For many years, the specter of sea-level rise has hovered over residents of Marin – southern Marin in particular – with no shortage of first-hand visuals, like the flooded Mill Valley-Sausalito Multiuse Path along the 106-acre Bothin Marsh, which has long been one of the most popular paths in the entire Bay Area, with more than a half-million recreational users between March and November each year, according to the annual WalkBikeMarin Path Counts.

Sea Level Rise in Marin County is a when – not if – fact of life. Climate experts estimate that by 2100, sea levels could rise by around 70 inches and that the frequency, intensity and flood-effects of storms will increase. And Bothin Marsh could will lose a significant amount of vital wetland habitat by 2030.

Those discussions haven’t always had a firm sense of the cost associated with sea level rise in our region.

Dana Brechwald, a climate official at the San Francisco Bay Conservation and Development Commission, stepped into that breach last month, telling the Marin County Board of Supervisors that Marin County is facing about $17 billion in expenses to protect itself from the rising sea, the second highest cost estimate in the Bay Area, according to the Marin Independent Journal.

Senate Bill 272, which Gov. Gavin Newsom signed into law in July, requires coastal counties to develop a plan to prepare for sea-level rise by Jan. 1, 2034.

“Alameda and Marin County have the highest cost estimates,” Brechwald said, “which aligns with their vulnerability to sea-level rise.”

Marin County has more than 70 miles of coast and 40 miles of bay shoreline, much of which is low lying and subject to direct tidal flooding as well as creek and storm flooding.

Brechwald said that according to a recent National Oceanic and Atmospheric Administration study, San Francisco Bay has risen 8 inches since 1900 with an additional 12 to 32 inches predicted by 2050 and up to 10 feet or more by the end of the century.

“This trend of rising shorelines is not just continuing,” she said, “it’s accelerating.”