California coastal cities should be prepared for the possibility that oceans will rise more than 10 feet by 2100 and submerge parts of beach towns, the state Coastal Commission warns in new draft guidance.

The powerful agency, which oversees most development along 1,100 miles of coast, will consider approving the guidance this fall. A staff report recommending the changes was released last week.

Earlier commission guidance put top sea-level rise at 6 feet by 2100. But according to the new report, there’s the “potential for rapid ice loss to result in an extreme scenario of 10.2 feet of sea level rise” by the end of the century.

Even without the 10-foot rise, the draft guidance cautions, as much as two-thirds of Southern California beaches “may be completely lost due to rising sea level.”

If adopted, the guidance will advise municipalities to evaluate the 10-foot scenario for planning and permitting. It’s aimed at getting cities to think differently about how they approve large projects that are likely to be in place for many years and that can’t be easily changed once built, said Madeline Cavalieri, statewide planning manager at the commission.

“What we’re saying is, look at that 10 feet of sea-level rise and think about what it means for your future,” Cavalieri said in an interview. Cities need to think long-term when planning, she said, because “we don’t want to go investing a lot of resources into developing an area that we know is going to be underwater.”

The proposed guidance comes as the commission is asking more than 40 cities and counties to spell out how they’ll adapt to sea-level rise in the planning rulebooks known as Local Coastal Programs. Those outline how jurisdictions implement provisions of the state’s Coastal Act, a law designed to protect beaches, habitats and coastal access.

The commission, which must approve the plans, has butted up against cities on issues related to the change, including sea walls. The state agency looks to limit those, arguing they block beaches from moving inland as waters rise.

Some entities that would be affected by the proposed guidance already have lodged complaints. The Port of San Diego told the commission in a letter that, “due to the current state of knowledge about the West Antarctic ice sheet” and the 10-foot scenario, “planning for such event without a greater degree of certainty is not appropriate.”

Cavalieri said, though, that the port wouldn’t be obligated to design for 10 feet of sea-level rise if the guidance were adopted.

“It may be that they build something today that is designed to withstand a lesser amount of sea-level rise,” she said, “but they should do that going in eyes wide open that this might be an area that’s vulnerable. Maybe looking at that 10 feet, there are other design options.”

The proposed new guidance incorporates information from California’s Ocean Protection Council, which last year updated projections for what the state’s iconic coastline faces in years ahead.

The OPC revisions used an analysis from scientists Helen Fricker at Scripps Institution of Oceanography at the University of California, San Diego, and Robert DeConto at the University of Massachusetts, Amherst. They warn of hydrofracture, a phenomenon that occurs when water that’s on top of ice sheets due to melting seeps into crevasses and causes them to widen. That could result in the ice sheets breaking away from grounded ice.

Hydrofracture happened once already in 2002 to the Larsen B Ice Shelf in Antarctica. The incident wasn’t catastrophic because the shelf was not holding back a lot of ice, Fricker said in an interview. But if it happened with other ice sheets in the region, she said, “then you may get a very large runaway retreat” of ice from Antarctica.

“It’s not out of the question,” Fricker said. “There’s a low probability it could happen, but it’s something we should be mindful of as we plan for the future.”

Fricker briefed California Gov. Jerry Brown (D) on that part of the OPC report last year. She said the first thing the governor asked was the elevation of the airports in Los Angeles and San Francisco.

Brown, she said, was concerned about “how quickly are we going to need to move things like airports.”

No probability for 10 feet

Last week’s draft commission guidance—based on the OPC analysis—gives several scenarios for what future sea-level rise could look like along different parts of the coast. Under the “low range” in the San Francisco area, for example, water could rise just over 1 foot by 2050 and 3.4 feet by 2100.

The medium scenario projects 1.9 feet of sea-level rise by 2050 and 6.8 feet by the turn of the century.

The OPC report, though, wouldn’t place a probability on 10 feet of sea-level rise, saying that “at this point, it is scientifically premature to estimate” the likelihood that what it called the “H++ scenario” will come to pass “and, if so, when the world will move onto the H++ trajectory.”

Asked why the state and local governments should plan for a scenario that might not happen, Kelsey Ducklow, climate change analyst at the Coastal Commission, said that “while the H++ scenario has a low probability of occurring, it is a possibility.”

“So understanding this worst-case scenario is an important factor for resilience planning, particularly for existing or planned development that would be irreparably damaged and would have significant environmental consequences,” she said in an email. Even if new development isn’t designed to the 10-foot standard, she said, “it is important to evaluate so that decisions can made with a full understanding of the risks to the development and the environment.”

Some residents of coastal California cities already are rejecting sea-level rise projections, even those well below the 10-foot scenario.

“Some of the climate change exaggerations of 3 feet of sea-level rise is equal to fearmongering,” Jim Steele, with the Community Working Group on Sea Level Rise in Pacifica, said at an August meeting on that city’s possible adaptation plans.

Steele said that sea level has risen about 8 inches over the last century, a rate of about 2 millimeters a year. If that rate continued, he said, it would take 144 years to rise 1 foot.

Others at the meeting pushed back, saying new climate science indicates faster sea-level rise.

James Jackson with Environmental Science Associates, a consultant in Pacifica, responded that the city’s draft adaptation policy aligns actions with “the actual amount of observable sea-level rise.”

Pacifica, which is south of San Francisco, already has seen coastal bluffs deteriorate to the point where three apartment buildings and a house perched on the edge were deemed unsafe and eventually demolished. City officials say El Niño storms contributed to that cliff erosion. El Niño, which occurs when temperatures in the Pacific Ocean climb above normal, often brings heavy precipitation.

Jennifer Savage, California policy manager with the Surfrider Foundation, said she’s skeptical many would heed the Coastal Commission guidance warning of possibly 10 feet of sea-level rise.

“Unfortunately the long-term projections and reality of sea-level rise don’t coincide well with the political cycle, so it’s very hard to get elected officials and appointed authorities to take action,” Savage said.

Sea level is long-term, while mayors and councils are elected every few years, she said.

“Very few elected officials are going to want to be the ones to tell property owners your home is not as valuable as you think it is ... because the ocean is going to wash it away, Savage said.“The political will to make hard decisions is not necessarily there.”

Reprinted from Climatewire with permission from E&E News. E&E provides daily coverage of essential energy and environmental news at