Mark your calendar for tomorrow, March 29, when cities around the world will switch off non-critical lights at 8 p.m. for an awareness-raising Earth Hour. At present, 24 cities -- with a total population of some 30 million people -- plan to participate in the energy-saving symbolism, from Toronto to Tel Aviv, Bangkok to Brisbane, Canberra to Copenhagen, and Sydney to San Francisco. Thousands of individuals and businesses have also signed on to come to the dark side.   Individuals can sign up to participate and make a commitment to reducing energy consumption in the year ahead at EarthHour.org. During Earth Hour, the Climate Savers Computing Initiative is also encouraging individuals to "click on" computer power management features, then "click off" (power down) their computers for the remainder of the hour.  With a few mouse clicks, your computer can be set to automatically go to "sleep" when it's not in use, which can save nearly half a ton of CO2 and over $60 a year in energy costs. To learn how to turn on computer power management, visit www.climatesaverscomputing.org/tools/pwr_mgmt.html.

Also, Denver is supporting Earth Hour. Click here to see a copy of a letter from Mayor Hickenlooper.