Australasian Science: Australia's authority on science since 1938

Wind and Waves Rising

By Stephen Luntz

Wind speeds have increased over the past 23 years and wave heights have risen as a result.

A study published in Science has revealed that wind speeds have increased over the past 23 years and wave heights have risen as a result. Increases were larger at higher latitudes.

The findings are based on satellite data, and appear to contradict a previous study that reported decreases in wind speeds in continental USA over the period 1973–2005.

Swinburne University oceanographer Prof Alex Babanin says that the latest research is more reliable as it uses satellite data. While noting that some regions showed falling wind speeds, even as the global average was rising, Babanin argues that previous research “used data from airfields”. He says this largely misses changes that might happen in hilly areas.

“The periods of measurement were not necessarily continuous – the measurements were taken at specific times in the day,” Babanin adds. “Satellites are more or less uniform and don’t depend on the time of day.”

Wave measurements from ships are also compromised, Babanin says, as captains attempt to evade large storms and may have become better at this as technology has improved.

While satellites might not seem an obvious tool for measuring winds, Babanin says that some of the reflections they detect from the Earth are affected by wind speed.

The reason for rising wind speeds is not known. “It’s not necessarily climate change,” Babanin says. “It could be a long-term oscillation, and we can’t extend the trend into the future.” However, he notes that there was a continuous trend rather than a small number of sharp jumps.

The greater mixing of the atmosphere and ocean surface that results from increased winds and waves will be incorporated into climate models to make them more accurate.

Average annual increases in wind speed were 0.25–0.5%, but the rises in the most extreme speeds were 0.75% per year. “Today the average height of the top 1% of waves off south-west Australia’s coastline is around 6 metres. That’s over 1 metre higher than in 1985,” Babanin says.

This may force a rethink on the safety of ocean-based structures and the need for increased control measures against coastal erosion.

Unfortunately, Babanin doesn’t think it will be a boon for wave power producers. “Engineering difficulties are not limited by inadequate energy in the waves,” he says. “They’re limited by the ability of structures to capture that energy.”