Local weather Change Makes Ocean Waves Stronger And Threatens To Erode Many Shorelines – Watts Up With That?
Thomas Mortlock, Macquarie University; Itxaso Odériz, National Autonomous University of Mexico (UNAM); Nobuhito Mori, Kyoto University, and Rodolfo Silva, National Autonomous University of Mexico (UNAM)
Sea level rise isn’t the only way climate change will devastate the coast. Our research published today found that it also makes waves stronger, particularly in the southern hemisphere.
We recorded the trajectory of these stronger waves and found that the coasts of South Australia and Western Australia, the Pacific and Caribbean islands, eastern Indonesia and Japan, and South Africa are already experiencing stronger waves due to global warming.
This will intensify the effects of sea level rise, expose low-lying island states in the Pacific – such as Tuvalu, Kiribati, and the Marshall Islands – to further threats, and transform our global coastal management.
But it is not too late to stop the worst effects – that is, if we drastically and urgently reduce greenhouse gas emissions.
An energetic ocean
Since the 1970s, the ocean has absorbed more than 90% of the heat extracted from the planet. This has a number of effects, including longer and more frequent ocean heat waves, coral bleaching, and providing a source of energy for stronger storms.
Since the 1980s at the latest, wave power has increased worldwide as more and more heat is pumped into the ocean
However, our focus has been on how ocean warming increases wave power. We looked at wave conditions over the past 35 years and found that global wave force has increased since at least the 1980s, mainly in the southern hemisphere as more energy in the form of heat is pumped into the oceans.
And a more energetic ocean in some parts of the world means greater wave heights and an erosive energy potential for the coasts than before.
Read more: Ocean warming threatens coral reefs and could soon make them harder to restore
Ocean waves have shaped the earth’s coasts for millions of years. Therefore, small, sustained wave changes can have long-term consequences for coastal ecosystems and the people who depend on them.
Mangroves and salt marshes, for example, are particularly vulnerable to the surge in wave energy combined with rising sea levels.
To escape, mangroves and swamps naturally migrate to higher elevations. But when these ecosystems return to urban areas, they have nowhere to go and become extinct. This process is known as “coastal squeezing”.
These ecosystems often provide a natural buffer against wave attacks for low-lying coastal areas. Without these peripheral ecosystems, the coastal communities behind them will be exposed to more wave energy and possibly more erosion.
Mangrove forests are among the most endangered ecosystems as sea levels rise and ocean waves crash more strongly against the coast.
Why is this happening?
Ocean waves are created by winds that blow along the ocean surface. And when the ocean absorbs heat, the ocean surface warms up, causing the warm air to rise above it (this is called convection). This helps to boost atmospheric circulation and winds.
In other words, we come to a cascade of effects: higher sea surface temperatures lead to stronger winds that change the global wave conditions of the oceans.
Read more: Inquisitive Children: Why Are There Waves?
Our research shows that in some parts of the world’s oceans, wave force increases due to stronger wind energy and the shift of westerly winds towards the poles. This is most noticeable in the tropical regions of the Atlantic and Pacific Oceans, as well as in the subtropical regions of the Indian Ocean.
But not all changes in wave conditions are driven by ocean warming from human-made climate change. Some areas of the world’s oceans are even more affected by natural climatic fluctuations – such as El Niño and La Niña – than by long-term ocean warming.
In general, changes in wave conditions towards the equator appear to be more driven by ocean warming due to man-made climate change, while changes in waves towards the poles are more influenced by natural climate variability.
Ocean waves are created by winds that blow over the ocean surface.
How that could erode the coasts
While the coastal response to climate change is a complex interplay of many processes, waves along many of the world’s open, sandy coastlines remain the main driver of change.
So how could coastlines react to being hit by stronger waves? It generally depends on how much sand there is and how exactly the wave force increases.
For example, if the wave height increases, it can lead to increased erosion. However, when the waves get longer (an extension of the wave period) it can have the opposite effect, moving sand from deeper waters to help the coast keep pace with rising sea levels.
Bondi Beach, Sydney. cool winter evening.
For low-lying nations in areas with rising sea surface temperatures around the equator, higher waves – combined with rising sea levels – represent an existential problem.
People in these countries can experience both sea level rise and increasing wave force on their coasts, eroding land further up the beach and damaging property. These areas should be viewed as coastal climate hotspots where continued adaptation or funding is required.
It is not too late
We are not surprised to find the fingerprints of greenhouse warming in the ocean waves and, consequently, along our coasts. Our study only examined historical wave conditions and how they are already being influenced by climate change.
However, if warming continues in line with current trends in the next century, we can expect more marked changes in wave conditions on the world’s coasts than our backward-looking research has revealed.
However, if we can mitigate greenhouse warming in line with the 2℃ Paris Agreement, studies suggest that we could still keep changes in wave patterns within natural climate variability.
Read more: Seabirds are today’s canaries in the coal mine – and they send us an urgent message
However, one thing is abundantly clear: the effects of climate change on waves are not a dream of the future and are already occurring in large parts of the oceans.
The extent to which these changes continue, and the risk it poses to global coastlines, will be closely linked to decarbonization efforts in the coming decades.
This story is part of Oceans 21
Our series on the global ocean began with five depth profiles. Keep an eye out for new articles on the state of our oceans in the run-up to the next UN climate change conference COP26. The series is brought to you by The Conversation’s international network.
Thomas Mortlock, Senior Risk Scientist, Risk Frontiers, Adjunct Fellow, Macquarie University; Itxaso Odériz, Research Associate, National Autonomous University of Mexico (UNAM); Nobuhito Mori, Professor, Kyoto University, and Rodolfo Silva, Professor, National Autonomous University of Mexico (UNAM)
This article was republished by The Conversation under a Creative Commons license. Read the original article.
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