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Changes to Date: Sea level has risen. The closest tide gauge is in Seattle. According to NOAA, sea level has risen 7.8 inches over the last century. [b]
Expected Future: Additional sea level rise is expected of 4 inches (range of 1-6 inches) by 2030, 7 inches (range of 1-14 inches) by 2050 and 23 inches by 2100 (range of 6 to 55 inches), depending on future global trends in greenhouse gas emissions and glacial melt rates. [a]
Changes to Date: Ocean pH has already dropped by about 30% as the oceans absorb increasing amounts of carbon dioxide. [c]
Expected Future: Ocean acidity is projected to increase by between 38 and 109 percent by 2100 relative to 2005 levels[c]. Corrosive conditions are particularly of concern to the shellfish industry in Puget Sound, which depends on good water quality to grow oysters, clams, and mussels.
Changes to Date: Stream temperatures in the Pacific Northwest are projected to increase 1°F over 1980 averages by 2020. [c]
Expected Future: Stream temperatures in the Pacific Northwest are projected to increase by 3°F by 2080. [c] Warmer water temperatures will result in more lake closures and could be lethal to salmonids and other aquatic species.
Changes to Date: From 1913 to 1994, Mt. Rainier glaciers decreased by approximately 25 percent. Preliminary data from Mount Rainier National Park indicates that the glacier has lost another 18 percent since 2003. In all years between 2003 and 2009, there has been a net melting of the Emmons and Nisqually Glaciers between 0.5 and 2.0 meters water equivalent. [f]
Expected Future: Current trends indicate that Mt. Rainer’s glaciers—and others contributing to summertime stream flows and sedimentation in Puget Sound watersheds—will continue to melt as temperatures warm.
Changes to Date: Average annual temperatures for the Pacific Northwest have risen 1.3°F since 1895.[b] Pierce County has experienced an increase in forest fires during the droughts of 2015 and 2017.
Expected Future: More extreme heat is likely, although the increase may be moderated by changes in weather patterns. There is strong agreement among climate models that extreme heat events will become more frequent while extreme cold events will become less frequent. Wildfires are expected to become more common as temperatures rise and less rain falls during summer months.
Changes to Date: Landslide data not currently available.
Expected Future: landslides are expected to become more common in winter and spring [c] due to projected increases in extreme precipitation events and increasing winter precipitation, particularly in areas most prone to present-day landslides. Changes in landslide frequency and sediment transport can affect water quality, aquatic and coastal habitat, flooding, and relative sea level rise.
Changes to Date: The stream gauge on the Puyallup River near Orting has been in operation since 1932. Eight of the top ten peak floods have been recorded since 2006. [e] The timing of peak spring streamflow shifted earlier by 0-20 days in many snowmelt-influenced rivers in the Pacific Northwest between 1948 and 2002. [h]
Expected Future: Flood risk is projected to increase during the fall and winter seasons as warmer temperatures cause more precipitation to fall as rain over a larger portion of the basin. Less snowmelt will cause the lowest flows to become lower in the summer months.
Changes to Date: Historically, large volumes of sediment were removed from local rivers to increase channel capacity. However, this practice did not prevent flood losses in the valley and was ceased due to concerns about impacts to salmon habitat and natural river channel processes. From 1984 to 2009, the channel elevations of the Puyallup, White and Carbon Rivers rose by several feet in some locations. [b]
Expected Future: For rivers originating on Mount Rainier, including the Puyallup, White, and Carbon Rivers, sediment loads are expected to increase, further contributing to flood risk, as declining snowpack and glacial recession expose more unconsolidated soils to rain, flood flows, and disturbance events.
Changes to Date: Locally, an increase in extreme precipitation has been observed in Tacoma since 2010. [b] Since records started in the 1890`s in Seattle there have only been two years with at least 10 days with an inch or more of precipitation, 2015 with 14 days and now 2017 with 10 days. [g]
Expected Future: Total annual precipitation in the Pacific Northwest is not projected to change substantially, but heavy rainfall may be more frequent and intense, and summer precipitation may decrease. More rain and less snow will fall in the winter. [a]
[a] UW Climate Impacts Group: State of Knowledge: Climate Change in Puget Sound (2015)
[b] Tacoma Climate Change Resilience Study (2016)
[e] National Weather Service, Puyallup River Gage
[f] Paul Kennard et al., (2010)
[g] National Weather Service Daily Forecast