The rapid climate changes at the terminations marking the end of the last glaciation are poorly understood. This study uses the Cambridge two-dimensional atmospheric model to investigate the impact of a large marine sediment slump or permafrost rupture releasing 4000 Tg of CH4 into the high latitudes of the northern hemisphere, with particular emphasis on the evolution of atmospheric CH4 concentrations, which may have led to an associated direct radiative effect of the order of 1 W m-2, persisting for a few decades, because of enhanced levels of atmospheric CH4. The model-generated CH4 concentrations were converted into synthetic ice core signals for 66 ¿N and 85 ¿S, representing Arctic and Antarctic cores, respectively. A range of possible averaging times was considered. The results show that irrespective of the site or enclosure time chosen, with the current sampling interval of ~300 years, it is not possible to discount completely the existence of a spike as a result of the instantaneous release of 4000 Tg of CH4. Detection or refutation of a CH4 spike would, however, be probable if the sampling interval were reduced to around 50--100 years. ¿ American Geophysical Union 1996