White paper: The oldest ice core: A 1.5 million year record of climate and greenhouse gases from Antarctica

Climate scientists have an obligation to provide realistic assessments of how climate will change in the future. Doing so requires accurate models of how the Earth’s climate system works and responds to changes. This in turn requires that we understand all the processes that can occur, and how they interact. This knowledge comes only from studying the past. Ice- core studies in particular have already revolutionized our view of the Earth system, documenting the recent rise of greenhouse gas concentrations beyond historical norms, the existence of abrupt climate changes, and the tight coupling in the past of climate and greenhouse-gas concentrations.

In deep Antarctic ice cores, we can observe that we are currently living in a relatively mild “interglacial” phase within a series of warm/cold oscillations occurring every 100,000 years. These cycles must arise from a strong amplification of weak changes in energy inputs. And we can see that these small changes in input also cause major changes in the partitioning of carbon dioxide and other greenhouse gases between the atmosphere and other reservoirs. However, we still lack understanding of why these processes occur; this means that we still lack crucial knowledge about the natural regulation of carbon dioxide, and about the amplifications that make the climate system so sensitive. Both these factors are important as we try to predict the future.