Seismic data confirms ocean waves from storms have become more widespread and ferocious due to climate change, according to a study from Colorado State University that the National Science Foundation funded.
Some, if not most, of my joy in life, was spent using my body as a surfboard at some of the world’s best beaches. But respect for the ocean is critical for the survival of anyone entering its water. Because waves can be very dangerous for swimmers, slamming you into the sandy bottom at the shore break or, even more dangerous, slicing your flesh off on a coral reef.
Waves cause shoreline erosion, can split large ships in two, destroy infrastructure, and necessitate the retreat from such communities in Bangladesh, Alaska, or Louisiana.
The wind is what forms waves. And warming ocean temperatures trigger more and higher waves. As the climate system unravels, this will be a significant part of our future, joining storm surges and rising seas as threats to the world's coastlines.
EOS, a publication of the American Geophysical Union, found that more severe impacts of wave height will impact the Southern Ocean. The most worrying thing in my mind is the impact of the battering of more powerful waves, the massive ice cap of Antarctica that has experienced significant sea ice decline where waves can more easily batter the ice shelves of glaciers and glacier tongues such as Thwaites and Pine Island.
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.
Meanwhile, Richard Aster of Colorado State University wrote in The Conversation, How global warming shakes the Earth: Seismic data show ocean waves gaining strength as the planet warms.
As oceans waves rise and fall, they apply forces to the sea floor below and generate seismic waves. These seismic waves are so powerful and widespread that they show up as a steady thrum on seismographs, the same instruments used to monitor and study earthquakes.
That wave signal has been getting more intense in recent decades, reflecting increasingly stormy seas and higher ocean swell.
In a new study in the journal Nature Communications, colleagues and I tracked that increase around the world over the past four decades. These global data, along with other ocean, satellite and regional seismic studies, show a decades long increase in wave energy that coincides with increasing storminess attributed to rising global temperatures.
What seismology has to do with ocean waves
Global seismographic networks are best known for monitoring and studying earthquakes and for allowing scientists to create images of the planet’s deep interior.
These highly sensitive instruments continuously record an enormous variety of natural and human-caused seismic phenomena, including volcanic eruptions, nuclear and other explosions, meteor strikes, landslides and glacier-quakes. They also capture persistent seismic signals from wind, water and human activity. For example, seismographic networks observed the global quieting in human-caused seismic noise as lockdown measures were instituted around the world during the coronavirus pandemic.
However, the most globally pervasive of seismic background signals is the incessant thrum created by storm-driven ocean waves referred to as the global microseism.
The most energetic of the two, known as the secondary microseism, throbs at a period between about eight and 14 seconds. As sets of waves travel across the oceans in various directions, they interfere with one another, creating pressure variation on the sea floor. However, interfering waves aren’t always present, so in this sense, it is an imperfect proxy for overall ocean wave activity.
A second way in which ocean waves generate global seismic signals is called the primary microseism process. These signals are caused by traveling ocean waves directly pushing and pulling on the seafloor. Since water motions within waves fall off rapidly with depth, this occurs in regions where water depths are less than about 1,000 feet (about 300 meters). The primary microseism signal is visible in seismic data as a steady hum with a period between 14 and 20 seconds.
What the shaking planet tells us
In our study, we estimated and analyzed historical primary microseism intensity back to the late 1980s at 52 seismograph sites around the world with long histories of continuous recording.
We found that 41 (79%) of these stations showed highly significant and progressive increases in energy over the decades.
The results indicate that globally averaged ocean wave energy since the late 20th century has increased at a median rate of 0.27% per year. However, since 2000, that globally averaged increase in the rate has risen by 0.35% per year.
We found the greatest overall microseism energy in the very stormy Southern Ocean regions near the Antarctica peninsula. But these results show that North Atlantic waves have intensified the fastest in recent decades compared to historical levels. That is consistent with recent research suggesting North Atlantic storm intensity and coastal hazards are increasing. Storm Ciarán, which hit Europe with powerful waves and hurricane-force winds in November 2023, was one record-breaking example.
The decadeslong microseism record also shows the seasonal swing of strong winter storms between the Northern and Southern hemispheres. It captures the wave-dampening effects of growing and shrinking Antarctic sea ice, as well as the multi-year highs and lows associated with El Niño and La Niña cycles and their long-range effects on ocean waves and storms.
Together, these and other recent seismic studies complement the results from climate and ocean research showing that storms, and waves, are intensifying as the climate warms.
Our results offer another warning for coastal communities, where increasing ocean wave heights can pound coastlines, damaging infrastructure and eroding the land. The impacts of increasing wave energy are further compounded by ongoing sea level rise fueled by climate change and by subsidence. And they emphasize the importance of mitigating climate change and building resilience into coastal infrastructure and environmental protection strategies.
Incredible footage of major coastal flooding and giant waves from Storm Bettina in Sochi, Russia along the Black Sea this morning. pic.twitter.com/Jua8ktpi9G
