We mark Earth Day with a special program, following efforts to combat climate change in the present and digging into why it’s taken so long to take action in the past. We begin in Chile, which has a brand new government with a serious climate agenda. Christiane discusses this with Chilean climate scientist turned environment minister Maisa Rojas. Then we welcome Dan Edge, producer of a new, three-part Frontline series, "The Power Of Big Oil," which focuses on the missed opportunities to mitigate the climate crisis. Walter Isaacson follows with an interview with Ukrainian climate activist Svitlana Romanko. And we conclude with a report on how to combat the scourge of plastic pollution.