What would it take to solve Earth’s grand environmental and sustainability challenges? For our first-ever special issue, Momentum magazine invited more than two dozen experts from around the world to give us their take on how we might craft solutions to some of our planet’s biggest problems. Check out M. Sanjayan’s suggestions for stemming the loss of biodiversity, Peggy Liu’s perspectives on supplying global energy needs with renewables, Alex Steffen's vision for sustainable cities and lots more.