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Climate change related information and resources from King County GreenTools program

Climate change

Human activities are the most significant factor in the striking increase in atmospheric greenhouse gases (GHGs) during the past century. Increased GHG levels are the primary cause of human-caused climate change. Critical impacts of global climate change are already occurring locally; in the Pacific Northwest, the consequences of climate change include:

Water and snow

  • Decreased water for irrigation, fish, and summertime hydropower production and increased urban demand for water, leading to increased conflicts over the resource.
  • Warmer winter temperatures and increased winter precipitation are projected to reduce the winter snowpack. This will also delay the opening of the ski season, shorten the length of the season, and increase the likelihood of rain when ski areas are open. The impacts are greater for mid-elevation ski areas (~3,000 to 4,000 feet) than for those at higher elevations.


  • Increased difficulties for migration and spawning due to increased winter floods, decreased summer streamflow, and increased water temperatures.


  • Potential increases in forest fires.
  • Overall, the Pacific Northwest is likely to see increased forest growth region-wide over the next few decades followed by decreased forest growth as temperature increases overwhelm the ability of trees to make use of higher winter precipitation and higher carbon dioxide.


  • Potential for extinction of local populations and loss of biological diversity if environmental shifts outpace species migration rates and interact negatively with population dynamics.

Coastal flooding and erosion

  • Increased coastal erosion and beach loss due to rising sea levels
  • Increased landslides due to increased winter rainfall
  • Permanent inundation, especially in south Puget Sound around Olympia
  • Increased coastal flooding due to sea level rise and increased winter streamflow from interior and coastal watersheds.


  • Many crops will grow better with higher CO2 and a longer growing season before temperatures substantially increase, provided there is sufficient water. However, some pests and weeds will be similarly advantaged. Low-value irrigated crops may have difficulty competing for less abundant water.

King county's response

King County has taken a number of actions to begin addressing the challenges presented by climate change. These actions include:

State environmental policy act

The Washington State Environmental Policy Act external link requires environmental review of development proposals that may have a significant adverse impact on the environment.

If a proposed development is subject to SEPA, the project proponent is required to complete the SEPA checklist. The checklist includes questions relating to the development's air emissions. The emissions that have traditionally been considered cover smoke, dust, and industrial and automobile emissions. The SEPA checklist is available online.

King County is the first local government in the nation to officially add greenhouse gas emissions to the environmental review of construction projects. King County's policy covers projects undergoing environmental review mandated by the SEPA and applies to the County's own developments as well as projects where the County is the lead permitting agency.

Related information

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