Photo by lucalocatelliphoto / A skier descends the artificial slopes of Amager Bakke, Copenhagen’s waste-to-energy power plant. Claiming to be the world’s cleanest incinerator, Amager Bakke doubles as a learning space for sustainability and circularity and an public outdoor space—a centerpiece of the Danish capital’s skyline that provides hot water and electricity to the city. Incinerators are seen as an end-of-pipe solution to get rid of our waste, which is why Amager Bakke has been designed from the ground up to one day be fueled by biomass, making it a promising solution for energy security. I had the chance to investigate incineration and other examples of energy production in my latest cover story for National Geographic magazine, called the "End of Trash," which covers circular-economy solutions. It has the potential to impact resource use, pollution, and emissions by designing waste out of the production system. Scientists claim we only have a few years to halt and reverse...