Driver: Climate Change in the Salish Sea Ecosystem

[Editor's note: Updated information related to this chapter is available in the 2015 report State of Knowledge: Climate Change in Puget Sound.]

We all experience the weather with its day to day changes, and we are all familiar with the regular seasonal changes in climate where our weather transitions between spring, summer, winter and fall. Human caused climate change refers to sustained trends in our weather and climate patterns. Some shorter-term climate variation is normal from cycles of the Pacific Decadal Oscillation and El Niño-Southern Oscillation; however, natural variability alone cannot explain the rapid increase in global temperatures in the last 50 years (IPCC 2007). Although these natural cycles complicate determining the full extent and cause of increased temperatures, especially for regions like Puget Sound, most evidence confirms that at least some of the rise in global temperature is attributable to the buildup of greenhouse gases (Hegerl et al. 2006). The average net effect of global human activities (specifically increased greenhouse gas and aerosol concentrations from deforestation and burning fossil fuels) since 1750 has been one of warming, with a radiative forcing of +1.6 [+0.6 to +2.4] W/m2 (IPCC 2007). In comparison, changes in natural solar irradiance since 1750 are estimated to have caused a relatively small radiative forcing of +0.12 [+0.06 to +0.30] W/m2 (IPCC 2007). This range of natural and human factors driving the warming or cooling influences on global climate plays an essential role in shaping ecosystems.

A conceptual model such as Driver-Pressure-State-Impacts-Response (DPSIR) can provide context for the climate change threat (Figure 1). In the following sections, we use DPSIR terminology to help evaluate climate change related pressures to the ecosystem in terms of the classes of processes that often affect the structure (state) and function (impact) of the ecosystem. The strategies to mitigate and adapt to climate change are discussed in more detail in Chapter 4.


Figure 1. Driver-Pressure-State-Impacts-Response conceptual model for Climate Change.

The pressures that climate change exerts on the Salish Sea ecosystem fall into six general classes of processes that affect its structure and functioning: (1) water cycle changes; (2) weather/temperature change, (3) ocean thermal expansion/melting of land ice;(4) large and local scale atmospheric forcing; (5) ocean acidification; and (6) ultraviolet irradiance. Each in turn contributes to changes in ecosystem states. Note, however, that more than one pressure can contribute to a given state change; similarly, many system-level impacts are driven by multiple state changes. These various relationships are reviewed and described in greater detail below.

Although not explicitly addressed in this iteration of the Puget Sound Science Update, the impacts of climate change on the citizens of the Salish Sea ecosystem are important to consider in addition to impacts on the ecosystem. A changing climate will affect many facets, including impacts to infrastructure and human health and wellbeing. These impacts should be included in future updates.

1. Pressure: Water Cycle Changes

Hydrology in the Salish Sea ecosystem is governed by three watershed regimes: (1) high elevation is snowmelt dominant, (2) mid-elevation is transient with a rain/snow mix, and (3) low-elevation is rain dominant. Transient watersheds are most prevalent (Climate Impacts Group 2009) and will be the first to show a quantifiable response to changing climate as it trends towards to a rain dominant regime associated with increased temperature.

State: Altered Hydrology

Timing of peak streamflow varies seasonally between the three watershed regimes (Climate Impacts Group 2009). Snowmelt dominant streamflow peaks when temperatures begin to rise and melt the snowpack during May-July. Rain dominant streamflow peaks when precipitation peaks, typically during November-January. Transient streamflow is unique in that it peaks twice; once during November-January coinciding with peak precipitation and again during May-July coinciding with the snowpack melting.


The watersheds with streamflow based mostly or partially on snowmelt are predicted to have the greatest hydrological shifts associated with climate change. Snowmelt plays an integral role in the seasonal timing of streamflow and thus affects the region’s water supply. Impacts to the water cycle are likely to include earlier peak stream flows, decreasing runoff in spring/summer, and increasing runoff in autumn/winter.

In watersheds with snowpack, especially the transient watersheds, winter and spring warming are likely to cause a cascade of events that lead to more winter precipitation falling as rain and less falling as snow. Said another way, a warming climate will reduce the snow-to-precipitation ratio, resulting in reduced snowpack at the end of winter which in turn further increases the absorption of solar radiation by the land surface, triggering the snow albedo feedback to increase the rate of melting (Mote et al 2008a). This chain of events was responsible for the advanced timing of streamflow documented over the period from 1948-2000 throughout most of western North America (Stewart et al. 2005; Hidalgo 2009).

From 1980 through 2000, streamflow timing tended to come one to four weeks earlier than it did in the cooler period of the 1950’s through the mid-1970’s, with trends being strongest for mid-elevation transient zones; the trend toward earlier timing of streamflow in snowfed rivers over the 1948-2000 period is significant (p = 0.05) (Hidalgo 2009).

This advance in streamflow timing of basins with snowpack was shown with three related measures:

  • The center timing of streamflow, which is the average day by which time half of the annual streamflow has passed, occurred earlier in the spring. The early shift was present throughout western North America, including the Salish Sea region, for the period of 1948–2002 (Stewart et al 2005). For the Puget Sound Basin specifically, it is projected that center timing will occur between 1-7 weeks earlier during the 2020’s than it did on average from 1917-2006, depending on the watershed and climate change scenario considered (Climate Impacts Group 2009).
  • An advance of timing in the snowmelt onset, with mid-elevations having the largest advance due to being more sensitive to early temperature changes than high-elevations. Overall, from 1948-2002, the linear trend in spring pulse onset was 10-30 days earlier for snowfed rivers in western North America (Stewart et al 2005).
  • Decreased spring and early summer fractions onf the annual flow and increasing fractions of annual flow occurring earlier in the water year (Stewart et al 2005). In the Puget Sound Basin, flows for 2006 conditions were higher in late winter and early spring, and lower in late spring and summer compared to 1915 levels, which reflects the generally warmer winter temperatures for 2006 (Cuo et al 2009). The trend of winter peaks becoming higher and summer peaks becoming lower is projected to continue throughout the 21st century as a consequence of regional warming trends (Climate Impacts Group 2009). Transient watersheds in particular will see the largest shift in interseasonal distribution of streamflow. As snowpack decreases, streamflow is projected to shift from having a doublepeak, to only a single peak in mid-winter, associated with the loss of snowmelt and increasingly rain-dominant behavior.

In contrast to snowmelt dominated basins, rain dominant watersheds are relatively unaffected by climate change (Stewart et al 2005). The center timing of low elevation rain-dominant watershed basins trended in the opposite direction of high-elevation basins over the 1948-2002 period. Streamflow center timing of rain-dominant streams trended to 5-25 days later over the 1948-2002 period (Stewart et al 2005). This suggests that the trends seen in high-elevation basins are most likely attributable to temperature changes, rather than precipitation (Adam et al 2009; Climate Impacts Group 2009). In addition, mean annual streamflow has remained constant over the past 50 years despite seasonal shifts (Cuo et al 2009; Stewart et al 2005).

2. Pressure: Weather/Temperature Shifts

In the Pacific Northwest, regional climate models generate shifts in snow cover, cloud-cover, and circulation patterns associated with interactions between large-scale climate change and the regional topography and land–water contrasts (Salathe et al 2008). Changes in weather conditions alter the state of temperature and precipitation trends over the region. A majority of impacts to the system within the Salish Sea ecosystem are a result of interactions between increased temperature and precipitation pattern shift.

State: Increased Temperature

According to the IPCC Fourth Assessment Report (2007), globally the earth’s climate rose 0.7°C over the last century. Over this same time period, the temperature trend in the Puget Sound basin slightly exceeded the global average, generally registering a 0.8°C increase (Mote 2003). This rise in temperature is not expected to level off anytime soon, in fact the rate of change is predicted to increase over the coming century, although natural climate variations will continue to cause substantial variability between years and decades. Climate change scenarios summarized by the Climate Impacts Group show a multi-model average temperature rise in the Pacific Northwest of 1.1°C (range of projections from all models: +0.6°C to +1.8°C) by the 2020s; 1.8°C (range: +0.8°C to +2.9°C) by the 2040s; and 2.9°C (range: +1.6°C to +5.4°C) by the 2080s compared to 1970-1999 temperatures. These scenarios have warming throughout all seasons with the largest increase found in the summer months (Climate Impacts Group 2009).

State: Precipitation Pattern Shifts

Throughout North America, precipitation on average has increased over the last century (Field et al 2007) with precipitation trends in the Pacific Northwest exceeding the global average trends by 13%- 38% (Mote 2003). Southern British Columbia also had an increase in precipitation between 5-35% over the 20th century (Zhang et al 2000). Agreement among models on estimations of future amounts of precipitation in the Pacific Northwest is lacking. When results among these models are averaged, the overall projected changes in our region are modest, with a 1.3% precipitation increase; range of projections from all models: (-9 to +12%) by the 2020s; +2.3% (range: -11 to +12%) by the 2040s; and +3.8% (range: -10 to +20%) by the 2080s compared to 1970-1999 precipitation levels (Climate Impacts Group 2009).

Most models agree that there will be large seasonal changes, especially toward wetter autumns and drier summers (Climate Impacts Group 2009; Jakob & Lambert 2009). The regional models also predict increases in extreme high precipitation over the next half-century, especially in the Puget Sound area (Climate Impacts Group 2009). The seasonality, frequency and intensity of extreme events, including storms, must be considered in addition to the annual amount of precipitation since extreme events cause immediate damage to the ecosystem, versus a gradual shift in conditions over years.


Snowpack and Glaciers

The impact of rising temperature with the most far reaching effects is the erosion (or diminishing) of snowpack and glacial retreat. Regardless of how much precipitation falls in our region, ambient air temperature determines how much of that falls as snow or rain. Increased temperatures reduce the length of the snow season and increase the elevation of snowline, and thus decrease the amount of snowpack in Puget Sound.

Snow water equivalent is a common measurement of snowpack. It is the amount of water held within the snowpack and can be thought of as the depth of water that would occur if the entire snowpack melted. Stoelinga et al (2009) determined that April 1 snow water equivalent declined in the Cascade Range by 23% (95% CI: ±28%) from 1930-2007. During that same time period, the Washington State portion of the Cascade Range may have had a slightly higher percent loss, ranging from 15-35% with rising temperatures being the main source for the decline (Mote et al 2008a). While the overall result is a decline, the severity of decline depended on elevation. Low elevation sites had the largest declines and high elevations either had smaller declines or in some cases increases. Cuo et al (2009) analyzed simulated snowpack over the 1915-2006 period from individual Puget Sound basins and confirmed the influence of elevation. They found relatively moderate snow water equivalent declines (up to 23%) in the Dosewallips, Nisqually, Puyallup, and Skagit basins, which are located at relatively high elevations. However, other basins found in an intermediate elevation zone had declines greater than 30%.

Future climate scenarios reported on in several studies show an agreement that continued loss of snowpack is to be expected with rising temperatures, although the amount of decline varies among studies. Estimated changes in Washington’s snow water equivalent measurements associated with climate change depend on elevation with low elevations again expected to have the largest decrease in a warming climate. The Climate Impacts Group (2009) scenarios have low-elevation snow water equivalent declining in the range of 15-37% by 2020’s, 23-54% by 2040’s, and 39-71% by the 2080’s. For the Washington Cascade Range only, Casola (2009) estimated a smaller decline in the range of 11-21% in snow water equivalent by 2050. Future declines in snow water equivalent would likely affect water availability for both wildlife and people. For example, Puget Sound [Chapter2a.Salmonids#chinookanchor|Chinook salmon]] populations may have an increase of younger spawners and smaller proportions of stream-type fish (Beechie et al 2006) and the citizens of Puget Sound will incur declines in the municipal water supply and hydropower production (Climate Impacts Group 2009).

Along with the loss of snowpack, glaciers in the North Washington Cascade Range are also decreasing in volume and extent and are predicted to continue to shrink. Pelto (2008) found significant changes in glacier mass balance, which is the difference between accumulation and ablation and advancing/retreating terminus behavior. The annual mass balance of ten glaciers was measured over two decades (1984-2006) and were found to have a 20-40% loss of their total volume. Furthermore, all 47 glaciers that were monitored are currently undergoing a significant retreat and four of them have disappeared. This trend of mass loss has accelerated in the last 15 years and is no longer dominated by shifts in the Pacific Decadal Oscillation, indicating recent large scale climate changes are stronger than the Pacific Decadal Oscillation induced variations of earlier decades of record (Josberger et al 2007). Future losses in both snowpack and glaciers are expected to be major consequences of rising trends in regional temperatures in future decades.

Range Shifts

The loss of snowpack and glaciers at mid and high-elevations constrains and also expands opportunities for animal and plant species settlement. In a warmer climate, species will begin to shift their ranges, or become less abundant in their current range in response to rising temperatures and precipitation shifts. Using Douglas-fir as an example, the Climate Impacts Group (2009) found that by the end of the 2060’s climate will be sufficiently different from the late 20th century to alter Douglas-fir distribution in Washington State. Under the climate change scenarios they considered, roughly 32% of the area currently classified as appropriate for Douglas-fir would be outside the identified climatic envelope for this species by the 2060s. This decline of suitable habitat mostly occurs at lower elevations due to water balance deficient. Currently, at high elevations Douglas-fir is constrained by snow and low temperatures (Griesbauer and Green 2010). With climate change predicted to cause warmer temperatures, less snowfall and earlier snowmelt, Douglas-fir may have increased productivity and expand its range to higher elevations (Griesbauer and Green 2010). Thus, it is unlikely that Douglas-fir in the Pacific Northwest will exhibit substantial range contractions unless water balance deficit increases substantially (Littlell et al 2008).

More generally, Zolbrod and Peterson (1999) used a gap model to examine the effects of increased temperature (2°C) and altered precipitation on high-elevation ecosystems of the Olympic Mountains. They found in the southwest region, as tree species shift upwards in elevation with a warming climate, composition of tree species remains relatively stable. However, in the northeast region, the warmer climate results in combinations of tree species that is uncommon currently. Thus, this study suggests that species and site-specific responses at mesoscale and microscale resolutions must be characterized to quantify the variation in response of forest vegetation to climatic change.

Plants will not be the only communities to shift in response to a warming climate; wildlife too, will alter their range and abundance. Of 434 species worldwide that have been categorized as shifting in range, either measured directly at range boundaries or inferred from abundance changes within communities, 80% (P< 0.1 X 10-12) shifted in accord with climate change predictions (Parmesan & Yohe 2003).

One abundance/range shift of importance in the Salish Sea, particularly because it is an iconic group of species, is that of salmon. From the early 1800’s to the late 1900’s, the size of wild salmon runs declined by 92% in Puget Sound, 98.2% along the Washington Coast and 63.8% in British Columbia (Lackey 2003). Part of this decline may be attributable to rising stream temperatures, which cause a decrease in quality and quantity of salmon habitat.

Salmon are sensitive to thermal increases, with impairment occurring at the following stated temperature ranges for these different stages of their life history: smoltification and spawning 12-15°C, disease virulence 16°C, migration 19-23°C, and lethal threshold 24-26°C (Richter & Kolmes 2005). Future climate scenarios used to simulate future stream temperatures indicate increasing freshwater temperatures and increasing thermal stress for salmon in western Washington that are slight for the 2020s but increasingly greater later in the 21st century (Climate Impacts Group 2009). Annual maximum temperature in the 2020s at most stream stations is projected to rise less than 1°C, but by the 2080s many locations may warm by 2 to 5 °C (Climate Impacts Group 2009).

In the future, the persistence of water temperatures greater than 21°C is predicted to start earlier in the summer, and last later into the year than in previous decades (Climate Impacts Group 2009). Salmon thermal threshold level coupled with this temperature rise causes the projected loss of salmon habitat in Washington to range from 5 to 22% by 2090, depending on the climate change scenario used in the analysis (O'Neal 2002). The interaction of reduction of local riparian vegetation due to development with increased temperatures from a changing climate will likely exacerbate the loss of thermally appropriate salmon habitat, since riparian vegetation exerts a strong influence on buffering stream temperatures (Poole and Berman 2001).

Temperature increases also affect the abundance and distribution of less beneficial species in the region. Insect outbreaks can have substantial negative impacts on forest ecosystems by reducing growth and causing mortality (Kurz et al 2008). For these insects, warming is likely to cause elevation shifts and encourage northward expansion of the range of southern insects (Climate Impacts Group 2009; Parson et al 2001, Williams & Liebhold 2002). For example, low elevations will become unsuitable in a warming climate for Mountain Pine Beetle, and model simulations predict attacks will occur at increasingly higher elevations, lessening the amount of overall suitable habitat for outbreaks in western Washington (Climate Impacts Group 2009).

In another instance, the spruce budworm has been extending its range northward. Cool summer temperatures slow feeding and development of the larvae which increases its vulnerability to predators. Thus increased temperatures, coupled with drought stress (Parson et al 2001) diminish this limiting factor and allow for expanded populations. Using a simulated climate for years 2081-2100 predicts outbreaks being approximately 6 years longer with an average of 15% greater defoliation (Gray 2008).


Not only will species ranges and distributions be affected but phenology, the seasonal timing of plant and animal life cycle events, is also affected by climate change. Worldwide, 677 species were quantitatively assessed in which 27% showed no trends in phenologies, 9% showed trends towards delayed spring events, and the majority, 62% showed trends towards spring advancement (Parmesan & Yohe 2003). Of these shift changes, an overwhelming majority of species examined (87%) occurred in the direction expected from climate change (P< 0.1 X 10-12). Another meta-analysis of 1,468 species found a comparable result with 81% (90% CI: 73.4–88.6%) of the shift changes occurring in the expected direction (Root et al 2003). Trends of early life cycle changes were observed in multiple taxa including; frog breeding, first flowering, tree budburst, bird nesting and arrival of migrant birds and butterflies.

Changes in phenology are important to ecosystem function because the level of response to climate change can vary across functional groups and several trophic levels. The decoupling of phenological relationships will have important implications by altering trophic interactions and causing eventual ecosystem-level changes. Studies performed here locally already show that decoupling is occurring. In Lake Washington, due to long-term climate warming and large-scale climatic patterns like Pacific decadal oscillation (PDO) and El Niño–southern oscillation (ENSO), phytoplankton spring bloom occurred 19 days earlier in the early 2000s than it did in 1962, whereas the peak for zooplankton advanced at either slower rates or remained stable over this period (Winder & Schindler 2004).

These changes created a growing time lag between the spring phytoplankton peak and zooplankton peak, which can be especially critical to Daphnia. In addition, Daphnia are a major zooplankton prey for the juvenile sockeye salmon in Lake Washington. Hampton et al (2006) found that the gap between the arrival date of juvenile sockeye and the spring peak onset of Daphnia increased over a nine year period of study. Consequently, sockeye were forced to forage on less desirable and nutritious prey for longer periods of time. Such temperature driven phenological changes have the potential to severely impact the balance of native communities.

Placeholder: Additional phenological impacts, for example migration, wintering birds, pollinator/flowering timing.


Rising temperatures in the future are predicted to increase overall forest productivity. However, this increase will not be uniform across elevations. Lower elevations will experience declines in productivity while an increase of productivity in many higher elevation forests partially offset those declines (Nakawatase & Peterson 2006; Latta et al. 2010). For example, Douglas-fir is limited by high growing season temperatures and low growing season precipitation at low to mid elevations (495–1133m), but at high elevation (1036-1450m) current-year high temperatures lead to above-average growth (Case and Peterson 2005).

Natural Hazards

Dry, warm conditions in the seasons leading up to and including the fire season are associated with increased area burned and more numerous fires in the western region of the United States (Heyerdahl et al 2008; Littell et al 2009). In the Puget Sound/Georgia basin region, even though there is an abundant fuel load, typically the climate has been a limiting factor for fires due to high moisture levels preventing ignition and spread (Bessie and Johnson 1995). However, with climate gradually becoming hotter and drier the frequency and intensity of fire is increasing. In the western U.S., wildfire frequency from 1987-2003 increased roughly four times the average of 1970-1986 values, and the total area burned by these fires was more than six and a half times its previous level (Westerling et al 2006). This pattern is seen more specifically in the Western Cascade Range of Washington, with an average of 445 hectares (ha) burned from 1980-2006, with an expected increase to 769 ha by 2020’s, 1295 ha by 2040’s, and 3683 ha by 2080’s based on statistical fire models that explain 50-65% of the variability in area burned (Climate Impacts Group 2009). Summer temperature, which the climate modeling community has high confidence in future predictions of, is the most important factor when considering the amount of area burned (Lawler and Mathias 2007). Thus, the projected increases in wildfire should be seen as highly likely and disturbance from fire will have an increased role in impacting forest communities and associated ecosystem services.

In the Salish Sea ecosystem, warmer climate, lower precipitation, reduced snowpack and earlier snowmelt along with increased vegetative activity, enhances soil drying and causes a decrease in summer soil moisture (Climate Impacts Group 2009). With the 50th percentile being equal to mean historical values, soil moisture is projected to decrease and be in the 38th to 43rd percentile by the 2020s, 35th to 40th percentile by the 2040s, and 32nd to 35th percentile by the 2080s. Although summers are predicted to be drier, the shift towards wetter autumns will have an impact on landslide frequency. Currently the highest landslide frequency along the southwest coast of British Columbia occurs during the autumn (Jakob & Lambert 2009). Models predict that on average, a 10% increase in 4 week antecedent rainfall and a 6% increase in 24-hour precipitation can be expected by the end of the next century (Jakob & Lambert 2009). This increased level of soil saturation during autumn suggests landslides will occur even more frequently than they do currently, but it is not clear what the magnitude of this increase will be.

Placeholder: Additional natural hazards, including storms

3. Pressure: Thermal Expansion

Globally, climate change is driving a thermal expansion of the world’s oceans. When the air temperature rises, the ocean absorbs more of this heat. As the water temperature rises it also decreases in density which causes an expansion in volume; thus producing a rise in sea level. Since the circulation of the ocean slowly brings cold, deep water into contact with the increased thermal conditions at the surface, thermal expansion of the ocean will continue for roughly 1000 years after atmospheric temperature becomes stable (Mote et al 2008b).

4. Pressure: Melting of Land Ice

Global climate change is causing a decline of the world’s glaciers and ice sheets (For details regarding Cascade Range glaciers see Impacts within Weather/Temperature Pressure sections above). The rate of change in land ice can be determined by looking at its mass balance. Mass balance is measured by determining the amount of snow accumulated during winter, and then measuring the amount of snow and ice removed by melting in the summer. The mass balance is the difference between these two measurements. Globally and locally the overall trend during the 20th century has been a decrease in the mass of land ice (IPCC 2007; Pelto 2008).

State: Sea Level

Sea level rise can result from either ocean thermal expansion, melting of land ice or both. Global sea level is rising due to these two factors, although each contributes a varying amount towards the overall rise. Antonov et al (2005) and Ishii et al (2006) both found similar rates of expansion of the world’s oceans over the latter half of the 20th century. According to their research, the decades of 1955-2003 show sea level change of 0.33 ± 0.07 and 0.36 ± 0.06 mm yr–1 respectively. The last decade of this period, 1993-2003, shows sea level change of 1.2 ± 0.5 mm yr–1. However, more recent estimates of this same 1993-2003 period are slightly lower at 0.8 mm yr–1 (Domingues et al 2008). Meanwhile, glaciers and icecaps are estimated to have contributed to sea-level rise about 0.4 mm yr-1 from 1961 to 1990, increasing to 1.0 mm yr-1 from 2001 to 2004 (Church et al 2008). Thus, both thermal expansion and land ice melting seem to be increasing in rate going into the 21st century.

Projections into the 21st century by the IPCC fourth assessment report (2007) indicate that global sea level rise is expected to rise between 18 and 38 cm for their lowest emissions scenario, and between 26 and 59 cm for their highest emissions scenario. However, locally in the Puget Sound/Georgia Basin, sea level rise is determined by sea-level changes relative to the local land rather than the global average sea-level changes (Church et al 2008). The two global pressures (thermal expansion and melting of land ice) combine with local pressures (vertical land movement) to alter the state of the region’s sea level, giving a relative sea level rise.

The rate and direction of vertical land movement varies across the Salish sea ecosystem (Climate Impacts Group 2009). The Northwest Olympic Peninsula has the highest rates of tectonic uplift, roughly 2 mm/yr. While the central and southern Washington coast have lower uplift rates of less than 1 mm/yr. South Puget Sound has seen an opposite trend and has been subsiding at a rate of 2 mm/yr.

Based on the rate and direction of tectonic shift as reported by the Climate Impacts Group (2009), coupled with the average of the six central values from the six IPCC scenarios, a medium advisory level of sea level rise by location in Washington State is given (Mote et al 2008b). By midcentury (2050) sea level is advised to increase by 0 cm in the Northwest Olympic Peninsula (range: -12 to +35 cm), 12.5 cm on the central/southern coast (range: +3 to +45 cm) and 15 cm in Puget Sound basin (range: +8 to +55 cm). Projecting out 50 years farther to 2100, sea level increases 4 (range: -24 to +88 cm), 29 (range: +6 to +108 cm), and 34 cm (range: +16 to +128) in the Northwest Olympic Peninsula, central/southern coast, and Puget Sound basin respectively. However, it is stressed by Mote et al (2008b) that these calculations have not formally quantified the probabilities, sea level rise cannot be estimated accurately at specific locations, and these numbers are for advisory purposes and are not actual predictions.


Although the magnitude of future sea level rise is uncertain, the major impacts are likely to be inundation, flooding, erosion and infrastructure damage. Sea-level rise leads to coastal flooding through direct inundation providing an increase in the base for storm surges, allowing flooding of larger areas and higher erosion rates. Sea level rise is predicted to increase erosion and flooding rates on the bluffs and beaches of the Puget Sound/Georgia Basin (Climate Impacts Group 2009), although the magnitude of change will depend on location and topography.

Sea level rise will cause the landward migration of the shoreline (and associated human enterprise and settlement) as waves break higher on the beach profile. While erosion is a natural episodic process, occurring mainly during infrequent events, such as storm surge waves during high tide, sea level rise will intensify this process. In general, for the region, beach erosion rates will vary depending on geomorphic characteristics, and extent of shoreline armoring (Finlayson, 2006). The Climate Impacts Group (2009) looked specifically at Bainbridge Island beaches. They found that locations most susceptible to inundation are the uplifted beach terraces on the southern third of the island and most of the islands bays and coves. About 48% of the shoreline is armored and NOAA recommends that unnecessary armoring structures, especially those that intrude into the intertidal zone, be either modified or removed. This is due to armoring generally causing a loss of sediment and shallow water habitat, which results in deeper water and higher energy waves which weaken the protective structure (See Increased Armoring in Shoreline Development section of this Chapter for further information).

Coastal bluffs will also be affected by sea level rise. Steep bluffs rim more than 60% of the Puget Sound shoreline, rising 15 to 150 meters (Johannessen & MacLennan 2007). Bluff erosion is a natural ongoing process that provides sediments to beaches. The erosion rate of a bluff is affected by geology, waves, and weather; thus varying amongst locations. Highest erosion rates, 2-10 cm/yr, are found in the Northern Straits because of greater wave exposure and poorly consolidated sediments. Common erosion rates farther south are on the order of a few centimeters a year, or less, in most locations.

The Climate Impacts Group (2009) looked specifically at the bluff erosion rates on Whidbey, Bainbridge and the San Juan Islands. Bluff erosion rates on Whidbey occur at a rate of 1-61 cm/yr with landslides occurring frequently on the western shore. Bainbridge erosion rates vary between 5-15 cm/yr, with 20% of the shoreline classified as unstable. In contrast, the San Juan Islands with highly resistant bedrock bluffs, have relatively trivial erosion. These three sites illustrate the variety of responses expected to be seen as future sea level rises. Sites such as Whidbey and Bainbridge will be subject to increased hazards of erosion, landslides and damage, while sites like the San Juan Islands will be unlikely to be significantly affected due to the differences in substrate; sand for Whidbey and Bainbridge versus bedrock for San Juan Islands.

Placeholder: Infrastructure damage (ex: stormwater and wastewater)

Placeholder: Impacts of sea level rise on distribution of human population

5. Pressure: Large and local scale atmospheric forcing

In the Pacific Northwest, El Niño/Southern Oscillation (ENSO) and Pacific Decadal Oscillation (PDO) are both large scale patterns of hemispherical climate variability involving sea surface temperature fields that each create comparable warm and cool phases (Moore et al 2008a). However, the PDO phases can persist for 20-30 years, whereas individual ENSO events (El Niño or La Niña) typically only last for 6-18 months (Mantua and Hare 2002). The translation of ENSO and PDO related changes into observable changes in oceanographic properties can be variable and indicates local forcings are also involved. Thus, one local climate forcing parameter, surface air temperature, is found to be the primary cause of variability in the temperature of the Puget Sound, with effects of ENSO and PDO being secondary (Moore et al 2008a). In particular, winter is the season with the greatest coupling of both local and large scale forcings, with sea surface temperature having significant correlations to all scales of forcings during this season (Moore et al 2008a).

Placeholder: More detail on circulation, local weather and winds as forcings of SST.

State: Sea Surface Temperature

Globally, observations since 1961 show that while land regions have warmed faster than the oceans, the ocean has been taking up over 80% of the heat being added to the climate system and the average temperature of the global ocean has increased to depths of at least 3000m (Field et al 2007). This pattern holds true for the Pacific Northwest, where modeled sea surface temperature is 1.2°C higher, which is less than land area warming (2.0°C), but is still a significant increase relative to the inter-annual variability of the ocean (Climate Impacts Group 2009).


The coastal sea surface temperature of the Pacific Northwest helps determine the biological and physical conditions of the marine environment and estuaries. Since water temperatures higher than 13°C promote harmful algal blooms in Puget Sound, warming surface waters would likely cause earlier and longer lasting blooms. For example, from 1921-2007, the planktonic dinoflagellate Alexandrium catenella, which is associated with paralytic shellfish poisoning, had on average a 68 day window where temperatures in Sequim Bay reached the 13°C threshold for optimal growth (Moore et al 2008b). Scenarios for warmer sea surface temperature conditions in the future of 2, 4, and 6°C will expand that optimal window in Sequim Bay by 69, 127, and 191 days respectively.

Placeholder- productivity, higher trophic level impacts, phenological impacts (migration, spawning), hypoxia

6. Pressure: Ocean Acidification

Atmospheric CO2 concentration is approximately 391 parts per million by volume (Le Quéré et al 2009). This level has not been reached in at least 650,000 years, and it is projected to increase by 0.5% per year (Guinotte and Fabry 2008). In recent decades, only half of anthropogenic CO2 has remained in the atmosphere; of the remaining half, 20% has been taken up by the terrestrial biosphere and 30% by the oceans (Feely et al 2004). As the global ocean absorbs atmospheric carbon dioxide, these increasing concentrations are reducing ocean pH and carbonate ion concentrations, resulting in the oceans’ acidification (Orr et al 2005).

State: Decreased Ocean pH

Since the Industrial Revolution, the global ocean surface pH has dropped by 0.1 pH units (Guinotte and Fabry 2008). This corresponds to approximately a 30% increase in hydrogen ion concentration. According to Feely et al. (2004) by the end of the century, estimates of atmospheric and oceanic CO2 concentrations are predicted to be over 800 ppm. Additionally the level of ocean surface dissolved inorganic carbon would increase by 12%, with carbonate ion concentration decreasing by about 60%. The associated drop in pH would be roughly 0.4 units in surface waters.

In Puget Sound, acidification accounts for 24% of the pH decrease in the summer and 49% in the winter relative to preindustrial values (Feely et al 2010). Under the predicted doubling of atmospheric CO2 levels by the end of the century, the contribution of acidification on the decrease in pH would increase to 49% in the summer and 82% in the winter (Feely et al 2010).


Depth offers no protection from ocean acidification; the deepest communities, such as cold-water corals in each ocean will be the first to experience a shift from saturated to unsaturated conditions and will contract in vertical depth distribution (Doney et al 2009). By 2100, 70% of cold-water corals, key refuges and feeding grounds for commercial fish and shellfish species, will be exposed to acidified waters.

Along the west coast of Washington, the seasonal upwelling of acidified deep water reaches depths of 40-120m on the continental shelf (Feely et al 2008). While this is a natural phenomenon in the region, the oceanic uptake of anthropogenic CO2 has increased the areal extent and the potential threat of these acidified waters to many calcifying species that live along the coast. Increasing ocean acidification reduces the availability of carbonate minerals, important building blocks for marine plants and animals, and thus reduces the rate of calcification (Andersson et al 2008). Data from multiple studies compiled by Fabry et al (2008) indicate that foraminifera, molluscs, and echinoderms demonstrate reduced calcification and sometimes dissolution of CaCO3 skeletal structures when exposed to decreasing pH conditions. Ocean acidification may cause these calcareous marine species to decline, and be replaced by non-calcareous counterparts (Wootton et al 2008) altering the food web and community structure.

Placeholder- Detailed information on shifts in species dominance and community composition, altered food webs. ''' Pressure: UV Irradiance'''

UV radiation is classified as UV-A (315–400 nm), UV-B (280–315 nm), and UV–C (100–280 nm) (Kerr and Fioletov 2008). The shorter the wavelength, the more harmful it becomes to species health. If adequate amounts of ozone are present in the atmosphere, it effectively cuts off shortwave radiation at 290nm. Thus, there are important effects of changes in the intensity of solar UV-radiation resulting from stratospheric ozone depletion, particularly UV-B radiation (Solomon 2008). Since ozone strongly absorbs the radiation at UV wavelengths detrimental to most biological species, a decrease in stratospheric ozone could have a significant impact on the biosphere (Kerr and Fioletov 2008).

State: Increased UV Radiation

There are variations in incident UV radiation as a function of latitude and longitude, as well as major inter-hemispheric differences for the same latitude and season over the ocean (Ahmad et al. 2003) It is estimated that for every 1% decrease in stratospheric ozone, there is a 1% to 2% increase in UV-B transmitted to the ocean (Zhou et al 2009). In the Pacific Northwest, for UV wavelengths of 380nm and 310nm, the maximum depth limit for UV biological effectiveness based on the absorptive properties of pure ocean water plus the added absorption and scattering of dissolved and suspended materials is 30 to 40 meters (Ahmad et al. 2003).


Placeholder- reduced productivity by phytoplankton and submerged vegetation

Data Gaps and Uncertainties

A major uncertainty associated with future climate change predictions are the future emission levels of greenhouse gasses. This uncertainty can be partially evaluated by assessing multiple scenarios of various intensities of radiative forcing, for example the Climate Impacts Group (2009) used 20 such models in their predictions. However, uncertainty in how the climate system will respond is still prevalent. Zickfeld et al (2010) asked 14 leading climate scientists what contributes most to the uncertainty associated with different radiative forcing scenarios. The scientists ranked cloud radiative feedback as the factor contributing the most to uncertainties in future global mean temperature change for all scenarios. In addition, the climate scientists expect that even with new research there will only be modest reductions in uncertainty over the next 20 years (Zickfeld et al 2010). These uncertainties should be considered with developing management responses.



Adam, J. C., A. F. Hamlet, and D. P. Lettenmaier. 2009. Implications of global climate change for snowmelt hydrology in the twenty-first century. Hydrological Processes 23:962-972.

Ahmad, Z., J. R. Herman, A. P. Vasilkov, M. Tzortziou, B. G. Mitchell, and M. Kahru. 2003. Seasonal variation of UV radiation in the ocean under clear and cloudy conditions [5156-10]. PROCEEDINGS- SPIE THE INTERNATIONAL SOCIETY FOR OPTICAL ENGINEERING:63-73.

Andersson, A. J., F. T. Mackenzie, and N. R. Bates. 2008. Life on the margin: Implications of ocean acidification on Mg-calcite, high latitude and cold-water marine calcifiers. Marine ecology progress series. 373:265.

Antonov, J. I., S. Levitus, and T. P. Boyer. 2005. Thermosteric sea level rise, 1955-2003. Geophys. Res. Lett. 32:L12602.

Beechie, T., E. Buhle, M. Ruckelshaus, A. Fullerton, and L. Holsinger. 2006. Hydrologic regime and the conservation of salmon life history diversity. Biological Conservation 130:560-572.

Bessie, W. C. and E. A. Johnson. 1995. The relative importance of fuels and weather on fire behavior in subalpine forests. ECOLOGY -NEW YORK- 76:747.

Case, M. and D. Peterson. 2005. Fine-scale variability in growth climate relationships of Douglas-fir, North Cascade Range, Washington. Canadian Journal of Forest Research 35:2743-2755.

Casola, J. H., L. Cuo, B. Livneh, D. P. Lettenmaier, M. T. Stoelinga, P. W. Mote, and J. M. Wallace. 2009. Assessing the Impacts of Global Warming on Snowpack in the Washington Cascades. JOURNAL OF CLIMATE 22:2758-2772.

Church, J., N. White, T. Aarup, W. Wilson, P. Woodworth, C. Domingues, J. Hunter, and K. Lambeck. 2008. Understanding global sea levels: past, present and future. Sustainability Science 3:9-22.

Climate Impacts Group. 2009. The Washington climate change impacts assessment evaluating Washington's future in a changing climate. Climate Impacts Group, [Seattle, Wash.].

Cuo, L., D. P. Lettenmaier, M. Alberti, and J. E. Richey. 2009. Effects of a century of land cover and climate change on the hydrology of the Puget Sound basin. Hydrological Processes 23:907-933.

Domingues, C. M., J. A. Church, N. J. White, P. J. Gleckler, S. E. Wijffels, P. M. Barker, and J. R. Dunn. 2008. Improved estimates of upper-ocean warming and multi-decadal sea-level rise. 453:1090-1093.

Doney, S. C., V. J. Fabry, R. A. Feely, and J. A. Kleypas. 2009. Ocean Acidification: The Other CO2 Problem. doi:10.1146/annurev.marine.010908.163834. Annual Review of Marine Science 1:169-192.

Fabry, V. J., B. A. Seibel, R. A. Feely, and J. C. Orr. 2008. Impacts of ocean acidification on marine fauna and ecosystem processes. ICES Journal of Marine Science 65:414-432.

Feely, R. A., C. L. Sabine, K. Lee, W. Berelson, J. Kleypas, V. J. Fabry, and F. J. Millero. 2004. OCEAN SCIENCE - Impact of Anthropogenic CO2 on the CaCO3 System in the Oceans. Science. 305:362.

Feely, R. A., S. R. Alin, J. Newton, C. L. Sabine, M. Warner, A. Devol, C. Krembs, and C. Maloy. 2010. The combined effects of ocean acidification, mixing, and respiration on pH and carbonate saturation in an urbanized estuary. Estuarine, Coastal and Shelf Science 88:442-449.

Feely, R. A., C. L. Sabine, J. M. Hernandez-Ayon, D. Ianson, and B. Hales. 2008. Evidence for Upwelling of Corrosive "Acidified" Water onto the Continental Shelf. Science. 320:1490.

Field, C. B., M. L.D, M. Brklacich, D. L. Forbes, P. Kovacs, J. A. Patz, R. S.W, and M. J. Scott. 2007. North M. L. Parry and Intergovernmental Panel on Climate Change. Working Group II., editors. Climate change 2007 : impacts, adaptation and vulnerability : contribution of Working Group II to the fourth assessment report of the Intergovernmental Panel on Climate Change. Cambridge University Press, Cambridge, U.K.; New York.

Finlayson, D. P., Washington Sea Grant Program., and Puget Sound Nearshore Partnership. 2006. The geomorphology of Puget Sound beaches. Washington Sea Grant Program, University of Washington, [Seattle, Wash.].

Gray, D. 2008. The relationship between climate and outbreak characteristics of the spruce budworm in eastern Canada. Climatic Change 87:3-4.

Griesbauer, H. and S. Green. 2010. Climatic and regional patterns in Douglas-fir climate-growth relationships in British Columbia, Canada. Conference on Opportunities and Risks for Douglas-fir in a Changing Climate. Frieburg, Germany. October 18-20.

Guinotte, J. M. and V. J. Fabry. 2008. Ocean Acidification and Its Potential Effects on Marine Ecosystems. Annals of the New York Academy of Sciences 1134:320-342.

Hampton, S. E., P. Romare, and D. E. Seiler. 2006. Environmentally controlled Daphnia spring increase with implications for sockeye salmon fry in Lake Washington, USA. Journal of Plankton Research 28:399-406.

Hegerl, G. C., T. R. Karl, M. Allen, N. L. Bindoff, N. Gillett, D. Karoly, X. Zhang, and F. Zwiers. 2006. Climate Change Detection and Attribution: Beyond Mean Temperature Signals. JOURNAL OF CLIMATE 19:5058-5077.

Heyerdahl, E. K., D. McKenzie, L. D. Daniels, A. E. Hessl, J. S. Littell, N. J. Mantua, and 3rd. 2008. Climate drivers of regionally synchronous fires in the inland Northwest (1651-1900).

Hidalgo, H. G., T. Das, M. D. Dettinger, D. R. Cayan, D. W. Pierce, T. P. Barnett, G. Bala, A. Mirin, A. W. Wood, C. Bonfils, B. D. Santer, and T. Nozawa. 2009. Detection and Attribution of Streamflow Timing Changes to Climate Change in the Western United States. JOURNAL OF CLIMATE 22:3838-3855.

IPCC. 2007. Climate change 2007 : the physical science basis : contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change. In S. Solomon, D. Qin, M. Manning, Z. Chen, M. Marquis, K. B. Averyt, M. Tignor, and H. L. Miller, editors. Cambridge University Press, Cambridge; New York.

Ishii, M., M. Kimoto, K. Sakamoto, and S.-I. Iwasaki. 2006. Steric sea level changes estimated from historical ocean subsurface temperature and salinity analyses. Journal of Oceanography 62:155-170.

Jakob, M. and S. Lambert. 2009. Climate change effects on landslides along the southwest coast of British Columbia. Geomorphology 107:275-284.

Johannessen, J. and A. MacLennan. 2007. Beaches and Bluffs of Puget Sound. Report No. 2007-04, Puget Sound Nearshore Partnership, Seattle, WA.

Josberger, E. G., W. R. Bidlake, R. S. March, and B. W. Kennedy. 2007. Glacier mass-balance fluctuations in the Pacific Northwest and Alaska, USA. Annals of glaciology. 46:291-296.

Kerr, J. B. and V. E. Fioletov. 2008. Surface Ultraviolet Radiation. Atmosphere-ocean. 46:159.

Kurz, D. CC, S. G, R. GJ, N. ET, C. AL, E. T, and S. L. 2008. Mountain pine beetle and forest carbon feedback to climate change. Nature 452:987-990.

Lackey, R. T. 2003. Pacific Northwest Salmon: Forecasting Their Status in 2100. Reviews in Fisheries Science 11:35-88.

Latta, G., H. Temesgen, D. Adams, and T. Barrett. 2010. Analysis of potential impacts of climate change on forests of the United States Pacific Northwest. Forest Ecology and Management 259:720-729.

Lawler, J. and M. Mathias. 2007. Climate Change and the Future of Biodiversity in Washington. Washington Biodiversity Council.

Le Quere, C., M. R. Raupach, J. G. Canadell, G. Marland et al., C. Le Quere et al., C. Le Quere et al., M. R. Raupach, J. G. Canadell, G. Marland, and L. Bopp. 2009. Trends in the sources and sinks of carbon dioxide. NATURE GEOSCIENCE 2:831-836.

Littlell, J. S., D. McKenzie, D. L. Peterson, and A. L. Westerling. 2009. Climate and wildfire area burned in western U.S. ecoprovinces, 1916-2003. Ecological applications : a publication of the Ecological Society of America. 19:1003.

Mantua, N. and S. Hare. 2002. The Pacific Decadal Oscillation. Journal of Oceanography 58:35-44.

Moore, T. VL, M. NJ, P. MS, L. EA, B. LC, and F. LE. 2008a. Impacts of climate variability and future climate change on harmful algal blooms and human health. Environmental health : a global access science source 7.

Moore, S. K., N. J. Mantua, J. P. Kellogg, and J. A. Newton. 2008b. Local and large-scale climate forcing of. Puget Sound oceanographic properties on seasonal to interdecadal timescales. Limnology and oceanography. 53:1746.

Mote, P. W. 2003. Trends in Temperature and Precipitation in the Pacific Northwest During the Twentieth Century. Northwest science : official publication of the Northwest Scientific Association. 77:271-282.

Mote, P., A. Hamlet, and E. Salathe. 2008a. Has spring snowpack declined in the Washington Cascades? HYDROLOGY AND EARTH SYSTEM SCIENCES 12:193-206.

Mote, P. W., Washington (State). Dept. of Ecology., and University of Washington. Climate Impacts Group. 2008b. Sea level rise in the coastal waters of Washington State. Climate Impacts Group ; Dept. of Ecology, State of Washington, [Seattle]; [Olympia].

Nakawatase, J. and D. Peterson. 2006. Spatial variability in forest growth - climate relationships in the Olympic Mountains, Washington. Canadian Journal of Forest Research 36:77-91.

O'Neal, K. 2002. Effects of global warming on trout and salmon in U.S. streams. Defenders of Wildlife, Washington, 46 pp.

Orr, J., V. Fabry, O. Aumont, L. Bopp, S. Doney, R. Feely, A. Gnanadesikan, N. Gruber, A. Ishida, F. Joos, R. Key, K. Lindsay, E. Maier-Reimer, R. Matear, P. Monfray, A. Mouchet, R. Najjar, G. Plattner, K. Rodgers, C. Sabine, J. Sarmiento, R. Schlitzer, R. Slater, I. Totterdell, M. Weirig, Y. Yamanaka, and A. Yool. 2005. Anthropogenic ocean acidification over the twenty-first century and its impact on calcifying organisms. Nature 437:681-686.

Parmesan and Y. G. 2003. A globally coherent fingerprint of climate change impacts across natural systems. Nature 421:37-42.

Parson, E. A., P. W. Mote, A. Hamlet, N. Mantua, A. Snover, W. Keeton, E. Miles, D. Canning, and K. G. Ideker. 2001. Potential Consequences of Climate Variability and Change for the Pacific Northwest. Climate change impacts on the United States : the potential consequences of climate variability and change : foundation. Cambridge University Press, Cambridge; New York.

Pelto, M. S. 2008. Impact of Climate Change on North Cascade Alpine Glaciers, and Alpine Runoff. Northwest science : official publication of the Northwest Scientific Association. 82:65-75.

Poole, G. C. and C. H. Berman. 2001. An Ecological Perspective on In-Stream Temperature: Natural Heat Dynamics and Mechanisms of Human-Caused Thermal Degradation. ENVIRONMENTAL MANAGEMENT -NEW YORK- 27:787-802.                         

Richter, A. and S. Kolmes. 2005. Maximum Temperature Limits for Chinook, Coho, and Chum Salmon, and Steelhead Trout in the Pacific Northwest. Reviews in Fisheries Science 13:23-49.

Root, T. L., J. T. Price, K. R. Hall, S. H. Schneider, C. Rosenzweig, and J. A. Pounds. 2003. Fingerprints of global warming on wild animals and plants. 421:57-60.

Salathé, E. P., R. Steed, C. F. Mass, and P. H. Zahn. 2008. A High-Resolution Climate Model for the U.S. Pacific Northwest: Mesoscale Feedbacks and Local Responses to Climate Change. JOURNAL OF CLIMATE 21:5708-5726.

Solomon, K. R. 2008. Effects of ozone depletion and UV-B radiation on humans and the environment. Atmosphere-Ocean 46:185-202.

Stewart, I. T., D. R. Cayan, and M. D. Dettinger. 2005. Changes toward Earlier Streamflow Timing across Western North America. JOURNAL OF CLIMATE 18:1136-1155.

Stoelinga, M. T., M. D. Albright, and C. F. Mass. 2009. A New Look at Snowpack Trends in the Cascade Mountains. Journal of Climate- Submitted unpublished.

Westerling, H. HG, C. DR, and S. TW. 2006. Warming and earlier spring increase western U.S. forest wildfire activity. Science (New York, N.Y.) 313:940-943.

Williams, D. W. and A. M. Liebhold. 2002. Climate change and the outbreak ranges of two North American bark beetles. Agricultural & Forest Entomology 4:87-99.

Winder, M. and D. E. Schindler. 2004. Climatic effects on the phenology of lake processes. Global Change Biology 10:1844-1856.

Wootton, J. T., C. A. Pfister, and J. D. Forester. 2008. Dynamic patterns and ecological impacts of declining ocean pH in a high-resolution multi-year dataset. Proceedings of the National Academy of Sciences of the United States of America. 105:18848.

Zhang, X., L. A. Vincent, W. D. Hogg, and A. Niitsoo. 2000. Temperature and Precipitation Trends in Canada During the 20th Century. Atmosphere-ocean. 38:395.

Zhou, W., X. Tang, H. Xiao, Y. Wang, and R. Wang. 2009. Response of marine microalgae, heterotrophic bacteria and their relationship to enhanced UV-B radiation. J. Ocean Univ. China Journal of Ocean University of China 8:35-38.

Zickfeld, K., M. Granger Morgan, D. J. Frame, and K. D.W. 2010. Expert judgments about transient climate response to alternative future trajectories of radiative forcing. Proceedings of the National Academy of Sciences, in press.

Zolbrod, A. and D. Peterson. 1999. Response of high-elevation forests in the Olympic Mountains to climatic change. Canadian Journal of Forest Research 29:1966-1978.