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California Overhauls Its Sea Level Rise Plan as Climate Change Reshapes Coastal Life

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A man wearing a white bike helmet, yellow jacket and black pants rides through several inches of water on a submerged bike trail. Hills and clouds are in the foreground.
An aerial picture taken Jan. 3, 2022, shows a man riding a bike along a flooded Sausalito/Mill Valley bike path during a king tide in Mill Valley. King tides occur when the Earth, moon and sun align in orbit to produce unusually high water levels and can cause local tidal flooding. Over time, sea level rise is raising the height of tidal systems. (Josh Edelson/AFP via Getty Images)

Sea level rise lapping over and pushing up groundwater under the California shoreline is the next climate threat in a state already thrashed around by wildfire, drought and deluge.

State and federal scientists are preparing a comprehensive assessment of the threat that rising seas pose to California, updating a highly scientific and complicated document from 2018 (PDF) with the latest science in user-friendly guidance for local leaders.

The new sea level rise plan will incorporate federal climate models from last year and attempts to compel cities and counties to take ownership of the issue, coordinate and move rapidly to prepare for rising tides at the local level.

Currently, state and local agencies use a scattershot range of sea level rise scenarios that forecast 1 foot to more than 1 meter — more than 3 feet — of inundation. The state’s goal with this update is to shore up that messy field, said Dominique Koné, senior science officer with the California Ocean Science Trust.


“We want to ensure that if [local agencies] are going to be planning in their different ways, they at least are using the same numbers going forward and we want those decisions to be based on credible information,” he said.

The draft report, set to publish this summer, will enshrine into California planning for the first time the expectation of roughly 1 foot of sea level rise by 2050, regardless of future emissions reductions.

Ben Hamlington, research scientist in the Sea Level and Ice group at NASA’s Jet Propulsion Laboratory in Southern California, said the state providing this level of certainty should give planners an actionable number to adapt for in the near term.

“All the scenarios point us in that direction,” he said, adding that a foot of sea level rise “is as much as we’ve seen over the past 100 years.”

But, much more is possible: Sea level rise of a meter or more is “certainly on the table,” Hamlington said. “It’s just a matter of when that will potentially happen.”

The report will feature as many as five climate scenarios. Researchers said they would almost surely push the worst-case scenarios, 3 to 10 feet of sea level rise, later in this century and even into the next one, a recognition that there is uncertainty as to how fast the world cuts emissions.

Mobile homes lined up right on the shoreline, so close that the shadow of the cliff is on the water right below the homes. Waves lapping up over tan sand.
A mobile home park in Pacifica jutting along the coast. (Jason Doiy/Getty Images)

The update aims to simplify how cities, counties and agencies plan for rising tides by providing clear information about how to prepare for a far wetter future because of human-caused climate change. It will also include other factors like flood hazards from storms, earthquakes, erosion and groundwater rise, said Patrick Barnard, research scientist with the U.S. Geological Survey.

“There’s a perception that we’re relatively less at risk than other parts of the country, but we’ve massively built up these extremely low-lying areas,” he said. “We basically put ourselves in harm’s way.”

The state plans to advise cities, counties and developers to examine each project and location’s sea level rise risk. At places with more exposure and vulnerable communities, or with major infrastructure projects like highways, hospitals and bridges, developers will be asked to bolster sea level rise protections for more intense climate scenarios, said Laura Engeman, coastal resilience specialist with the Scripps Institution of Oceanography.

“We are in a new future, and everything we do has to be reevaluated consistently,” she said. “The techniques we have used in the past, we don’t quite know how they will perform in the future.”

Much of the Bay Area’s low-lying areas built on fill are sinking faster than other areas of California. That means those places may have more effects from sea level rise than others.

She advocates for a shift in mindset in how regions prepare for rising tides. Instead of each city or county preparing independently, Engeman argues it’s imperative to tackle sea level rise with a watershed approach where communities adapt together.

An island lined with tan apartments bordered by green grass. Water in the middleg ground and the skyline of San Francisco in the background.
Sea levels along coastlines in the US will rise up to 1 foot by the year 2050, according to the National Oceanic and Atmospheric Administration (NOAA). (Jason Doiy/Getty Images)

Spurring regional collaboration to prepare for sea level rise

In an early April meeting, the San Francisco Bay Conservation and Development Commission, or BCDC, previewed a report to come out later this year on the cost of preparing for rising tides. The big finding? BCDC staff tallied all 192 existing and future seawalls, levees, marshes and other adaptation projects along the 400 miles of the bay shoreline and found it will cost an estimated $110 billion by 2050.

The region has earmarked just $5.5 billion for the effort, much less than what is needed to adapt the waterline for rising tides.

More than half of the cost comes from three counties: San Mateo, Marin and Alameda.

The plan also does not consider the cost of adjusting building codes or strategies like managed retreat — moving people and businesses away from flood zones — which would greatly affect the price of adaptation.

Raised roads cross each other. Water submerges roads under the raised cement byways. A bay and dark green hills are in the background.
An aerial picture taken Jan. 3, 2022, shows an intersection completely flooded with ocean water during a king tide in Mill Valley. (Josh Edelson/AFP via Getty Images)

But if leaders fail to act, the bill could actually be much higher at around $230 billion, said Zachary Wasserman, BCDC commission chair.

“Would you, if you could, spend $110 billion to avoid $230 billion?” he asked. “I think the answer is yes. The challenge, of course, is where [the money] comes from.”

BCDC’s cost estimate is based on 4.9 feet of sea level rise and storm surge by 2050, which is much higher than the state panel of scientists said they would likely recommend as a middle-of-the-road adaptation planning parameter.

“We haven’t had major events like hurricanes that make sea level rise a visible thing in people’s minds,” said Dana Brechwald, assistant planning director for climate adaptation for BCDC. “So we don’t have that sense that it has to happen tomorrow. But we need to have all this in place long before 2050 sea level rise occurs.”

This month, San Mateo County — the county with arguably the most risk from rising seas statewide — proposed a 100-foot buffer zone between future developments and the bay. The voluntary guidance asks developers to build construction along the county’s 53 miles of waterfront above today’s high tide by around 10 feet.

“I’d love to be proven wrong and for somebody to say that OneShoreline protected us too much,” said Len Materman, CEO of OneShoreline, San Mateo County’s flood and sea level rise resiliency district.

“These developments that are coming in now or in the next few years are going to lock in what our shoreline looks like,” he said.

An aerial photo looking down on they San Francisco Bay. A river cuts through white houses and green marshland. Hills and clouds are in the background.
Residential communities and the waterways of Foster City, as seen under a dramatic sky. (Joey Kotifica/Getty Images)

Preparing for 1 foot of sea level rise isn’t enough, experts say

But even with this update, some scientists on the state panel said that preparing for only 1 foot of sea level rise by mid-century would be shortsighted. They still need to be convinced the world will reduce greenhouse gas emissions enough to prevent the worst-case scenarios.

If all the ice melted in Greenland and Antarctica, there would be more than 200 feet of sea level rise globally — which would swallow much of the Bay Area and could turn San Francisco into an island, said Gary Griggs, distinguished professor of sciences at UC Santa Cruz.

He recognizes that just a couple of feet of sea level rise would cause a global disaster.

“I’m skeptical because of the uncertainties,” said Griggs. “The starting point is people should be concerned rather than going into denial.”

Other scientists want to make sure that the report doesn’t dilute the message of the impact rising tides will likely have on the most vulnerable Californians. Kristina Hill, director of the Institute of Urban and Regional Development at UC Berkeley, was added to the task force because of her connections with community groups across the state.

“Sometimes they think of this as technical work, and they don’t want to share it with environmental justice leaders until it’s done,” she said. “I’m hoping they will invite EJ leaders before it’s done.”

Hill is also pushing for a section within the update focusing on short-term impacts like groundwater rise pushed up by rising tides, which recent science shows will happen decades before water laps over the shoreline. Her research finds rising groundwater already infiltrates toxic sites around San Francisco Bay.


“If you can’t prevent the groundwater from rising, what are you going to do?” Hill said. “That’s the conversation I really want to have because it shows that conventional adaptation is not going to be enough. We really just need to start preparing for this potential of between 4 and 10 feet and see who’s ready for what.”

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