The current interglacial is nearing its conclusion, according to conventional wisdom. Once the world made it past a few centuries' worth of greenhouse warming, the climate would start getting cold again. This conclusion rested on the assumption that the current interglacial would persist only about 10,000 years, the length of the last interglacial, which occurred 120,000 years ago. Recent studies, however, have demonstrated that the last interglacial does not make a good model for understanding the present. Instead, stage 11 has emerged as the better example.
Scientists base the comparison on features of Earth's orbit.
Every 400,000 years, the shape of the orbit varies from a squashed circle to a more nearly perfect one. Modern times resemble stage 11 in that the orbit is nearly circular, which tends to dampen the climatic influences of other orbital factors, says Andr L. Berger of the Catholic University of Louvain in Belgium, who presented his findings at the recent AGU meeting. In simulations using a computerized climate model, Berger and his colleagues found that the orbital effects would keep Earth out of an ice age for 30,000 years, producing an exceptionally long interglacial matched only by stage 11. For the next few thousand years, he says, the sunlight variations will be rather weak. The insolation is not going to vary that much.