evidence: Both the northern hemisphere and overall global temperatures actually lagged CO2; in other words, for the world as a whole, warming happened after atmospheric CO2 concentrations increased. The reasons for this are complex and are driven in part by changes in ocean currents as ice ages end. [...] This southern hemisphere warming caused ocean releases of CO2, which, in turn, warmed the entire planet. Shakun et al suggest that the vast majority of the global warming at the end of the last ice age occurred after CO2 increased, though this warming was driven by a combination of albedo (reflectivity) changes and the greenhouse effect. [...] The fact that relatively small changes in external forcings can drive such a large planetary response during ice ages should serve as a cautionary example. This is because human emissions of CO2 and other greenhouse gases push the Earth further out of the range of climate conditions that have characterised the past few million years.