About the Puget Sound Institute

Climate change
decline 56 to 74 percent from levels 100 years earlier. The decline will reach 80 percent by the
2040s in the headwaters of the four rivers (the Tolt, Cedar, Green, and Sultan) serving the cities
of Seattle, Tacoma, and Everett—reflecting the fact that their snowpacks are already very low,
hence vulnerable. By the 2080s, April snowpack will largely disappear from all four watersheds,
leaving Puget Sound’s major rivers low and dry in summer (Elsner et al., 2010).
Impacts on salmon
These shortfalls will have wider impacts. Salmon, keystone species and traditional cultural,
subsistence, and economic mainstays along Puget Sound, will face new threats in addition to
those that have already drastically diminished their runs. Rising stream temperatures can be
deadly to fish that evolved to thrive at 12 degrees Celsius and endure no more than 18 degrees.
To the traditional “four Hs” threatening salmon (harvest, hydropower, hatcheries, and habitat
degradation), add a fifth: heat.
Earlier snowmelt, heightened streamflows, and increased flooding could also disrupt salmon’s
spawning cycles and sweep away their “redds,” the gravel beds where they deposit their eggs.
These effects will be augmented by losses in the region’s once-great conifer forests. Trees are
essential to the conditions salmon need to spawn and grow: they shade streams, create deep
pools that help to contain stormwater, and stabilize soils, preventing floods and erosion. The
salmon in turn convey fertilizing marine nutrients to the forests in the form of their own bodies,
consumed and scattered by land-based predators and scavengers.
Increased algal blooms
Warming may have profound trophic effects in Puget Sound itself. Global ocean near-surface
temperatures are projected to rise by as much as 2 degrees Celsius by century’s end—an effect
amplified in the shallow, sheltered bays of the South Sound. Already warmer waters are
nurturing earlier and larger harmful algal blooms and creating the right conditions for types of
harmful algae not previously seen in these waters. Warming and an increase of carbon dioxide
in the atmosphere, coupled with nutrient runoff and discharges from industry, farms, lawns,
and waste treatment systems, stimulate the growth of phytoplankton generally. When these and
other organisms die and sink, their decomposition consumes oxygen and releases carbon
dioxide into the water, promoting two climate-related syndromes deadly to many marine
organisms: too little oxygen in the water and water that is so acidic that it eats away the calcium
shells that protect so many of the small creatures of the ocean.
Ocean acidification
By 2100, the relative acidity of the global ocean is expected to be 50 to 100 percent above
preindustrial levels. Regional factors will compound this effect in Puget Sound. Because colder
water can absorb more carbon dioxide than warmer, much of humankind’s rapidly accelerating
atmospheric emissions of CO 2 concentrate in the deep ocean, then cycle back up some 30 to 50
years later off the Pacific Coast. Prevailing winds and currents drive these cold, CO 2-saturated,
highly acidified waters into shore, and into the Strait of Juan de Fuca and Puget Sound. There,
nutrient runoff and decomposition inject more CO 2 and acidity into the system. These inputs
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