Agence France-Presse: Major cities and world landmarks plunged into darkness Saturday as a symbolic energy-saving exercise unfolded across the globe, calling for action to avert potentially devastating climate change. The Egyptian pyramids at Giza, the Acropolis in Athens, Niagara Falls and the Eiffel Tower were set to switch off the electricity as countries worldwide prepared to join in “Earth Hour.” In London, demonstrators protesting in their thousands on poverty and environmental issues said …