WILL GREENHOUSE WARMING LEAD TO NORTHERN-HEMISPHERE ICE-SHEET GROWTH

ALTHOUGH model simulations predict a higher mean global temperature by the middle of the next century in response to increased atmospheric concentrations of greenhouse gases 1, the response of the cryosphere to specific changes in latitudinal and seasonal temperature distribution is poorly constrained by modelling 2,3 or through instrumental measurements of recent variations in snow cover 4 and ice thickness 5,6. Here we examine the recent geological record (130 kyr to present) to obtain an independent assessment of ice-sheet response to climate change. The age and distribution of glacial sediments, coupled with marine and terrestrial proxy records of climate, support arguments that initial ice-sheet growth at the beginning of the last glacial cycle occurred at high northern latitudes (65-80-degrees-N) under climate conditions rather similar to present. In particular, the conditions most favourable for glacier inception are warm high-latitude oceans, low terrestrial summer temperature and elevated winter temperature. We find that the geological data support the idea that greenhouse warming, which is expected to be most pronounced in the Arctic and in the winter months, coupled with decreasing summer insolation 7 may lead to more snow deposition than melting at high northern latitudes 8 and thus to ice-sheet growth.