Sustainability researcher Michael Sivak estimates that the potential demand for energy to cool Mumbai, India with air conditioning would equal a quarter of the energy used to cool the entire United States, based on the city’s large population and high temperature. As A/C comes online in more and more households and cities around the globe, how sustainable is satisfying the desire for cool air?

Kiel Moe, a professor of architecture and energy at Harvard, talks about historic efforts to keep cities and homes cool—such as importing piles of snow from the mountains—and how we might cool our homes and bodies in lower-energy ways, such as smarter use of building materials like concrete and wood.