Millions are expected to turn off lights and appliances for an hour at 8:30 p.m. Saturday. This year marks the fifth annual Earth Hour organized by the fund.
The National Cathedral says it plans to participate again this year. The fund says others pledging to participate this year include the city of Baltimore, where City Hall lights will be dimmed, as well at the National Aquarium.
Four thousand cities in more than 120 countries participated last year in the event that is backed by the United Nations as well as global corporations, nonprofit groups, schools, scientists and celebrities.