Study finds wind speeds on the rise
By Carl Holm for ABC Science Online
http://www.abc.net.au/news/stories/2011 ... ion=justinWind speeds and wave heights over the world's oceans have been steadily
increasing for the last quarter of a century, a new long-term study shows.
The researchers at Swinburne University of Technology in Melbourne say the trend
could also have an effect on the transfer of energy between the sea and the
atmosphere - one of the great unknowns in climate change calculations.
The study, published today in Science Express online, uses 23 years of satellite
altimeter data taken from 1985 to 2008 to show that wind speeds over the oceans
have been steadily increasing.
The areas which show increased wind speeds in the study also show increased wave
heights.
Professor Ian Young, the lead author on the paper, says the study shows that the
largest increases are happening in extreme conditions.
"Extreme wind speeds have increased over most of the globe by approximately 10
per cent over the last 20 years, or 0.5 per cent every year," he says.
"Extreme wave heights have increased by an average of seven per cent over the
last 20 years."
"Off the southern coast of Australia, the highest one per cent of waves has
increased in height from approximately five meters to almost six meters."
Rising faster in higher latitudes
The researchers say average wind speeds over most of the world's oceans have
also increased, by at least 0.25 per cent per year.
The trend is stronger in the southern hemisphere than the north; and the rate of
increase is greater in extreme conditions, with wind speeds over the oceans
rising by at least 0.75 per cent per year.
Windier conditions might be expected to create higher waves, the researchers
say. But while they observed that at higher latitudes the heights of the largest
waves seemed to be increasing, they found no statistically significant increase
in average wave height globally.
Co-author Professor Alexander Babanin says it is unclear yet how, or if, the
trend relates to global climate change.
"All we can say is that there is an overall trend, but extrapolating that into
the future has to be done with caution," he said.
But he says the record adds an important and often overlooked variable to
climate change studies.
"If we talk about climate, usually we talk about temperature changing, we talk
often about precipitation; but we talk much less about the winds and the waves,"
he said.
"They are environmental indicators of changes in the climate just as the
temperature and precipitation and other parameters in the air-sea system."
Professor Babanin says the data are potentially useful because they can provide
independent validation and verification of what happens to the climate.
"Suppose it's the case that the temperature is rising globally. It will not do
that uniformly, because of land influences, because of the ocean circulation,"
he said.
"The ocean will be warmer in some parts and colder in other parts. That creates
pressure differences and that creates winds.
"When you change the pressure patterns and if the temperature difference is
getting bigger, pressure differences are getting bigger, the winds will perhaps
grow higher, and the patterns of the winds may change."
Professor Babanin says it is the first study to deliver such a complete picture.
Previous studies had relied on observations from ships at sea and wave buoys,
which meant most data was collected close to shore and in major shipping lanes.
"So in terms of the uniform and consistent global coverage this is the first one
of its kind," he said.
