Rising sea, rising threat: What Puget Sound risks

Rising oceans over the next century can be expected to swamp half of existing Puget Sound estuary beaches, swallow tideflats and alter the spawning habitat for herring, surf smelt and other fish, and could also wreak havoc with the Sound's food web, according to a new report by the National Wildlife Federation.

Using sea-level-rise scenarios projected by an international climate-change panel that met earlier this year, the environmental group predicts that thousands of acres of what are now freshwater marshes could become salt marshes — while other marshland may simply disappear.

The group says such changes could end up affecting everything from harbor seals and seabirds to wild shellfish such as butter clams and Olympia oysters.

The report reinforces findings scientists for the state and the University of Washington issued two years ago, which determined that climate change could affect Puget Sound dramatically over time.

So the latest report was greeted Tuesday as another important reminder that climate change threatens to upset the Sound's delicate ecosystem in unpredictable ways.

"It's not like one day we have a beautifully restored salt marsh and the next day it's inundated," said Kathy Fletcher, executive director of People for Puget Sound, an environmental group. "It's gradual."

The sea-level estimates are based on the report by the Intergovernmental Panel on Climate Change, which has predicted that increasing global temperatures will cause oceans to rise about 2 feet by 2100.

Puget Sound scientists say geologic forces cause some land around Puget Sound to sink while other rises. So the impact of higher seas would vary dramatically from Cape Flattery to Olympia.

But the National Wildlife report predicts that a 2-foot rise or more in oceans could drown Dungeness Spit on the Strait of Juan de Fuca and destroy half of the current beaches in Seattle's Elliott Bay and the Duwamish Estuary. And it could eliminate nearly a quarter of swampland outside Bellingham.

Nearly a third of the Sound's shorelines already are corralled by dikes or seawalls, which may protect dry land from erosion and flooding. But those barriers can compound the ecological impacts of climate change because they already starve the shoreline of the sand and vegetation that incubate many of the most important food sources in the Sound.

Other scientists said the report's conclusions about tides and the future landscape of the Puget Sound area generally seem to mesh with their own research.

But they said gauging how life in the Sound will respond to sea-level changes is much trickier.

For example, salmon can adapt to new habitats and hiding places, and many waterfowl species have multiple species of prey. Shellfish larvae can travel great distances to change habitats.

"What we don't know is how adaptable each of these species are," said Mary Ruckelshaus, a federal research biologist for NOAA Fisheries, who reviewed the National Wildlife Federation report.

"There are probably some that aren't as vulnerable as we assume, and others that may be more so."

Still, climate change means much more than rising seas. Warmer water and reduced freshwater flows into the Sound, caused by a dwindling snowpack that melts more quickly, could compound problems even for the adaptable species.

Warmer temperatures can stress salmon, and changes to river flows alter water salinity and density, which can affect how and when microscopic plants bloom to feed the tiny sea creatures that ultimately nourish most life in the Sound.

And those are the climate impacts scientists can't yet predict with much clarity.

"The biggest concern in terms of a healthy ecosystem is really the rate of change," said Jan Newton, a UW oceanographer.

"What we all agree is bad is if we have an ecosystem that isn't supported — that the food isn't there when the hungry mouths are."

Craig Welch: 206-464-2093 or cwelch@seattletimes.com