Much of the globe has seen record-breaking temperatures in recent heat waves that seem increasingly routine. Dhruv Khullar, a contributor and a practicing physician, looks at the effects of extreme heat in India, where the capital, New Delhi, recorded a temperature this year of 122 degrees. “People are amazingly resilient,” he notes. “But I think we’re approaching that point where even the most resilient people, the type of lives that they have to live—because of climate change—are not going to be sustainable for very much longer.” And the climate activist Daniel Sherrell talks about his book “Warmth: Coming of Age at the End of the World” with Ngofeen Mputubwele. The book articulates Sherrell’s view that we can live now only by walking a tightrope between hope and despair.