Those who drove through the Southern Marin interchange at Highways 101 and 1 late Tuesday morning may have witnessed California's future.
The ocean and bay are getting closer.
This week, California will experience the highest tides of the year, peaking on Thursday morning in a condition known as "king tides." At 9:45 a.m. Wednesday, 10:34 a.m. Thursday and 11:24 a.m. Friday some of the year's highest tides — 7 feet and above, about a foot higher than normal — will hit Marin's shorelines.
Water will lap high in Corte Madera, along Richardson Bay and at Gallinas Creek just north of China Camp, among other spots in the county. A high tide already washed over the highway junction Tuesday near the Manzanita Park 'n Ride lot, forcing Caltrans to close some on- and off-ramps to Highway 101.
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.
"People can get out in their own communities and look at what sea level rise would look like," said Heidi Nutters, of the San Francisco Bay National Estuarine Research Reserve, based in Tiburon, who is leading a project to document the high water. "It is a way to learn and have people find ways to take action."
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.
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.
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 huge shoreline swaths of Marin, including Hamilton Field, Highway 37 and the Tamalpais Valley under water. The bay would push all the way to Highway 101 in parts of Novato and water would cover low-lying areas of Mill Valley, Sausalito and Tiburon, among other areas.
San Francisco International Airport, parts of San Jose and the East Bay could also be under water.
For more information about the photo project, go to www.californiakingtides.org.