Robert Redford is director of the Natural Resources Defense Council.

The Speech of Pope Francis in Congress will go down in history as a day when it was finally shifted the focus on climate change. The appropriate message of the pope on the need for more dialogue and less discord, respect for life in all its stages, and its appeal to protect our common home is irrepressible and impossible to ignore. Sometimes you need a friend to tell you the truth. He wanted someone from outside the United States to come to remember who we are – and who we should be. If we continue to pollute the planet with the dirty energy, the highest price you will pay our children. Polluted air is already killing hundreds of thousands of people each year. Floods, drought, fires, hurricanes: just open your eyes to see the damage caused, and all this will get worse. We can no longer pretend not to know in order to justify the fact that we do nothing. It can no longer doubt that climate change is real. This is not a threat to the future, but it happens here and now. And as Pope Francis so eloquently points out, climate change is a moral imperative that transcends politics. I feel growing in me a sense of urgency, but also of hope for the future. The clean energy revolution is taking off. Fifty-five countries around the world already derive most of their energy from renewable sources. Many villages across India and Africa are illuminated by clean energy. The Pope himself says that fossil fuels will have to be replaced ‘without delay’. But while the establishment that pollutes still singing its siren song, you need a bold leadership to seize these opportunities. Cities such as Los Angeles, Paris and London can pave the way, while Sydney, Stockholm and Bogota are already oriented to achieve 100% clean energy.