The question of why atmospheric concentrations of CO2 fall during ice ages, and where that CO2 is stored, seems to have been answered by Swiss and German scientists. Using a new method of measuring isotopes in CO2 trapped in Antarctic ice cores, the scientists determined that in periods of global cooling, the oceans absorb more CO2 and store it deep underwater. As the Earth warms because the tilt of its axis enables it to absorb more energy from the sun, changes in ocean circulation transport CO2 from the deep sea to the surface, where it is released into the atmosphere. The Swiss and German scientists were able to determine through an isotopic “CO2 fingerprint” that the released carbon dioxide came from the deep ocean. The research, published in Science, holds important lessons for climate science today, since atmospheric concentrations of CO2 — now close to 400 parts-per-million — are higher than they have been in 800,000 years and are warming the planet. Since warmer oceans absorb less CO2 than colder oceans, the mechanism of deep-sea storage of CO2 could be disrupted, further increasing carbon dioxide concentrations in the atmosphere.