Greenhouse-gas fingerprints

Abstract

Short episodes of warming and cooling occurred throughout the last glaciation. An innovative modelling study indicates that ocean-circulation changes produced much of the causative variation in greenhouse gases. Much of what we know about abrupt climate change and tipping points in the climate system comes from polar ice cores1. But these unique data archives provide only a narrow view of the richness of climate dynamics and impacts. Moreover, the origin of the variations in the greenhouse gases associated with the pronounced climate swings during the last ice age, an interval between about 110,000 and 10,000 years ago, remains largely unknown. Hence the significance of computer models in providing a wider perspective. On page 373 of this issue, Schmittner and Galbraith2 present climate-model simulations for an episode of abrupt climate change during the last ice age. Their results show agreement with the palaeoclimatic record3, not only in terms of physical climate variables, but also, remarkably, in changes in the greenhouse gases carbon dioxide (CO2) and nitrous oxide (N2O). The researchers conclude that the interaction of physical and biogeochemical processes in the ocean is largely responsible for the observed variations.