Interstadials

Interstadials are relatively warm periods that interrupt glacial phases within Earth's Quaternary ice ages. They are shorter than interglacials and cooler than full interglacial periods. In the last glacial cycle, for example, the climate swung between stadials (colder intervals) and interstadials (warmer intervals), with interstadials lasting from centuries to several thousand years.

Evidence comes from ice cores, marine and terrestrial records. In Greenland ice cores, interstadials appear as rapid stepwise increases in temperature-sensitive isotopic proxies (for example, δ18O and related measures) and rises in gas concentrations such as CO2 and CH4. Marine sediment cores show shifts in sea surface temperature and productivity, consistent with warmer conditions. Pollen, plant and lake-sediment records also reflect changes in vegetation during interstadials.

Most interstadials are linked to variability in the Atlantic Meridional Overturning Circulation, and consequently shifts in North Atlantic heat export. The progression often involves a relatively fast transition from a stadial to an interstadial, followed by a more gradual cooling back to a stadial state. In some records, the interstadial phase corresponds to Dansgaard–Oeschger events, rapid warmings seen in Greenland ice that are accompanied by a trans-Atlantic climate signal.

Examples include the Bølling-Allerød interstadial in the late Pleistocene, a prominent warm interval just before the Younger Dryas cooling. While interstadials are a common feature of glacial periods, their timing and synchronicity vary by region; they are not identical in all parts of the globe and are distinct from longer interglacial periods.