The Cannes Film Festival's closing film on Saturday was a call to arms to tackle climate change featuring the scientific pioneer who spent decades in Antarctica proving the existence of global warming. "I used to be pessimistic, but I think people are changing," said Claude Lorius, the 91-year-old French scientist whose groundbreaking research on ice cores proved the link between greenhouse gases and global temperatures. His story is told in the documentary "Ice and the Sky", featuring footage from his earliest missions in the 1950s through to the present day.