Latest science on sea level rise projections: In support of California policy guidance

California leads the way in both addressing climate change and protecting our coastal and ocean communities and resources,” said Jenn Eckerle, Deputy Director of the Ocean Protection Council. “Our statewide policy on sea-level rise is another example of that leadership.  We provide guidance to state agencies and local governments for incorporating sea-level rise projections into planning, permitting, investment, and other decisions, so it is critical that it is grounded in the best and latest science.”

The current State of California Sea-Level Rise Guidance Document, released in 2010 and updated in 2013, included a range of projections over various timescales, but did not estimate the likelihood that such levels would be met.   The scientific team’s new report includes information on the likelihood of specific scenarios and provides a framework for evaluating risk, adaptive capacity and consequences from rising seas.  This will allow local and state stakeholders to weigh the costs and benefits of taking action now against the potential harmful effects of inaction.

The science report will inform California’s sea-level rise guidance document, which will help cities and counties as they comply with state law that requires them to incorporate climate change into their planning efforts. The updated guidance document will also assist state agencies prepare for, and adapt to sea level rise, as directed by Governor Brown’s April 2015 Executive Order on climate change. Public input will be integrated into the final guidance document update, which is scheduled for adoption by the California Ocean Protection Council in January 2018.

The seven scientists who synthesized the latest science as a working group of the Ocean Protection Council’s Science Advisory Team, convened by the California Ocean Science Trust, are Gary Griggs, University of California, Santa Cruz; Dan Cayan, Scripps Institution of Oceanography; Claudia Tebaldi, National Center for Atmospheric Research; Helen Amanda Fricker, Scripps Institution of Oceanography; Joe Arvai, University of Michigan; Rob DeConto, University of Massachusetts; and Robert E. Kopp, Rutgers University.

Among their key findings:

• Scientific understanding of sea-level rise is advancing at a rapid pace. Projections of future sea-level rise, under high emissions scenarios, have increased substantially over the last few years, primarily due to new and improved understanding of mass loss from continental ice sheets.

• The rate of ice loss from the Greenland and Antarctic Ice Sheets is increasing. These ice sheets will soon become the primary contributor to global sea-level rise, overtaking the contributions from ocean thermal expansion and melting mountain glaciers and ice caps.

• Mountain glaciers contain enough ice to raise sea levels by only about 1.5 feet. In contrast, the Greenland and Antarctic ice sheets contain enough ice to raise global mean sea level by 24 feet and 187 feet, respectively. Although these ice sheets are not expected to melt completely, even on century or millennial timescales, the loss of even a small fraction of either of these huge ice sheets could have devastating consequences for global shorelines.

• For California, ice loss from Antarctica, and especially from West Antarctica, causes higher sea-level rise in than the global average. For every 1 foot of global sea-level rise caused by loss of ice on West Antarctic, sea-level will rise approximately 1.25 feet along the California coast. 

• After 2050, sea-level rise projections increasingly depend on the trajectory of greenhouse gas emissions. 

• While model results have revealed the potential for high rates of ice loss and extreme sea-level rise during this century if greenhouse gas emissions continue unabated, the precise magnitude and timing of when the Antarctic Ice Sheet may begin to contribute substantially to rising sea levels is uncertain.

• It is clear that sea-levels are rising. As cities, counties, and state agencies make decisions about adaptation and hazard mitigation efforts, it is increasingly important to incorporate long-range planning for sea-level rise. Consideration of high and even extreme sea levels in decisions with implications past 2050 is needed to safeguard the people and resources of coastal California.

— Read more in Rising Seas in California: An Update on Sea-Level Rise Science (California natural Resources Agency / California Ocean Science Trust / California Ocean Protection Council, April 2017)