The Earth Day (April 22) Blu-ray release of their Oscar-winning digital space western is just the first holler. The commitment to plant a million trees around the world with the help of the Earth Day Network is the second. But the two intrepid filmmakers, who also brought the monolithic Titanic to the big screen, say the success of Avatar has brought with it a huge responsibility to keep the environmental message afloat in a sea of political bile.