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Important climate change related shifts in King County’s physical environment have been observed in recent years, and are documented in this indicator. King County is tracking these changes in the local environment to help assess the severity of local climate-influenced impacts. King County is also tracking Human Health and Economic Impacts of Climate Change of Greenhouse Gas Emissions at the Community Level and the Climate Protection Response of King County Government Operations.

Increasing air and water temperatures, acidifying marine waters, increasing fall flooding, rising sea levels, decreasing snow pack, and decreasing summertime river flows are examples of changes that have been observed in King County; these trends are consistent with expected and projected local climate change impacts, and many other impacts are also occurring.

Nine key environmental indicators impacted by climate change are briefly described below:

Stream temperatures During the period 2000-2011, the moving 7-day average of the daily maximum temperatures for the majority of the 63 stream and river sites in King County exceeded the 16°C temperature standard established for the protection of salmon habitat.
Large lake temperatures The trend in annual average lake temperatures, including Lake Washington and Lake Sammamish, is toward higher average water temperatures.
Summer stream flows Trend analysis of long-term King County river discharge records (1962-2008) in nine unregulated rivers and the naturalized flow record for the Green River at Howard Hanson Dam provided strong evidence for declining trends in summer flow (July - September) and some evidence that severe storms and floods were occurring more frequently during late fall months.
Rainfall Annual precipitation increased 14% for the period 1930-1995 in the Pacific Northwest region. There is some evidence from local weather and gauging river stations that severe storms and floods are occurring more frequently. A local study indicated a general trend toward higher precipitation in November and lower precipitation during summer. In addition, results suggest increases in the magnitude, duration, frequency, and earlier timing of extreme precipitation.
Sea level rise Oceans rose approximately 8 inches from 1870-2008, an average of 0.06 inches per year. Recent years have shown an increase in the rate of change. At a station in Seattle, WA, the mean sea level trend of monthly mean sea level data(1898 to 2006) is 2.06 mm/year (equivalent to a change of 0.68 feet in 100 years).
Air Temperature In the Pacific Northwest, average annual temperatures rose 1.5°F in the last century.
Snowpack Widespread declines in springtime snowpack have occurred in much of the North American west between 1925 and 2000. Between about mid-century to 2006, decreases of about 15-35% in snow water equivalent in the Cascades Mountains were observed.
Sea surface temperatures Global sea surface temperatures increased over the 20th century at an average rate of 0.12°F per decade. Over the last 30 years, global a surface temperatures have risen at a faster rate of change of 0.21°F per decade. Records from a nearby station in Victoria, BC indicate a long-term warming trend of 1.7°F since 1921 and 1.8°F since 1950.
Ocean acidification Over the past 250 years, oceans have absorbed about 550 billion tons of CO2 emissions, or about 30% of total carbon emissions created by human activity. Globally, ocean surface water pH is estimated to have fallen about 0.1 pH units since the beginning of the industrial revolution.

See the References below for details supporting the information presented above. For more information about local climate change impacts, see the University of Washington’s Climate Impacts Group. In addition, more detailed data is presented below for two of these impacts – Stream Flows and Sea Level Rise:

Stream Flows

Between 1962 and 2008, a strong downward trend in summertime water volumes in King County rivers was observed at all 10 local unregulated river gauging stations. During this same period, there was also some evidence from these gauging stations and from eight King County weather stations that severe storms and floods were occurring more frequently during late fall months.

Frequency of trend direction and relative evidence of trends for monthly average discharge (1962-2008). Mostly strong and very strong downward trends were observed in summer flow during July, August and September (KC WLRD. 2010).

Sea level rise

Between 1898 and 2006, the mean sea level trend in Seattle, WA was a 2.06 mm/yr rise (equivalent to 0.68 feet/100years) (NOAA. 2012).

Mean sea level trend in Seattle, WA (1898-2006). A rising sevel trend of 2.06 mm/yr (0.68 feet per100 years) was observed at a station in the Seattle, WA area. (NOAA. 2012).

Other impacts on the local environment related to climate change include:

  • Increases in runoff during storm events;
  • Declines in summer runoff due to glacier loss;
  • Lowering of groundwater levels;
  • Increases in urban heat island effects;
  • Losses or increases in losses of wetland and nearshore habitat acreage;
  • Changes in the timing and duration of growing season;
  • Decreases in species abundance
  • Increases in species morbidity; and
  • Increases in biological invasions and occurrences of harmful algal blooms.