Image: Erosion along San Francisco beach
Jeff Hansen  /  USGS
Battering waves beat up this stretch of road along Ocean Beach in San Francisco, Calif., within three weeks in January 2010.
msnbc.com
updated 7/13/2011 4:54:03 PM ET 2011-07-13T20:54:03

Severe erosion along the West Coast during the winter of 2009-2010 offers a look at, and lessons for, a warming world with rising sea levels, a new study finds.

A natural El Nino cycle that warms the Pacific Ocean produced those severe conditions, but computer models suggest that similar damage could come from sea level rise tied to human-caused greenhouse gases.

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"If these trends continue," U.S. government and academic experts wrote in their study, "the combination of large waves and higher water levels, particularly when enhanced by El Ninos, can be expected to be more frequent in the future, resulting in greater risk of coastal erosion, flooding, and cliff failures."

Lead author Patrick Barnard, a coastal geologist with the U.S. Geological Survey, told msnbc.com that the study serves as a platform "to understand the broad coastal impact of conditions we are likely to experience more frequently in the future."

In California, the researchers found that winter wave energy was 20 percent above average for the years dating back to 1997, resulting in shoreline erosion that exceeded the average by 36 percent.

"The stormy conditions of the 2009-10 El Nino winter eroded the beaches to often unprecedented levels at sites throughout California," Barnard said in a USGS statement released with the study.

San Francisco's Ocean Beach saw some of the most severe erosion. Its shoreline retreated 184 feet — 75 percent more than in a typical winter — taking out a lane of a major roadway. Sites in San Diego, Santa Barbara and Ventura also saw significant erosion.

In its statement, the USGS warned of worsening erosion as warming melts ice sheets and glaciers, and potentially creates more severe storms.

"When combined with still higher sea levels expected due to global warming, and potentially even stronger winter storms," it stated, "these factors are likely to contribute to increased rates of beach and bluff erosion along much of the U.S. west coast, producing regional, large-scale coastal changes."

Story: Crumbling cliffs don't deter these residents

Barnard noted that El Ninos can raise winter water levels by 4-8 inches along the West Coast. Given the projected acceleration of global sea level rise that has been around a tenth of an inch annually, he said, "it is likely we will hit that level in the next few decades" along the coast due to global warming.

The study was published in the peer-reviewed journal Geophysical Research Letters.

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Video: Rise in sea levels accelerates

Photos: Warming refugees?

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  1. Lifestyle changes tied to warming have already come to this corner of the world, the Inupiat village of Shishmaref. Temperatures that have risen 15 degrees Fahrenheit over the last 30 years are melting the sea ice that has helped shield the shore from erosion, and thawing the permafrost on which the village was built. Dozens of other Alaskan coastal towns face similar problems if warming worsens. (Gabriel Bouys / AFP/Getty Images) Back to slideshow navigation
  2. One of Shismaref's newest residents takes shelter. The 2000 census counted 562 residents, who face evacuation and the loss of their traditional way of life. Shishmaref can't afford to relocate on its own and no state or federal agency has come forward with funds. (Gabriel Bouys / AFP/Getty Images) Back to slideshow navigation
  3. Shishmaref resident Elisabeth Nayokpuk dries caribou skins. Town leaders hope to relocate residents to more stable ground. (Gabriel Bouys / AFP/Getty Images) Back to slideshow navigation
  4. Johnny Weyiouamma Sr. watches his wife, Arthie, prepares caribou meat delivered by their son Perry for winter. Many communities like Shishmaref rely on the meat, but caribou could see their foraging grounds on the tundra shrink as vegetation and forests migrate north due to warming. (Gabriel Bouys / AFP/Getty Images) Back to slideshow navigation
  5. Some property, including this home, in Shishmaref has been destroyed by erosion tied to stronger waves and the loss of sea ice that served as a buffer. The town is on a barrier island a quarter mile wide and three miles long. Annual erosion has averaged 3 to 5 feet in recent years, though three large storms since 1970 ate up to 125 feet of land in places. A 200-foot seawall has been built along part of the shoreline, but it's estimated that 3,400 feet of beachfront needs protecting. (Gabriel Bouys / AFP/Getty Images) Back to slideshow navigation
  6. Shishmaref artist Herbie Nayokpuk works on his Eskimo hunter sculptures, which he sells as souvenirs. Hunting has become precarious as snow and sea ice soften up, making journeys more treacherous. (Gabriel Bouys / AFP/Getty Images) Back to slideshow navigation
  7. Shishmaref sits on a layer of permafrost, or frozen ground, that is beginning to thaw. When strong waves strike the coast, the thawing ground erodes much more quickly. (Gabriel Bouys / AFP/Getty Images) Back to slideshow navigation
  8. Shishmaref hunters like Johnny Weyiouamma rely on boats to go after seals. A 2003 storm hit their fleet hard, swamping several boats and causing $100,000 in damage. (Gabriel Bouys / AFP/Getty Images) Back to slideshow navigation
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Interactive: Global warming: Port cities are vulnerable to rising waters

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