The Space Needle joined millions of individuals, businesses and landmarks around the world by turning off its exterior lights between 8:30pm and 9:30pm Saturday.
Lights at Seattle City Hall, the Seattle Center, and the Seattle Art Museum were also turned off.
Communities were going dark for an hour as part of an initiative called Earth Hour, to raise awareness of climate change.
In more than 7,000 cities and towns across the planet, millions of residents are turned off their lights for an hour from 8:30 to 9:30 p.m. local time to show their environmental concern.
Earth Hour began in Sydney, Australia as a symbolic event to reduce greenhouse gasses and has evolved into a global movement. Organizers say if the greenhouse reduction achieved in Sydney during Earth Hour was sustained for a year, it would be equivalent to taking 48,616 cars off the road for a year.