Effects of Global warming

 Global warming is shaking the Earth

Oceans waves apply forces to the sea floor below and generate seismic waves as they rise and fall. These wave signals have been getting more intense in recent decades, reflecting increasingly stormy seas and higher ocean swell. These seismic waves are so powerful and widespread that they show up as a steady thrum on seismographs which is used to monitor and study earthquakes. In a new study consisting over the past four decades around the world, data was collected. This global data, along with other ocean, satellite and regional seismic studies, show a decades long increase in wave energy which coincides with increasing storminess attributed to rising global temperatures around the world.

Science of seismology 

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 capture persistent seismic signals from wind, water and human activity. They also 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. For example, seismographic networks observed the global quieting in human-caused seismic noise as lockdown measures were instituted during the coronavirus pandemic around the world.

Types of seismic signals

Ocean waves generate micro seismic signals in two different ways. The most energetic of the two, known as the secondary micro seism, 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 situation, 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 micro seism 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 micro seism signal is visible in seismic data as a steady hum with a period between 14 and 20 seconds. However, the most globally pervasive of seismic background signals is the incessant thrum created by storm-driven ocean waves referred to as the global micro seism.

In the study, we estimated and analysed historical primary micro seism intensity back to the late 1980s at 52 seismograph sites with long histories of continuous recording around the world . 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 micro seism 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. This 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.

Ocean wave intensification is being observed since the late 1980s: Each circle is a seismic station, with size proportional to the vertical acceleration of the Earth at that station smoothed over three years. Red circles indicate periods when ground motions are larger than the historical median; blue indicate periods when they are smaller. The synchronized graph shows the median vertical acceleration anomaly for all stations and reflects El Niño cycles and a more pronounced increase in recent years. 

In November 2022, Hurricane Nicole’s intense waves eroded the land beneath several homes in Daytona Beach, Fla. 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. The decades long micro seism 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.

The oceans have absorbed about 90% of the excess heat connected to rising greenhouse gas emissions from human activities in recent decades. This excess energy can translate into more damaging waves and more powerful storms. 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 on going sea level rise supported 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 around the world.