In the late ninth century a disastrous harvest precipitated by drought brought famine to China, ultimately ending the three-century rule of the Tang Dynasty. Climate change may have been a cause, according to a stalagmite from northwestern China. Composed of calcium carbonate leached from dripping water, the stalagmite preserves a record of rainfall in this region. It shows that the vital rains of the Asian monsoon weakened at the time of the downfalls of the Tang, Yuan and Ming dynasties over the past 1,810 years. These times of strong and weak rains, when compared with Chinese historical records, coincide with periods of imperial turmoil or prosperity, as in the case of the expansion of the Northern Song Dynasty, when harvests were abundant. In the past 50 years, however, industrial soot and greenhouse gases are causing the rains to weaken. Perhaps that is why today's rulers of China are eager to act on climate change. The stalagmite analysis appears in the November 7 Science.