It's going to be a lot more symbolism than substance today when nearly 3,000 cities and towns across the world turn out lights to express concern about global climate change. Major cities in Asia, the Middle East and Europe have already gone dark and it's only Saturday afternoon in the United States. "We think we are going to have 100 million people around the world sending a message that climate change is real, and we need to take action now," said World Wildlife Fund CEO Carter Roberts, according to Cable News Network (CNN). "The world is watching to see what America is going to do because if America acts on climate change, the world will follow." The participation of the United States in international agreements to address climate change is crucial because it is one of the leading producers of greenhouse gases, which are blamed for much of the problem. After helping to negotiate the Kyoto emissions reduction treaty in 1997, the U.S. famously withdrew from the agreement before it took effect in 2005. More than 650 communities in the Philippines, one of the first countries in the world to reach 8:30 p.m., participated in the Saturday's event. Lights began going out first in Sydney, Australia, birthplace of the Earth Hour idea in 2007. Hundreds of Australians lined Sydney harbor to watch the city's lights begin to go out, CNN said. Lights went out at monuments around the world, including the pyramids in Egypt, the Vatican, the Eiffel Tower and the Acropolis in Greece. But something tangible could be accomplished by the event. Organizers want to bring the global concerns to the attention of world leaders attending an international summit on climate change in Denmark later this year, according to CNN.