On the 28th March switch your lights off.

"It's a little step for a man, but a big step for the mankind..."
Let's believe it will start something.

Earth Hour is an international event held on the last Saturday of March each year, which asks households and businesses to turn off their non-essential lights and electrical appliances for one hour to raise awareness towards the need to take action on climate change. Earth hour was conceived by WWF Australia and the Sydney Morning Herald in 2007, when 2.2 million residents of Sydney participated by turning off all non-essential lights. Following Sydney's lead, many other cities around the world adopted the event in 2008.

Earth Hour will next take place on Saturday, March 28, 2009 at 8:30 pm, local time.

Earth Hour 2009 is from 8:30 p.m. to 9:30 p.m. local time, 2009-03-28.
Currently, 82 countries and more than 2100 cities are 'committed to Earth Hour 2009', a huge increase from people participating in 35 countries for Earth Hour 2008.

So lets shine in this dark hour. Switch your lights off.

You can know more about this in the official website.