Faster winds and bigger waves have wide implications

The finding that oceanic wind speeds and wave heights have increased significantly over the last quarter of a century is likely to have major implications for maritime industries and climate scientists alike.

Last week Science published the results of a wind and wave study undertaken here at Swinburne University. Based on 23-years of satellite data, it revealed trends for increased wave heights and surface-wind speeds.

While the patterns were not uniform geographically, it was clear that overall, both mean and extreme values grew significantly during the period observed.

These trends are quite startling and will have a significant impact on costal and offshore engineering, navigation and even town planning. For example, beach erosion is linked to extreme storms and, as the study has shown, extreme storms are becoming more frequent and severe.

The finding also has major implications for air-sea interaction studies and climate research. Increased wind speed and wave heights could have a profound effect on the transfer of energy (heat) between the sea and the atmosphere, which is one of the great unknowns of climate change.

This means that – alongside routine measurements of temperature and rainfall – oceanic wind speeds and wave heights can serve as indicators, or even proxies, for what is happening to the climate.

In the air-sea system, all environmental properties are interconnected and dependent on one other.

Temperature differences create pressure patterns, pressure gradients drive winds, which generate waves, waves negotiate air-sea exchanges and facilitate ocean mixing and finally the ocean’s mixed layer affects the atmospheric temperature and its distribution.

Therefore, wind and waves can act as rich environmental indicators of variations to climate.

This is good news for climate scientists, as trends in this area can be reliably detected. And unlike temperature, winds and waves possess kinematic characteristics – velocity and direction, which can potentially provide additional information about climate variation. For instance, changes to pressure may result in changes to wind speed, as well as changes to wind and wave direction.

Another factor that makes wind and wave data so valuable is the coupled nature of the atmosphere-ocean system. Changes to wind and waves not only indicate changes in the air-sea body, they also negotiate and influence them.

While the observed findings clearly show that wind and wave growth has occurred, at this stage we do not have a clear understanding of what has caused it.

Some may be keen to attribute it to human-induced climate change. However it’s possible that it may simply be a part of a long-term environmental oscillation. This means that extrapolation of such trends into the future has to be done with a great degree of caution.

In the absence of historic data about wind and wave climates, the sensible way to proceed in analysing the observed trends is through numerical simulations. By coupling existing climate models with wave models, scientists will be able to gain a better understanding of what the globe’s wind and wave growth really means.

by Alex Babanin and Stefan Zieger of Swinburne University.

Read more at Science Magazine