A surfer rides a large wave at Tamarama. Photo: Jon Reid
Ocean wind speeds and wave heights around the world have increased significantly over the past quarter of a century, according to Australian research that has given scientists their first global glimpse of the world's rising winds and waves.
Published in the journal Science today, the research – the most comprehensive of its kind ever undertaken – used satellite data collected from 1985 to 2008.
It shows the extreme wave height off the coast of south-west Australia today is six metres on average, more than a metre higher than in 1985.
"That has all sorts of implications for coastal engineering, navigation and erosion processes," said Alex Babanin, an oceanographer at Swinburne University of Technology, Melbourne, and co-author of the paper.
However, there are greater uses for the data compiled by Professor Babanin, his Swinburne colleague Stefan Zieger and the Australian National University vice-chancellor, Ian Young.
To date scientists have largely focused on temperature as an indicator of climate change. But climate is about much more than temperature, as winds and waves control the flux of energy from the atmosphere to the ocean.
"Scientifically, this is another set of environmental properties which can be used as indicators of what is happening to the climate," Professor Babanin said. "Temperature changes the global patterns of the pressure, pressure defines the winds, winds define the waves. It's all connected."
The trio established that between 1985 and 2008, global increases in wave height were most significant for extreme waves – large spontaneous waves. They increased in height by an average of 7 per cent in the past 20 years. In equatorial regions the rise was 0.25 per cent a year, while in higher latitudes the rise was up to 1 per cent a year. The mean wave height also increased, but to a lesser degree.
When analysing extreme wind speed data over the world's oceans, the researchers found they increased by 10 per cent in the past two decades, or by 0.5 per cent a year.
Professor Babanin said waves were generated by wind. However, the data show the lift in wind speed was greater than wave height increase.
He said he doubted the 23 years of data could be immediately used to forecast future wind and wave conditions.
"These are the environmental properties which can be used as indicators for the climate behaviour along with the other properties, such as temperature and precipitation, and extrapolations have to be made with caution," he said.