Rising Seas in California - An Update on Sea-Level Rise Science

This report is a synthesis of the current state of the science on sea-level rise and updated projections for California - produced by a Working Group of the California Ocean Protection Council (OPC) Science Advisory Team, supported and convened by the California Ocean Science Trust. It is intended to provide the scientific foundation for updating California’s statewide sea-level rise policy guidance - the State of California Sea-Level Rise Guidance Document, initially adopted in 2010 and updated in 2013. The next update to this statewide guidance is scheduled for adoption by the OPC in January 2018, and will reflect recent advances in science around ice loss science and sea-level rise, as described in this report. Rising Seas in California provides the scientific foundation for the update, while also intended to be used with policy recommendations to support coastal hazard resiliency planning, permitting and adaptation at state and local scales.

According to the report, California has the nation’s largest ocean economy, valued at over $44 billion/ year, with the great majority of it based on coastal recreation and tourism, as well as ports and shipping. Most of the facilities and infrastructure that support this ocean economy, as well as the State’s many miles of public beaches, are within a few feet of present high tide and are at accelerating risk of sea-level rise, and related storm surge and inundation. 

In the past five years (since the existing State guidance document was developed), new models and observations have shown that the magnitudes of estimated sea-level rise have grown, especially at the upper, low probability “tail” of ranges that have been estimated. Using the methodology of Kopp et al. (2014)1 , the researchers provide projections of sea-level rise that are based on the data from tide gauges in Crescent City, San Francisco and La Jolla. It is possible that these projections underestimate the probability of extreme Antarctic ice loss which, given recent observations and model results, are said not to be ignored. In turn, the analysis and report have also included an extreme sea-level rise scenario, here called the H++ scenario. This is an unknown probability, high consequence scenario such as would occur if high rates of Antarctic ice loss were to develop in the last half of this century.

The understanding of the dynamics of ice loss has advanced significantly. The strongest driver of this shift toward higher distributions of future sea levels is the possibility of high rates of ice loss from the West Antarctic Ice Sheet under scenarios of continued increases in greenhouse gas emissions2.

Apparently, the change in the Earth’s gravitational field and rotation that would result from the loss of ice from West Antarctica would create a higher sea-level rise along the coast of California than the overall global average. For every foot of global sea-level rise caused by the loss of ice on West Antarctica, sea-level will rise approximately 1.25 feet along the California coast, not including the additional local factors. 

The report concludes with a call for imperative and immediate action. These data, along with numerous studies on the cost of inaction, suggest that uncertainty about the exact amount of future sea-level rise should not be a deterrent to taking action now. Adaptation and hazard mitigation decisions and investments in the near-term can prevent much greater losses (many times the initial cost) than would incur if such action were not taken.


Publication Date: April 2017

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  • Assessment
  • Climate science

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