Over the past century, mean sea level has risen nearly eight inches at the Golden Gate in San Francisco according to NOAA oceanographers, and under a medium-to-medium-high greenhouse-gas emissions scenario, mean sea level is projected to rise from 1.0 to 1.4 meters (or 4-5 feet) by the year 2100.
The Pacific Institute report, The Impacts of Sea-Level Rise on the California Coast, concludes that sea-level rise will inevitably change the character of the California coast, and that adaptation strategies must be evaluated, tested, and implemented if the risks identified in the report are to be reduced or avoided.
“California is jumping ahead in both assessing the consequences of climate change and in trying to reduce the emission of greenhouse gases,” said Peter Gleick, president of the Pacific Institute and co-author of the report. “This advance knowledge will permit smart, thoughtful, and early efforts to reduce the possible impacts of sea-level rise associated with climate change.”
The report concludes that given today’s population, a 1.4 meter sea-level rise will put 480,000 people at risk of a 100-year flood event – the standard flood used for coastal planning – if no adaptation actions are taken. A wide range of critical infrastructure and nearly $100 billion (in year 2000 dollars) worth of existing property, measured as the current replacement value of buildings and contents, are also at risk. An overwhelming two-thirds of that property is concentrated on San Francisco Bay. Populations and critical infrastructure at risk are shown in detailed maps prepared by the Pacific Institute (and available at http://pacinst.org/reports/sea_level_rise/maps/).
“People who are already in the coastal flood plain are going to see an increased risk in coming decades, and a number of communities, industries, and vital infrastructure will be exposed to new risks,” said Matthew Heberger, research associate of the Pacific Institute and co-author of the report.
Vulnerability to sea-level rise will be heightened among Californians who do not have a vehicle, do not speak English, or who live near hazardous waste facilities. Low-income households and communities of color are over-represented in these more vulnerable groups.
“We saw it with Hurricane Katrina,” said Eli Moore, research associate for the Pacific Institute’s Community Strategies for Sustainability and Justice Program and co-author of the report. “Pre-existing social and environmental inequities make some communities less able to afford emergency preparedness materials, buy insurance policies, and evacuate to escape a disaster’s harm.”
There are large sections of the Pacific coast not vulnerable to flooding, but highly susceptible to erosion. “Erosion is a natural process, but in areas where the coast erodes easily, higher sea levels are likely to accelerate shoreline erosion due to increased wave attack,” said Dr. David Revell, senior associate at Philip Williams & Associates, Ltd. (PWA).
A team of PWA scientists and engineers evaluated erosion risk from Santa Barbara north for the report, determining in one scenario that 41 square miles of California coast may be lost to erosion by 2100, threatening the homes of 14,000 people. Significant transportation-related infrastructure and property are also at risk from erosion.
“Coastal erosion is a serious problem for California due to the inherent conflict between a migrating shore and fixed property and infrastructure. Caught in the middle are our natural shores, including beaches, wetlands, and parks, where significant ecologic and recreational resources are at great risk,” said Bob Battalio, principal of PWA.
Planning smart adaptation strategies now, as part of every coastal planning process, is vital to addressing these risks. “The results of this study give a snapshot of what we face along the coast if no actions are taken and it offers advance notice of some of the smart actions California agencies and planners can take to reduce the consequences we face,” said Pacific Institute President Peter Gleick. “California is leading the effort to offset the possible ravages of climate change and sea-level rise, but if we fail to respond, the consequences will be severe.”
Co-author Eli Moore pointed out that decisions about how to use public funds can lead to inequitable distribution of costs and benefits, whether they are based on economics (protect the most valuable assets) or utility (protect the largest number of people). “With potential for a disproportionate impact on low-income households in 13 of the 20 California coastal counties, it is important for policy makers planning responses to sea-level rise to understand and address environmental justice concerns carefully and proactively,” he said.
Decisions about the types and level of protection to implement reflect the perception of the value of the threatened property, the cost of alternative measures, and political and societal factors. Coastal armoring is one potential adaptation strategy. Approximately 1,100 miles of new or modified coastal protection structures – such as dikes and dunes, seawalls, and bulkheads – are needed on the Pacific Coast and San Francisco Bay to protect against coastal flooding from a 1.4 m sea-level rise. The cost of building new or upgrading existing structures is estimated to be at least $14 billion (in year 2000 dollars), with an additional $1.4 billion per year in maintenance costs.
Nearly 20% of that investment would be needed in Los Angeles County alone, with significant investments required in Orange and San Diego counties, as well. Armoring the coast, however, comes with other costs. Building a bulkhead or piling rocks at the base of a cliff to prevent erosion can lead to the loss of the beach or wetland areas next to it – and the recreation and wildlife habitat they provide.
As an alternative to costly engineering projects to protect the coast, a range of “non-structural” responses are also possible. These allow natural processes to work, and include a retreat from the most at-risk areas, or deciding not to rebuild flood-damaged properties. Even if greenhouse gas emissions are cut to zero today, a certain amount of sea-level rise is inevitable; climate change impacts must be taken into account in the design and building of infrastructure near the coast. The Pacific Institute notes that one of the most effective responses is to limit or require flood-proof development in regions likely to be threatened in the future, a choice that requires a change in current coastal development policies and planning approaches.
The impacts of flooding are highly site-specific; regional analyses are critical for guiding land-use decisions and evaluating adaptive strategies. Determining the types of resources threatened by sea-level rise is a crucial step toward choosing an appropriate level of response and method of protection.
“Communities must identify which coastal values they want to protect, such as recreation, wildlife habitat, tourism, shipping, and economic development,” said Heather Cooley, senior research associate at the Pacific Institute and co-author of the report. “If policy makers are proactive about reducing coastal risks in coming decades, the levels of risk could be substantially reduced; the ultimate goal of the research California has been conducting on climate impacts is to be as prepared as possible and to reduce the risks we face.”
Based in Oakland, California, the Pacific Institute is a nonpartisan research institute that works to create a healthier planet and sustainable communities. Through interdisciplinary research and partnering with stakeholders, the Institute produces solutions that advance environmental protection, economic development, and social equity – in California, nationally, and internationally. www.pacinst.org.