic conditions, aquaculture, for example, needs water temperatures to remain suitable for farmed species. Economically significant species, such as lobster and snow crab in the northwest Atlantic and scallops off Western Australia, have been demonstrated to be killed or have their productivity reduced by MHWs. Such impacts also have knock-on impacts on local and regional tourism.[iii]
They examined 34 marine heatwaves worldwide and discovered that one in southern Chile in 2016 caused direct losses to aquaculture, the practise of raising aquatic plants and animals for food, of more than US$800 million. Another heatwave that affected the seagrass beds in Shark Bay, Western Australia, caused indirect costs of US$3.1 billion annually due to the loss of carbon storage. The "ecosystem services" of the ocean, or the variety of advantages that healthy marine ecosystems offer humans, are altered by heatwaves, which result in significant economic losses.[iv]
Indirectly, the impacts of MHWs can also lead to increased soil erosion and, therefore, a loss of beaches. The loss of kelp and seagrass habitats as well as more intense tidal flows, means sand and silts are more likely to be washed away.[v] In Tunisia, this has led to the 85% of the population living on the coast to suffer economic woes. A little more than 80% of enterprises, including restaurants and coffee shops, have been harmed along the parts of Ghannouch's (a town on the coast of Tunisia) shoreline that have been most severely affected. Sassi Alaya, the head of the fisheries guild in the town's southern port, says that half of the local fishermen have been affected along the most eroded areas of the coastline. "The rising sea levels and the disappearing sand have severely harmed businesses on the beach," claims Alaya, noting a significant reduction in tourists over the past ten years. Additionally, Gil Mahé, research director for the hydrosciences laboratory at France's Montpellier University, claims that it is a "major blow to agriculture". As coastal erosion in Tunisia worsens, saltwater seeps inland and destroys fertile land. Mahé goes on to say, "What about all the coastal infrastructure that has been constructed? Ports? nuclear energy sources?“[vi]
The impact of MHWs can be frightening, but there is hope for the future management of their effects. For example, a marine heatwave in the US Gulf of Maine in 2012 cost the lobster industry US$38 million. This resulted from a sudden increase in the supply of lobsters, which led to a glut, and a sharp decline in the price lobster fisherman were paid for their catches. However, the same lobster fishery made an additional US$103 million in 2016 as a result of a second marine heatwave thanks to experience learned since the first, which allowed them to benefit from the increased lobster capture rates.[vii] This highlights an important lesson for any whose livelihood relies upon the oceans, that adaptation is possible, but preparation and prediction are key in not having to learn the hard way.
Research into how such predictions could work, which was published in Nature, lays the groundwork for a functioning system for forecasting marine heatwaves that can do so up to a year in advance. The projections have the best "skill" in the tropics, but the authors discover that they are less accurate across much of the Southern Ocean, which frequently suffers powerful but transient marine heatwaves. The authors also note that the intense 1997–1998 and 2015–2016 El Niño occurrences had the "highest prediction skill" over the 30-year dataset. Systems that accurately predict marine heatwaves can be useful tools for boosting the adaptability of marine ecosystems. For instance, early notice of heatwaves could help fisheries prevent overfishing of some species when high water temperatures lower productivity.[viii]
Marine scientists have suggested that one adaptive strategy could be to reduce industrial pollution in order to create conditions where sea grass and other species can better handle the stresses of MHWs. Where this is not possible, more significant policy adjustments may be required to help coastal towns expand their range of economic options to include both fishery-related and non-fishery enterprises. The focus should be placed on flexible management strategies that permit quick adaptation to the effects of environmental variation, such as heatwaves, in addition to expanding the scope of Marine Protected Areas. However, best practices should also include funding for coastal communities to help them adapt to climate change's effects, ensuring that communities are safeguarded from the physical repercussions and helped in their endeavour to achieve economic security.[ix]
[i] New Scientist- UK and Ireland suffer one of the most severe marine heatwaves on Earth
[iii] Ibid
[v] Ecosystem Collapse and Climate Change- Impact of Marine Heatwaves on Seagrass Ecosystems
[vi] Reuters- Why are Tunisia’s beaches disappearing and what does it mean for the country?
[vii] Ibid
[viii] Nature- Global seasonal forecasts of marine heatwaves
Oscar is a recent graduate with a background in earth science. He is currently studying an MSc focussing on disaster responses, emergency planning and community resilience. His postgraduate research project will assess the link between climate crisis risk perception and attitudes to green energy projects. “Adapting to the climate crisis through the pursuit of net zero requires community engagement and understanding. Zero Carbon Academy’s goals closely align with this approach and I’m excited to have the opportunity to research and communicate a variety of topics relating to our environment and sustainability”.
