Ancient rainfall records stretching 550,000 years into the past may upend scientists’ understanding of what controls the Asian summer monsoon and other aspects of the Earth’s long-term climate. Milankovitch theory says solar heating of the northernmost part of the globe drives the world’s climate swings between ice ages and warmer periods. The new work turns Milankovitch in its head by suggesting climate is driven by differential heating of the Earth’s tropical and subtropical regions.