“Heat is like a death sentence.” The line, spoken by a Kuwait-based meteorologist in Jacqueline Zünd ’s “Heat,” anchors a film that examines global warming not through explanation but through what the Swiss filmmaker describes as “a sensory experience.” Premiering in the main competition at Visions du Réel , Switzerland’s leading documentary film festival, “Heat” immerses the viewer in environments where extreme temperatures are entirely reshaping the way people live and work, exposing stark