Two days after the historic People’s Climate March, world leaders are gathering in New York City today for a United Nations summit on climate change. President Obama, along with more than 100 heads of state, are expected to attend. But the leaders of several major polluters, including China, India and Canada, are skipping the talks. The summit is part of a lengthy and so far failed process leading to climate negotiations in Paris next year, when countries will seek a binding deal to limit the emissions that cause global warming. We speak to three leading environmentalists: Vandana Shiva of India, Desmond D’Sa of South Africa, and Winona LaDuke of the White Earth Reservation in northern Minnesota.