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Thursday, February 18, 2010

Thank You for the High Tide Photos & Your Questions

By Spencer Reeder

The response to our public outreach campaign around sea level rise has been overwhelmingly positive. We received more than 100 photographs from around the region from a number of Washington State citizens. Thanks to all of you!

The regional high tides we observed in January and February provided us with a glimpse of what we are likely to see more often in the future as sea levels continue to rise as a result of global warming.

NEW! Watch the video slide show, Extreme High Tides in Washington State - February 2010

Nisqually Wildlife Refuge.  Photo by Russ McMillan Olympic Sculpture park, Seattle waterfront. Photo by Hugh Shipman.
See more February 2010 High Tide photos

Along with the photographs, we also received the following questions:
  1. Have sea levels been rising in Puget Sound?
  2. Are recent extreme high tides a fair representation of what we should expect to see with greater frequency in the future?

Let’s address each of these questions one at a time.


Question #1: Have sea levels been rising in Puget Sound?

Answer: YES.

Tide gauges located around the world operated by the National Oceanic and Atmospheric Association (NOAA) and others have documented a long-term increase in global sea levels.

One such gauge is located in Seattle. Figure 1 below shows the increase in Seattle’s sea level over the past century as measured by the NOAA tide gauge located there.
Figure 1
Other gauges located in the region, such as those in Tacoma and Port Townsend, show a similar trend. Global sea levels are rising as a result of higher global temperature (i.e., water expands as it warms) and from increased melting of land-based glaciers and large ice sheets like those on Greenland.

The rate of global sea level rise started accelerating in the 1940s. In the 1990s, the precision with which sea level could be measured was improved through the introduction of satellite based measurement techniques. (See Figures 2 and 3 below)
Figure 2
Figure 3
Analysis conducted by the University of Washington and Ecology reported estimates of future sea level rise for three regions of Washington’s coastal waters. You can read the report and find out what factors it considers: http://www.cses.washington.edu/db/pdf/moteetalslr579.pdf


Question #2: Are recent extreme high tides a fair representation of what we should expect to see with greater frequency in the future?

Answer: Research shows that sea level is rising. Higher future sea levels will produce water levels like those observed this past January and February more often.

As sea levels in the Puget Sound continue to rise, what was previously a once or twice per year extreme high tide will steadily increase in frequency over time. The UW/Ecology report provides a medium estimate for Puget Sound sea level rise by 2050 of an additional 6 inches (within an estimated range of 3 to 22 inches). Using this medium estimate, a roughly five-fold increase in the number of comparable Puget Sound very-high tide events is obtained for the year 2050. Moreover, the once or twice per year extreme high tide would increase in height and result in potentially even more inundation.

It is important to note that the specific weather conditions that exist during any particular tide event will greatly influence the actual observed water levels. For example, the presence of a low-pressure system during our recent high tides elevated water levels beyond the predicted level published in the NOAA tide tables. If winter storms coincide with similar high tides in the future we would likely experience significantly worse effects than those shown in our citizens’ photographs recently submitted to Ecology.

See Ecology's web site for more about Climate Change - Impacts, Preparation, Adaptation

See the video slide show, Extreme High Tides in Washington State - February 2010
See more February 2010 High Tide photos



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