We're living through oil wars, wildfire smoke and extreme weather driven by a warming planet. But environmentalist Bill McKibben says one thing is finally going right: the price of clean energy has plunged, making it cheaper than ever to power the world without burning fossil fuels. He breaks down how energy from the sun became the best option on Earth — and why this narrow window of time may be our last real shot at a different future. "Energy from heaven, not from hell," he says.