SAN JOSE, Calif. - Those who head down to California's beaches this week, or wander along the edges of San Francisco Bay, may just be witnessing the state'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 first hand, it's more powerful," said Gary Griggs, director of the Institute of Marine Sciences at the University of California, Santa Cruz. "When you see a place you know, when you see a king tide and say, 'wow it's 6 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, Calif.

Instead, the rising water will offer a teachable moment, scientists say. Already, the ocean off California has risen 8 inches in the last 100 years. As the Earth warms, polar ice melts and the warmer ocean water expands, increasing the 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 San Francisco Bay Area airports and Silicon Valley businesses, 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 has illuminated the threat, scientists say.

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

As it has for the last 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.