If you head down the beach this week, or wander along the edges of San Francisco Bay, you may just be witnessing California's future.

The ocean is getting closer.

This week, California will experience the highest tides of the year, peaking on Thursday morning in a condition known as "king tides." Beaches will temporarily disappear. Water will lap high on docks at marinas.

The gravitational tug of the moon and sun, not climate change, is responsible for the extreme tides. But volunteers with cameras across the state are using the event to document what California could look like in the coming decades as the warming earth continues to raise sea levels.

When people see the high tides this week, scientists hope many will make that connection.

"You can read something, but when you see it firsthand, it's more powerful," said Gary Griggs, director of the Institute of Marine Sciences at UC Santa Cruz. "When you see a place you know, when you see a king tide and say, wow, it's six inches from the San Francisco International Airport runway, you realize this is real. It's not just a model."

King tides occur several times a year, although this week's are the biggest of 2012.

Luckily for coastal residents, this week's tides aren't expected to cause significant flooding because they are happening during relatively calm weather.

"Flooding would be a concern if we had a storm system coming through," said Matt Mehle, a meteorologist with the National Weather Service in Monterey.


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Instead, the rising water will offer a teachable moment, scientists say. Already, the ocean off California has risen 8 inches in the past 100 years. As the earth warms, polar ice melts, and the warmer ocean water expands, increasing sea level. That rate of sea level rise is accelerating.

A National Academy of Sciences report in July found that, relative to sea levels in 2000, the California coast south of Cape Mendocino is projected to experience sea level rise of 1.5 inches to 11.8 inches by 2030, and 4.7 inches to 24 inches by 2050, and 16.5 inches to 65 inches by 2100.

The latter numbers -- more than a 5-foot increase -- would put large sections of coastal California underwater, including Bay Area airports, Treasure Island and Silicon Valley businesses, such as Oracle, particularly during major storms, requiring tens of billions of dollars in sea walls and other defenses.

The massive flooding of lower Manhattan and New Jersey's shoreline from Hurricane Sandy earlier this year have illuminated the threat, scientists say.

"Sandy brought us to our senses," Griggs said. "Because of the drought this year, because of the loss of arctic ice, people are finally understanding climate change."

Along with the high tides this week -- from a few inches to several feet higher than normal, depending on the location -- there are also extremely low tides.

At Half Moon Bay on Thursday, for example, the high tide will be plus-6.8 feet at 9 a.m., or 6.8 feet above the historic average daily low tide. The ocean will then fall 8.5 feet by 5 p.m. that day to a minus-1.7 feet tide, which should make for some great tide pool exploring.

"It's going to be extreme on both ends," said Mark Sponsler, of Castro Valley, who serves as surf forecaster for the Mavericks Invitational Surf Contest. "Go down in the morning, check it out, then show up about 3 p.m. and see how low it goes. You'll notice a distinct difference."

The tides will be as high as plus-10.1 feet Thursday morning at the Dumbarton Bridge, plus-8.7 feet at San Leandro Marina and plus-6.7 feet in Santa Cruz. They're higher in the bay, Griggs said, because the bay acts as a cul-de-sac, where water surges in and piles up.

Ironically, high tides often don't mean big waves. Tides come from the gravitational pull of the moon, which causes the water in the ocean to bulge. Waves come from wind and storm events. This week, waves along the Northern California coast are fairly mild because there are no major storm systems.

"From a surfing perspective, the preference is lower tides," Sponsler said. "You get too much water, and the waves either won't break or they don't have good shape."

For some, the big tides are a chance to enlist the public in a giant science project.

As they have for the past two years, a coalition of government agencies and nonprofit groups is asking the public to take photographs Wednesday and Thursday around California to document the high water -- preferably of the same place at high tide and low tide.

The project, called the California King Tides Initiative, posts the photos online. Since 2010, nearly 500 photos from 28 California cities have been posted to the site showing king tide events in California. They have been featured at the Monterey Bay Aquarium, California Academy of Sciences and other prominent places. Similar "citizen science" photo projects around king tides have been organized in Oregon, Washington, British Columbia and Australia.

"We are trying to create a living archive of images we can all use to communicate about sea level rise," said the initiative's coordinator, Heidi Nutters, of the San Francisco Bay National Estuarine Research Reserve, based in Tiburon. "Climate change is not only about polar bears in the arctic. It's about what's happening on our coasts right now and today."

For more information about the photo project, go to www.californiakingtides.org.

Paul Rogers covers resources and environmental issues. Contact him at 408-920-5045. Follow him at Twitter.com/PaulRogersSJMN.