During extreme storms, the ocean waves can be high over 20 meters or high as a five storey building.
More than just a product of our meteorological systems, waves are critical to sea shipping, beach stability, coastal floods or floods, and the design of coastal and offshore structures.
But our new study, published in Science, shows that these waves and the winds that generate them are increasing in size and doing so over the last 30 years.
These new measurements show that global average wave conditions are increasing, but more importantly, extreme wave conditions are rising even faster, with the largest increases occurring in the South Ocean.
We have found that the extreme winds in the South Ocean have increased by about 1.5 meters per second or by 8% over the last 30 years. Similarly, extreme waves in the same region increased by 30 centimeters or 5 per cent. Generally, winds grow faster than waves.
In addition to the increases in the South Ocean, extreme winds have also increased in the equatorial parts of the Pacific Ocean and the Atlantic Ocean, and the North Atlantic Ocean is approximately 0.6 meters per second over a period of 30 years.
These changes in the ocean wind and wave climate were determined by creating and analyzing a database of satellite wind speed and wave velocity measurements.
We used data from a total of 31 satellites in orbit between 1985 and 2018. For more than thirty years, these satellites made approximately 4 billion measurements of wind speed and wave height.
Although the dataset is huge, all satellites need to be very precisely calibrated. This was done by comparing satellite measurements with more than 80 ocean buoys all over the world. This is the largest and most detailed database of its type ever made.
It is important that within the combined data base there are three different forms of satellites – altimeters, radiometers and scalers. They use different methods to measure ocean waves, so combining them provides an even more stable set of data.
Expansion to extreme wave height is less uniform than winds. In addition to the increases in the South Ocean, the extremes of the extreme waves are also increasing in the North Atlantic. The speed of wind speed and wave height increase is shown in the above graphs.
Although increases of 5% for waves and 8% for winds may not look great, if they are maintained in the future, such changes in our climate will have major consequences. The potential impacts of climate change-induced sea levels are well known. What most people do not understand is that actual floods are caused by storms and waves associated with storms.
Elevated sea level just makes these wind and wave events more serious and more frequent. Increasing the height of the waves and other properties, such as the wave direction, will further increase the probability of flooding the coast. Such changes will lead to increased coastal erosion, putting coastal settlements and infrastructure at risk.
We still do not know if historical increases will be retained in the future. One of the important applications of the extensive satellite database will be the calibration and validation of the next generation of global climate models that now include ocean waves forecasts. The early results of such models give similar results to historical data, and in particular point to changes in the South Ocean.
Changes in the South Ocean are important as it is the origin of the bay, which dominates the waves of the South Pacific, the South Atlantic and the Indian Ocean, and determines the stability of the beaches for much of the southern hemisphere.
Changes in the South Ocean can have an impact around the world, with violent waves that increase coastal erosion, and jeopardize fishing villages and infrastructure.
International research teams, including the University of Melbourne, are now working to develop the next generation of global climate models to design changes in winds and waves over the next 100 years.
We need a better understanding of how much of this change is due to long-term climate change and how much it is due to plural fluctuations or cycles.
This article was first published on Pursuit. Read the original article.