Larger Waves In Store As The Planet Warms

Eos - Katherine Kornei

By the end of the 21st century, waves will have gotten larger in some ocean basins, particularly the Southern Ocean, climate modeling reveals.

The Southern Ocean, which skirts Antarctica, may experience larger waves as the climate warms. Credit: Mike Hill/Stone/Getty Images

Life-sustaining. Beautiful. Destructive.

Ocean waves are all of those—they transport nutrients that nourish marine life, but they also damage ships and batter coastlines, triggering erosion that can send homes and roads tumbling.

Now, scientists have used climate models to show that some parts of the globe, including the Southern Ocean, are likely to experience larger waves by the end of the 21st century.

That’s potentially bad news for coastal residents, the researchers suggest, because large waves could generate increased flooding and erosion.

Generated by Wind

Ocean waves are kicked up by the wind, and warmer conditions promote stronger winds. Larger waves might therefore be a hallmark of our planet’s future, Alberto Meucci, an oceanographer at the University of Melbourne in Australia, and his colleagues hypothesized. They set out to test that idea using climate models.

“If you want to be able to predict changes in extremes, having enough data to do so is important.”

The researchers focused on a metric known as significant wave height. Defined as the average of the highest one third of waves, it’s a commonly used parameter in oceanography. (Waves more than twice the significant wave height are called rogue waves. These watery monsters, which can top 25 meters, were dismissed as sailors’ tall tales for years before they were finally recorded using modern instruments.)

Many Climate Models

Meucci and his collaborators relied on two very different greenhouse gas emission scenarios.

One, Representative Concentration Pathway (RCP) 8.5 (the “business-as-usual” scenario), which assumes that carbon emissions will remain largely uncurbed, yields 8.5 watts per square meter of additional warming by the end of the 21st century (about 4.3°C). The other, RCP 4.5, assumes that some emissions mitigation policies are enacted and yields about 2.4°C of warming by 2100.

The researchers input both scenarios into seven different climate models. Meucci and his colleagues used multiple climate models to beat down statistical uncertainties. “The point of using seven global climate models instead of a single model was to be able to reduce the uncertainties connected with the representation of extremes,” said Meucci.

The novelty of this study is its use of multiple climate models, said Laure Zanna, a physical oceanographer at New York University not involved in the study. “If you want to be able to predict changes in extremes, having enough data to do so is important.”

Meucci and his collaborators fed the surface wind outputs of the climate models into wave generation models.

The scientists determined the 1-in-100-year significant wave height—corresponding to a wave that has a 1% probability of occurring each year—for both the RCP 8.5 and RCP 4.5 scenarios for two time periods: 1979–2005 and 2081–2100.

“Changes may be felt up to the North Pacific.”

The scientists found an increase in the 1-in-100-year significant wave height at the end of the 21st century in the Southern Ocean for both greenhouse gas emission scenarios. 

The largest difference, roughly 15%, was observed in the Southern Ocean for the RCP 8.5 scenario.

Larger waves might spell bad news for this region, which is already routinely battered by waves topping 20 meters, the team concluded.

Large swells could very well roll up on the coasts of South Africa, South America, and Australia, said Meucci, where they might contribute to flooding and coastal erosion. Their impact could also be more far-reaching, he said. “Changes may be felt up to the North Pacific.”

But not all ocean basins will experience larger waves, the team found. In portions of the North Atlantic, wave height might even decrease by the end of the 21st century, Meucci and his collaborators noted.

The researchers next investigated changes in the frequency of extreme waves. Again, the Southern Ocean stood out. That basin was more likely to experience large waves at the end of the 21st century compared with 1979–2005, the team found.

These findings are believable, but it’s important to pinpoint what’s driving the changes in the Southern Ocean, said New York University’s Zanna. “An understanding of the physical mechanisms would help strengthen even further their results.”

Links

• NASA Climate Change Warning: Rising Sea Levels Accelerating
• (AU) Land Projected To Be Below Annual Flood Level In 2050
• Doomsday: By 2300, Global Sea Levels Could Rise by An Astounding 16 Feet
• (AU) Erosion From Surging Seas Threatens Roads, Homes And Beaches
• Satellites Show Melting Ice Sheets In Antarctica And Greenland Have Contributed To 14 mm Sea Level Rise In 16 Years
• Why This Year Is Our Last, Best Chance For Saving the Oceans
• (AU) Climate Change In Deep Oceans Could Be Seven Times Faster By Middle Of Century, Report Says
• Damage From Climate Change Will Be Widespread And Sometimes Surprising
• Rising Tides, Troubled Waters: The Future Of Our Ocean
• India's Women Seaweed Divers Swim Against The Tide Of Climate Change
• A Revised View of Australia’s Future Climate
• Moving Beyond Impasse in Climate Change Communications