Seeking a Climate-Change Signal in Wind Waves

Regional trends in wave height are driven by local winds and traveling swells. In the North Pacific, wind-driven waves dominate. But the record of wave observations is too short to tell us much about the role of climate change in wave-size trends.

That’s why a German and Danish team of researchers approached the question a different way — using state-of-the-art computer models to better understand how ocean waves respond to various climate scenarios. Mikhail Dobrynin and colleagues found that different regions of the ocean respond differently to climate change, as reported in a recent study published by the American Meteorological Society.

Over the next five decades, the researchers detect climate-change signals in wave-height trends in 60 percent of the global ocean area. In some areas — including the North Atlantic, equatorial Pacific, and Southern Ocean — climate-change fingerprints were detectable as early as the current decade (2010-20). In other regions, however, climate-change signals were hardly detectable. This was true for the North Pacific, which has high variability. And in some basins and over some time periods, the trends were downward.

The team simulated wind speed, swells and wave height over the global ocean using a global wave model “forced” by winds and sea-ice extent. This they compared to an “unforced” or control climate to establish “natural” variability. They ran simulations for the historical period (1850 to 2010) “forced” by observed greenhouse emissions, and for the future period (2010 to 2100) “forced” by a high, business-as-usual emissions scenario. Then they computed linear trends over time periods ranging from one to 50 years, and compared trends from the “forced” simulations with the range of simulated natural variability. They estimated the year in which a climate change trend (either positive or negative) significantly deviated from natural variability.

Although their results suggest that an upward trend in wave height should be detectable by the 2030s over a small swath of the Pacific Ocean in the vicinity of the Northwest, in our editorial opinion, the use of a single global model greatly underestimates the uncertainties (as the researchers themselves point out). Further research may show that changes in wave heights off the Northwest coast won’t be detectable until late 21st century. Preparing Pacific Northwest coastal communities for impacts from increasing wave heights and sea-level rise is active work for CIRC researcher Peter Ruggiero (see CIRCulator, October 2014, Issue 9).

Citation: Dobrynin, M, J. Murawski, J. Baehr, & T. Ilyina (2015) Detection and Attribution of Climate Change Signal in Ocean Wind Waves. J. Climate28, 1578–1591. doi: 10.1175/JCLI-D-13-00664.1
Photo Caption: North Pacific storm waves as seen from the NOAA M/V Noble Star, Winter. (Photo Credit: National Oceanic and Atmospheric Administration.) 

At OCCRI since 2011, Meghan Dalton works as CIRC’s project manager. A trained climate researcher with a BA in Mathematics from Linfield College and an MS in Atmospheric Science from Oregon State University, Meghan has worked closely with several Northwest communities working on Community Adaptation, including the water provider Seattle Public Utilities on the PUMA project. Meghan has worked as the lead on several regional climate assessments, including “Climate Change in the Northwest: Implications for Our Landscapes, Waters, and Communities” and “The Third Oregon Climate Assessment Report.”


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