新仙女木期（Younger Dryas），是指距今12800年至11500年的一段持续1300年左右的冰期。在此之前地球一直处在温度逐渐升高的间冰期中，由于突然发生了新仙女木事件而导致全球气温骤降，北极冰川南侵。这一时期的得名来自于欧洲北部仙女木属的一种植物，该物种本生活在寒带地区，而对格陵兰冰川的研究却发现，新仙女木期时在低纬度地区都能发现该物种的花粉，从而表明当时气候寒冷，该物种大肆南侵。

新仙女木期冰段是中断自从20000年前末次冰盛期（LGM）以来气候变暖的趋势的一个寒冷时期。在新仙女木期之前还有最老仙女木期与老仙女木期。老仙女木期发生在新仙女木期之前大约1000年，历时约3000年。最老仙女木期的日期是大约距今（BP）18,000至15,000年之间。

The Younger Dryas is a geological period from c. 12,900 to c. 11,700 calendar years ago (BP). It is named after an indicator genus, the alpine-tundra wildflower Dryas octopetala. Leaves of Dryas octopetala are occasionally abundant in the Late Glacial, often minerogenic-rich, lake sediments of Scandinavian lakes. Younger Dryas saw a sharp decline in temperature over most of the northern hemisphere, at the end of the Pleistocene epoch, immediately preceding the current warmer Holocene. It was the most recent and longest of several interruptions to the gradual warming of the Earth's climate since the severe Last Glacial Maximum, c. 27,000 to 24,000 calendar years BP. The change was relatively sudden, taking place in decades, and resulted in a decline of 2 to 6 degrees Celsius, advances of glaciers and drier conditions, over much of the temperate northern hemisphere. It is thought to have been caused by a decline in the strength of the Atlantic meridional overturning circulation, which transports warm water from the equator towards the North Pole, and which in turn is thought to have been caused by an influx of fresh cold water from North America into the Atlantic. The Younger Dryas was a period of climatic change, but the effects were complex and variable. In the southern hemisphere, and some areas of the north such as the south-eastern United States, there was a slight warming.