SAN FRANCISCO - Sometime over the next century huge shoreline swaths of Marin, including Hamilton Field, Highway 37 and the Tamalpais Valley could be under water if global warming causes the bay to rise by a meter, according to the San Francisco Bay Conservation and Development Commission.
Additionally, wild and extreme swings in the climate brought on by warming could have an impact on Marin's water supply.
Maps showing the coastal inundation were presented Wednesday at the Water Utility Climate Change Summit in San Francisco, where water officials from around the state gathered to hear information on global warming.
"This is not conjecture, it's happening here," said Will Travis, executive director of the bay commission, noting the bay has risen by 7 inches since 1900. "This isn't theory, it's reality."
The commission used a meter - a little more than 3 feet - based on the projected impact of global warming made by scientists. The time frame is 100 years, although Travis said it could occur more rapidly.
"What has not been factored in is the melting of Polar ice caps," he said. "Highway 101 near Marin City will be affected as well as other areas in Marin."
The maps show the bay pushing almost all the way to Highway 101 in parts of Novato, as well as water covering 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 as the bay rises.
Travis believes economic engines, such as the San Francisco airport, would eventually be protected by levees, but other areas might have to be abandoned.
"In some cases it may be less costly to just retreat rather than to try to protect everything," he said, adding some developed areas could be removed and wetlands created to help absorb rising water.
Travis said he prefers the term "climate change" to global warming.
"While the Earth's atmosphere will be getting warmer, some places will be getting hotter, but others will be getting cooler and the climate will become much more erratic. Some years the Bay Area will go through extended droughts. Other years we may get unusually heavy rainfall," he said.
That could prove problematic for Marin's water supply, which largely relies on rainfall collected in reservoirs on the Mount Tamalpais watershed.
"Climate models are saying there will be a greater level of variability, more severe droughts, droughts that last longer," said Marin Municipal Water District board member David Behar, who helped organize the summit in his role as a water manager with the San Francisco Public Utilities Commission. "Right now Marin is not ready for any kind of drought. Demand would also grow because of greater heat."
Assemblyman Jared Huffman, D-San Rafael, who spoke at the summit, said desalination - using bay water for municipal needs - could play a role in helping Marin in a warming world.
"Most scientists project volatility for our region. For folks that rely on snowpack, you pretty much know what temperature increases are going to do and you can project how that will impact your water supply. In our case we will see long wet periods and longer dry periods, which we have always seen, but now it will be amplified. It puts an emphasis on desal as a hedge against that volatility," Huffman said.
Paradoxically, the district has drawn up preliminary plans for a desalination plant along the bay, in an area that could become inundated with water as the bay rises.
"Shoreline inundation is a major issue for every county that rings the bay," Behar said. "We have to look at the facilities of ours and develop protections. In looking at siting facilities along the bay, such as a desal plant, we have to look at what impact sea level rise will have on them."
Paul Helliker, general manger of the Marin water district, who also attended the summit, said water use planning related to climate change needs to start now.
"We want to plan for whatever sea level rise it will be," he said. "The variability is what we are worried about. The 1976-77 was the drought of record, and yes, it could be drier. Desal is then another factor to look at."
Said Behar: "Water agencies are among the first institutions in this country that have to look at the impacts of climate change now because it is not an abstraction for us, it's actually in our planning horizons now. We have to think about impacts to water supply and demand. That is a big issue for Marin - what will demand be. How will climate variability change affect supply and demand patterns."
Contact Mark Prado via e-mail at firstname.lastname@example.org