As the climate warms, oceans expand and polar ice caps melt. This means sea level rise is a reality that land owners and local governments must prepare for. It brings with it associated risks, such as flooding and erosion which can impact everything from sewage treatment plants to roads and bridges.
A new report from Washington’s "Coastal Resilience Project" homes in on exactly how high the tides could rise in 171 different sites and communities based on the latest science.
Harriet Morgan, a research consultant with the University of Washington’s Climate Impacts Group, helped craft the study. At the Coleman ferry dock on Seattle’s waterfront, she stands near the spot where a tide gauge has been measuring water levels for more than a century.
“So this is actually one of the great ways that we’re able to see what sea level rise has been doing over the past 100 years. And we’ve actually seen that since the year 1900, sea level in Seattle has actually risen 8.6 inches,” Morgan says.
The rate at which the ocean is expanding is also increasing. According to this latest report, a good estimate is that the water will go up by about two feet everywhere by the end of this century, assuming a “business as usual” scenario for our greenhouse gas emissions.
But that so-called “absolute sea level change” doesn’t take into account what the land is doing during that time. In Seattle, the shoreline of Puget Sound is subsiding.
So, Morgan says, it’s reasonable expect to lose more than two feet here to sea level rise.
“Our central estimate is 2.3 feet by 2100 for Seattle, under a high greenhouse gas scenario,” she says.
These are complex scenarios with a wide range of inputs and factors that could shift the estimates in one direction or the other. So, the novel thing about this report, Morgan says, is that they actually provide a range of numbers for estimated sea level change in each place – along with probabilities – so that planners can decide how much risk they are willing to take on.
In Seattle, the report says there’s a likely range of sea level rise between 1.7 and 3.1 feet, by 2100. (That’s under the same business as usual, high greenhouse gas scenario.)
“And for kind of a visual reference of what that looks like, that goes from my knee to my hip – and I’m about 5-foot-8,” Morgan says.
That range is roughly the same in South Puget Sound, including Tacoma.
But in other areas of the state, where the land mass is rising, the ranges of sea level rise are less – for example, in Neah Bay. How big an effect people ultimately see will depend on how much we reduce our greenhouse gas emissions and where things are built now and into the future.
The new report is funded primarily by the National Oceanic and Atmospheric Administration (NOAA)'s Regional Coastal Resillience Grants Program. The researchers say their approach of “zooming in” and taking more factors into account is more useful than relying on data from other federal sources, such as FEMA, where flood mapping is based on historical data.
