The short (325 m) Renland ice core from East Greenland was the first ice core to provide a continuous record of ammonium (NH4+) through the whole glacial period. The deep ice cores GRIP and GISP2 from Summit have confirmed that it is representative of the NH4+ deposition on Greenland. We argue that high levels of NH4+ in the ice during periods of warming (at the end of the last glaciation, during Dansgaard/Oeschger events, in MIS 5a and 5c, and during the Eem interglacial) provide evidence for rapid response by high latitude ecosystems and soils since the atmospheric turn-over time of ammonia (including its existence as NH4+) is short. Sources which emit ammonia usually also emit methane. High Greenland NH4+ levels coincide with high global methane concentrations. Northern high latitude biogenic sources are here suggested to contribute significantly to global methane concentrations during periods of warming during the last glacial period. ¿ 2001 American Geophysical Union