California is Preparing for Sea-Level Extremes
Sea-level rise is a dynamic phenomenon. Historical experience indicates that sea level rise occurs in spurts. In the next several decades, California’s greatest coastal impacts are likely to be caused when an El Niño event, large storms, and high tides coming together.
A background of rising sea levels caused by global warming will exacerbate these natural effects according to Dan Cayan. He studies the extreme events that can dramatically impact coastlines.
When we get large storms that coincide with high tides, that’s when there’s the potential for the most damage.
Tide gauge and coastal wave observations are really critical in understanding what’s happening locally. The last 15 years observations have advanced a lot:
- The ocean science community can provide a view of the whole Pacific Ocean with a much better fidelity. Part of this is because of floats and gliders that have been developed by at Scripps.
- Remote sensing now provides estimates of important components such as global sea level so we have a much better ongoing description of ocean conditions.
- Atmospheric water vapor from satellites is an important ingredient in forecasting precipitation from “atmospheric river” storms, the major flood producers along the West Coast.
A whole-Pacific perspective
Decision-makers can rely on state of the art informations. Observations and models indicate that global sea levels will continue to rise in the future, probably at an increasingly high rate.
However, there is considerable uncertainty because some of the key processes are not well observed, not completely understood, and not completely captured in existing models. Sea-level rise in the next 100 years is quite likely to reach three feet above present-day levels, but it’s possible it might only reach 1.5 feet and it’s also possible it could rise to five feet. So there is an envelope of potential sea-level rise that decision-makers need to understand and plan for, weighing options of risk and expense to mitigate that risk.
A confusing aspect is that over the last several years, since our large El Niño in 1998, the West Coast has experienced essentially zero sea-level rise.
On the other hand, in the western part of the Pacific basin, sea levels have risen dramatically, at rates as high as three times the global average (as high as four inches per decade). Cayan thinks that this Pacific basin imbalance is driven by winds and ocean currents, and that eventually, within the next few years to decades, the Pacific circulation will revert to a different pattern and sea-level rise along the West Coast is going to resume. But when and how fast this happens is not clear. This underscores the need for a whole-Pacific perspective, the importance of both regional and global observations, and improved modeling.
So decision-makers will need to plan for change and also prepare for extreme events. Because the existing knowledge about sea-level rise varies quite a lot across coastal professionals, agency officials, and the general public, Cayan thinks a consortium of experts is needed to provide information in multiple ways on different levels of detail, from more basic to more expert.
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