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Acknowledgments: This work was supported by a
Grant-in-Aid for Scientific Research (B) (Japan Society
for the Promotion of Science). We thank Central Glass
Co., Japan, for a generous gift of BrF3.
Supporting Online Material
Materials and Methods
Figs. S1 to S12
Tables S1 and S2
14 December 2010; accepted 4 March 2011
Global Trends in Wind
and Wave Height
I. R. Young,* S. Zieger, A. V. Babanin
Studies of climate change typically consider measurements or predictions of temperature over
extended periods of time. Climate, however, is much more than temperature. Over the oceans,
changes in wind speed and the surface gravity waves generated by such winds play an
important role. We used a 23-year database of calibrated and validated satellite altimeter
measurements to investigate global changes in oceanic wind speed and wave height over this
period. We find a general global trend of increasing values of wind speed and, to a lesser
degree, wave height, over this period. The rate of increase is greater for extreme events as
compared to the mean condition.
Oceanic wind speed and wave height help to control the flux of energy from the atmosphere to the ocean (1) and upper
ocean mixing (2). Thus, they substantially influence the mechanisms of air-sea interaction (3).
Previous attempts to investigate trends in oceanic
wind speed and wave height have used ship observations (4–8), point measurements (9), numerical modeling (10–15), or satellite observations
(16). Almost all of these studies are regional
rather than global. Although there is a range of
results, many studies show an increasing trend in
significant wave height, particularly in the North
Atlantic and North Pacific, often correlated with
interannual variations such as the North Atlantic
Oscillation. Careful ship observations (4–6) also
show waves locally generated by the wind (hereafter
referred to as wind-sea) and swell behaving quite
differently and that there exist quite different trends
in wind speed and wave height. The present analysis
uses recently developed satellite altimeter data sets
to carefully investigate such trends on a global scale.
Satellite-based systems provide an alternative
to visual or in situ measurements of oceanic wind
Swinburne University of Technology, Melbourne, Victoria,
*To whom correspondence should be addressed. E-mail:
speed and wave height, using a variety of instruments, including altimeters, scatterometers, and
synthetic aperture radar, providing global coverage of wind and/or waves. Of these instruments,
the radar altimeter provides by far the longest-duration record. Since the launch of GEOSAT in
1985, there exists an almost continuous (there
was a break in 1990–1991) record of measures
from a total of seven different altimeter missions.
Numerous calibrations of these altimeters have
shown that the instruments can be used to measure significant wave height, Hs ¼ 4
period. Because the seasonal cycle typically is
large, care must be exercised in determining trend
information from the data set [supporting online