Waves crash over Newhaven Lighthouse in Newhaven, England, on Thursday. Winds up to 108 mph slammed France’s Atlantic coast overnight as Storm Ciarán lashed countries around western Europe, uprooting trees, blowing out windows and leaving 1.2 million French households without electricity. Kin Cheung/Associated Press
When an ocean wave falls, the ground shakes. Now, those wobbles are getting bigger.
Stormier seas and larger ocean swell in recent decades are pounding Earth’s seafloor with more force, sending larger ripples through Earth’s crust – almost like a tiny, tiny, tiny earthquake. The biggest wave energy increases, as measured with a seismometer, appear in the North Atlantic Ocean, according to recent research.
The heightened force tracks with rising global temperatures, which can supercharge storms and make them bigger and more intense. These storms, compounded with rising sea levels, further erode land and threaten communities living on the coast.
“As the waves get bigger, they push and pull harder on the floor of the ocean,” said Rick Aster, seismologist and lead author of the study.
Wave energy across the world has increased 0.27% per year, on average, since the 1980s, the research found. It has been worse in recent years, increasing by 0.35% each year since 2000. A few tenths of a% per year adds up over the decades, Aster said, amounting to about an 8% increase over 30 years.
Oceans are the background buzz of Earth. Falling waves are constantly hitting the seafloor, sending small pulses to even the deep interiors of continents. Take out human activity, glacier quakes, earthquakes, landslides, volcanic eruptions, meteor strikes, nuclear and other explosions, and you’re left with ocean vibes.
Seismometers, which measure the movement of the ground typically from earthquakes, can pick up the seismic waves from the thrashing ocean. Analyzing data from more than 50 stations worldwide, the team observed these high-seas vibrations traveling across long distances as a steady hum. Imagine waves crashing onto Earth’s crust like a finger plucking a guitar string, but creating waves on a much larger scale.
The length of a wave is “tens of kilometers, and they actually propagate in the crust of the earth, so they’re really big beasts,” said Aster, head of the Geosciences Department at Colorado State University. “In the absence of earthquakes or other large transient events, it’s the dominant seismic signal on our planet.”
You wouldn’t feel the ground shaking because the motion is on the scale of microns. You also wouldn’t be able to listen to any rumbles because they occur on scales way below our hearing. But we recognize these large sets of waves – the kind that excite surfers from California or Hawaii. They’re created from big storms that have high winds over long distances, Aster said.
And these gnarly waves are more common than you may think, constantly hitting Earth’s seafloor because “somewhere in the world, there’s a giant storm generating these waves,” he said.
The most surprising aspect of the study, Aster said, was that the wave energy increase was “happening almost everywhere on the planet.” Around 80% of stations showed highly significant and progressive increases in energy over the decades – a fact that would “never occur by chance.”
“Global warming puts increased energy in the atmosphere, resulting in stronger storms with intensified winds that generate increased wave heights,” said oceanographer Peter Bromirski, who was not involved in the study. For example, more water is evaporated into a warmer atmosphere and becomes fuel for storms.
The most powerful waves were found in the Southern Ocean around Antarctica, not surprising for the sea known as the stormiest in the world. Aster explained the region is the only place where the ocean water can circle around the planet with no interruptions from landforms.
But the North Atlantic Ocean experienced the highest increase in wave energy over the past four decades, compared to historical levels. Wave energy increased, on average, more than twice the global rate since the 1980s, with seismic stations in the eastern United States showing increases between 0.6 and 0.8% per year.
The increase in the North Atlantic is stark but falls in line with other recent record activity in the region. The area, including the Gulf of Maine, is home to some of the fastest-warming water in the world. It also has experienced more rapidly intensifying or record storms, such as deadly Storm Ciarán, which pummeled the United Kingdom at the beginning of November. Hurricanes are also transitioning into big storms in the region, such as from Hurricane Ida.
Wave energy also increased across the world during periods of El Niño and La Niña, when sea surface temperatures change in the eastern Pacific Ocean. Storm activity increases in the Atlantic basin during La Niña and heightens in the central and eastern Pacific Ocean during El Niño – increasing on a global average during either event.
“It’s really a measure of what the big storms are doing around the world,” Aster said.
Hotter ocean waters caused by global warming, Aster noted, are also heightening effects felt from later El Niño and La Niña, sometimes producing more extreme ocean waves than a similar event decades earlier on a comparatively cooler Earth. Today’s El Niño, Aster said, may not be the same as “your father’s El Niño.”
Wave activity should continue to intensify as long as temperatures keep rising, said Bromirski, oceanographer emeritus at Scripps Institution of Oceanography. This increase, which he previously documented in waves along the California coast, has been evident since global warming surged in the 1970s. Some say global temperatures are accelerating even faster now.
“Global surface temperatures during the last decade indicate that global warming is again accelerating,” Bromirski said. “Further increases in wave activity along coasts potentially will follow, aggravating issues from higher tides associated with sea level rise.”
More intense waves can make it harder for people to safely live on coasts, said Itxaso Odériz, a coastal hazard researcher who was not involved in the study. Ocean waves help shape beaches, estuaries, ecosystems, ports and tourism spots. Breaking waves transport sediment, change the position of the shoreline and run up steep slopes.
“If the waves are extreme, generated by storms such as extratropical cyclones, sediment transport can be substantial, causing erosion and affecting coastal infrastructure,” said Odériz, researcher at IHCantabria Instituto de Hidráulica Ambiental de la Universidad de Cantabria. “The water level can rise significantly, leading to coastal flooding.”
Observations showing when, where and how waves are increasing across the planet, she said, are vital to quantifying coastal risk – especially in conjunction with data on how seas are rising along coastlines.
“It’s another wake-up call for people to really get serious about paying attention to coastal infrastructure and ecosystem in a world that’s going to have larger waves on average,” Aster said.
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