John Bruno, Skeptical Science: More wind, bigger waves, changing marine ecosystems (wave height, wind and "storminess" have been increasing at sea and along the coasts over the last several decades, at least in non-tropical regions)

More wind, bigger waves, changing marine ecosystems

by John Bruno, Skeptical Science, April 13, 2011

There has been lots of science and even more debate about how anthropogenic climate change will alter the frequency and intensity of cyclonic storms. But you don't hear much about how ocean wind and waves in general are changing and how this might impact marine ecosystems. Some new work is beginning to address this important topic.   

Lets start with the physical changes.

A paper recently published in ScienceExpress (Young et al. 2011) reports that ocean wind and waves increased substantially over the last two and a half decades. The authors used satellite altimeter measurements to test for trends in wave height from 1985 to 2008 and wind speed from 1991 to 2008. There was a positive trend in average wind speed and wave height, especially at higher latitudes (note the weaker trends in equatorial regions are not statistically significant): 

Figure. 1. Colour contour plots of mean trend (% per year). Wind speed is shown at the top and wave height at the bottom. From Young et al. (2011). 

The change in significant wave height is more pronounced when you look at the 99 percentile (the very biggest waves):

Fig 2. Colour contour plots of the 99th percentile trend (% per year). Wind speed is shown at the top and wave height at the bottom. From Figure 3 in Young et al. (2011). 

The Young et al. (2011) study mirrors a number of smaller scale studies based on more direct measurements or estimates of wave height trends. For example, Bromirski et al. (2003) used tide gage data from San Francisco to assess "meteorologically forced nontide residuals" (NTR), i.e., ‘‘storminess’’ from 1858 to 2000 along the central california coast. They found an increase of both degree and duration since 1950, consistent with other local and regional studies:

Figure 3. (b) Cumulative extreme NTR (exceeding the 98th percentile level of 11.5 cm for the entire hourly NTR time series) during winter months (Dec–Mar), with its 5-yr running mean (red line). Least squares trend estimates for the entire winter record and since 1948 (dashed lines). (c) Cumulative extreme winter hours (blue line) and events (red line). Dashed blue line indicates less than 90% of the hourly data were available, indicating that these periods may be underestimated. Times of strong, moderately strong, and very strong El Ninos (Quinn & Neal 1987) are indicated by green dots. From Figure 6 in Bromirski et al. (2003).

So, the picture emerging from the complete scientific body of evidence is that wave height, wind and "storminess" have been increasing at sea and along the coasts over the last several decades, at least in non-tropical regions. Although in some cases the record is fairly long (for direct physical measurements), it isn't really long enough to strongly attribute these changes to ACC. Furthermore, predicting changes in mid-latitude or "extra-tropical" storms (such as would have been measured in the Bromirski et al. study) is tricky. But regardless of the cause, why should we care? 

One reason is that by impacting habitat-forming "foundation" species, physical disturbance, especially by waves, plays a hugely important role in structuring coastal marine communities. For example, Byrnes et al. (2011) just published a paper that assessed how changes in the frequency of coastal storms would affect kelp forest communities off of the central California coast.

Giant kelp (Macrocystis pyrifera) are the "foundation species" of the California kelp forest communities. This species creates the biotic structure that thousands of other organisms depend on. Other examples of marine foundation species are corals, oysters, seagrasses and mangroves. Trees are a great terrestrial example. Due to their size, foundation species are often susceptible to physical disturbances, such as waves, that can dislodge and remove them. 

The authors used structural equation modeling (SEM) to statistically relate the impacts of storms on kelp forest community structure (i.e., in situ measurements of invertebrate species richness, kelp cover, fish abundance, etc., collected with SCUBA by the Santa Barbara coastal LTER). They also compared the predictions of the SEM (depicted in Figure 4) with the effects of experimental kelp removal (from 2,000 m² plots!) on kelp forest communities. The SEM and the experimental manipulation both found that decreased kelp cover leads to a decrease in the diversity and complexity of kelp forest food webs. 

If large storms remain at their current annual frequency (roughly one major kelp-removing storm every 3.5 years), periodic storms help maintain the complexity of kelp forest food webs. However, if large storms increase in annual frequency and begin to occur year after year, kelp forest food webs become less diverse and complex as species go locally extinct. The loss of complexity occurs primarily due to decreases in the diversity and complexity of higher trophic levels. Our findings demonstrate that shifts in climate-driven disturbances that affect foundation species are likely to have impacts that cascade through entire ecosystems. 

Figure 4. Path diagrams showing how algal, sessile invertebrate, and mobile species richness are associated with winter wave disturbance from storms and the abundance of kelp in the past year. Results are from a fitted structural equation model that adequately reproduces the observed covariance matrix. Solid paths are statistically different from 0 at P 0.05. Dashed paths are not. Path widths are proportional to standardized regression coefficients (shown next to each path). For clarity, some path coefficients are included in variable boxes rather than being drawn directly on the diagram. From Figure 4 in Byrnes et al. (2011). 

Countless studies have investigated/documented the impacts of storms and other physical disturbances on kelp and many other marine foundation species. The effects are not always negative; a moderate level of disturbance can help maintain the diversity of foundation species and of community inhabitants by preventing competitively dominant species from excluding their neighbors (via the monopolization of resources) and by maintaining a "patch mosaic" of microhabitats that promotes diversity. 

One novel aspect of this work, in addition to combining a field manipulation with a statistical data-crunching approach, was the focus on the entire food web rather than just one trophic level. Yet this study builds on decades of work indicating how sensitive coastal communities are to intense disturbances. If storms, wind and waves are causally linked with ACC and do continue to increase, I think there is little question that we will see direct effects on marine ecosystems and the services they provide to people.  

Beyond that, you could imagine a variety of other ecological and socioeconomic impacts of increased ocean wind, waves and storminess. For one, this could result in more ocean mixing and less stratification, thereby enhancing primary production (by supplying more nutrients for phytoplankton in generally nutrient-poor surface waters). You might also expect greater coastal erosion (which is compounded by sea level rise) and effects on shipping, ocean oil refineries, wind farms, etc.

Ocean winds are not exactly the first thing you think about when the topic of climate change comes up. Yet if they do continue to increase, the knock on effects will be large and costly. Yet another reason I like to call it "Ocean Change" rather than "Climate Change." 

http://www.skepticalscience.com/more_wind_and_waves.html

Average wind speeds and wave heights have been rising on the world’s oceans over the last quarter century, a trend that could portend more intense storms, hurricanes, and cyclones, more damage to infrastructure and shorelines (study in Science by Ian Young et al.)

WIND SPEEDS INCREASING
ON WORLD’S OCEANS, STUDY SAYS

e360 digest, environment360, March 25, 2011


Average wind speeds and wave heights have been rising on the world’s oceans over the last quarter century, a trend that could portend more intense storms, hurricanes, and cyclones, according to a new study. Using satellite altimeter data from 1985 to 2008, Australian researchers calculated that wind speeds increased 0.25-0.5% per year, and overall had increased 5-10% during that time. The most pronounced increases were observed during extreme wind events — in comparison with mean conditions — which increased about 0.75% annually, according to the study, published in the journal Science. Ian Young, a professor at the Australian National University at Canberra and lead author of the study, said it is unclear whether it is a temporary phenomenon or the result of global climate change, although he added, “If we have oceans that are warming, that energy could feed storms, which increase wind speeds and wave heights.” 


http://e360.yale.edu/content/digest.msp?id=2868

Study finds wind speeds rose over world's oceans, wave heights increased, generating rougher seas, possibly leading to positive feedback in the form of increasing water vapor in the air

Study finds wind speeds rose over world's oceans

by Randolph E. Schmid, AP Science Writer, March 24, 2011

WASHINGTON – During the last quarter-century, average wind speeds have increased over the world's oceans, as have wave heights, generating rougher seas, researchers reported in a study published online Thursday.

Since faster winds cause more evaporation, the increase could lead to more water vapor in the air, compounding any increase from global warming and providing added moisture for rain. Generally, that means a higher chance for rainfall.

Researchers led by Ian Young of Swinburne University of Technology in Australia report in the journal Science that over a 23-year period, average wind speed over the oceans rose by 0.25% per year.

The proportion of increase in wave height was less than for wind speed, the researchers noted, while the increase for extreme winds was more than for average winds.

The researchers said the higher winds aren't necessarily the result of global warming.

But Eugene S. Takle, director of the climate science program at Iowa State University, and not part of Young's research team, noted that evaporation rises with higher wind speeds, so the result would be more moisture in the air even without global warming. And the warming shown in many studies would also increase evaporation.

Just two years ago, Takle and colleagues published a study of wind speeds over land showing a decrease, rather than the increase Young's team found in its measurements from satellites and buoys. Young studied satellite records from 1985 to 2010, though records for 1990-1991 were not available because of satellite problems.

"I don't think these results provide a clear contradiction to our findings of declining wind speeds over land, since measurements are made in different environments," said Takle.

He noted that the day-to-night changes in temperature are different over land than over water and the boundary layer — the portion of the atmosphere that most closely interacts with the surface — is generally thicker over land than water.

http://news.yahoo.com/s/ap/20110324/ap_on_sc/us_sci_restless_wind

I. R. Young, S. Zieger & A. V. Babanin, Science (2011), Global trends in wind speed and wave height

Science, published online March 24, 2011; doi: 10.1126/science.1197219

Global trends in wind speed and wave height

1. I. R. Young, 
2. S. Zieger, and 
3. A. V. Babanin

Abstract

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 compared to the mean condition.

Link to abstract:  http://www.sciencemag.org/content/early/2011/03/23/science.1197219.abstract

Ocean waves getting bigger, and stronger; Rogue waves challenge pilots; experts differ on whether climate change is the cause

Ocean waves getting bigger, and stronger

Rogue waves challenge pilots; experts differ on whether climate change is the cause.

by Les Blumenthal, McClatchy Newspapers, November 12, 2010

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  Jackie Burns looks through a spotting scope at the water off Cape Disappointment in Washington state. There's a "lot of reading of tea leaves" about the cause of bigger and stronger ocean waves, said Oregon State University professor Peter Ruggiero. BRIAN HARRISON - TACOMA NEWS TRIBUNE/MCT

WASHINGTON -- It's one of the most treacherous stretches of water in the world, where 1 million cubic feet of water a second collides with 20- or 30-foot ocean swells over a four-mile stretch of shifting sand.

A small band of pilots braves often-treacherous conditions to guide ships across the Columbia River Bar.

The pilots who work the "Graveyard of the Pacific" have a deep respect for the relentless forces they face daily as they ride out to tankers, bulk carriers, car carriers, and cargo and passenger ships standing offshore. They commute in 72-foot self-righting boats that can roll over 360 degrees as winter gales and sometimes hurricane-force storms blast out of the North Pacific.

The pilots also confirm what marine scientists have just started talking about: Ocean waves are becoming bigger and more powerful, and climate change could be the cause.

"We've been talking about it for a couple of years now," said Capt. Dan Jordan, who served in the merchant marine for 30 years before becoming a Columbia River Bar pilot. "Mother Nature has an easy way of telling us who is in charge."

Using buoy data and models based on wind patterns, scientists say that the waves off the coast of the Pacific Northwest and along the Atlantic seaboard from West Palm Beach, Fla., to Cape Hatteras, N.C., are steadily increasing in size. And, at least in the Northwest, the larger waves are considered more of a threat to coastal communities and beaches than the rise in sea level accompanying global warming is.

Similar increases in wave height have been noticed in the North Atlantic off England.

Unclear is whether the number and height of "rogue" waves beyond the continental shelf have increased. The existence of such freak waves, which can reach 100 feet or more in height and can swamp a large ship in seconds, wasn't proved until 2004, when European satellites equipped with radar detected 10 of them during a three-week period. According to some estimates, two merchant ships a month disappear without a trace, thought to be victims of rogue waves.

"Obviously, this is an issue we are interested in," said Trevor Maynard of Lloyd's of London's emerging risk team, which tracks global climate-change developments. "We are seeing climate change fingerprints on a lot of events."

Since the mid-1970s, buoy data show the height of the biggest waves off the Northwest coast has increased an average of about four inches a year, or about 10 feet total, according to Peter Ruggiero, an assistant geosciences professor at Oregon State University and the lead author of a study published recently in the journal Coastal Engineering.

Ruggiero and his colleagues also estimated how high a 100-year wave might be. These would be the largest waves expected to come along every 100 years. The estimate has increased 40% since the 1970s, from 33 feet to 46 feet. Some calculations estimate a 100-year wave might be 55 feet high, taller than a five-story building.

"We are assuming the trends will increase in the future," Ruggiero said.

The future already may be here, however.

Jordan, the Columbia River pilot, said a 44-foot wave was recorded off the river in October. In a major spring storm in 2007, a 54-foot wave was recorded.

"After that the buoy quit recording," Jordan said.

On the East Coast, a yet-to-be-published study also has showed that average wave heights have been increasing, by a couple of centimeters or so a year.

"The averages aren't very exciting," said Peter Adams, an assistant professor in the University of Florida's Department of Geological Sciences who used wind data from the past 20 to 30 years to develop a wave height model. "Given that there are 3 million waves a year, one wave every 10 seconds, it's not so alarming."

Adams said he finds it startling that the height of the biggest waves has increased nearly a foot in 10 years.

"In a lifetime, that can be profound," he said.

A scientific debate is raging over what's causing the increase in wave size. Possible causes include changing storm tracks, higher winds and more intense winter storms -- all signs of global climate change.

"While these increases are most likely due to Earth's changing climate, uncertainty exists as to whether they are the product of human-induced greenhouse warming or represent variations related to natural multi-decadal climate cycles," Ruggiero's study said.

Among the weather phenomenon that could be affecting wave heights in the Pacific, Ruggiero said, are El Nino -- warmer surface temperatures in the tropical eastern Pacific -- and the Pacific Decadal Oscillation -- 20-30-year patterns of warmer or cooler surface temperatures in the Pacific.

"There is a lot of speculation, a lot of reading of tea leaves," he said.

Others are skeptical about any link to climate change.

Richard Seymour, the head of the Ocean Engineering Research Group at the Scripps Institution of Oceanography in California, said any connection between increased wave height and climate change is tenuous. In fact, Seymour said, there aren't enough data on wave heights to provide the "statistical reliability" to predict any trends.

Seymour and others said too little is known about the oceans.

"It always struck me as odd we know more about the surface of Mars than the floor of the Pacific Ocean," he said.

Read more: http://www.charlotteobserver.com/2010/11/14/1836887/ocean-waves-getting-bigger-and.html#ixzz15IgH3j00