A test of the overdue-glaciation hypothesis

According to a new hypothesis, greenhouse-gas concentrations in the atmosphere should have fallen throughout the last several thousand years and caused a significant cooling of Earth's climate, but early anthropogenic emissions of carbon dioxide and methane kept temperatures relatively warm. A further prediction is that ice should have begun accumulating in northeast Canada several thousand years ago. We carry out a preliminary test of this hypothesis by reducing atmospheric CO 2 and CH 4 concentrations to their estimated ‘natural’ levels in an experiment with the GENESIS climate model. In the absence of anthropogenic contributions, global climate is almost 2 °C cooler than today and roughly one third of the way toward full-glacial temperatures. The hypothesis of an overdue glaciation is confirmed, but at a small scale: parts of Baffin Island retain snow cover year-round, and snow cover persists on high terrain in Labrador for 11 months of the year.