Marine scientists across the world are racing to tackle the most urgent environmental challenge facing our planet today - ocean acidification. From the icy polar seas to the world's most pristine coral reefs we track the latest scientific research. Heading the investigation is Dr Katharina Fabricius from the Australian Institute of Marine Science. She's made a game-changing discovery. Nestled amongst Papua New Guinea's stunning coral gardens is a unique reef - a window to the future of our oceans.