The 1610 CO₂ minimum ("Orbis spike")

node · earth · Global; measured in Antarctic ice cores

Antarctic ice cores record a dip in atmospheric carbon dioxide in the late sixteenth and early seventeenth centuries, reaching a minimum around 1610, of a magnitude usually given as several parts per million. Lewis and Maslin proposed in 2015 that this minimum be adopted as the formal marker of the start of the Anthropocene, on the argument that it is the atmospheric signature of the American population collapse: tens of millions of deaths meant tens of millions of hectares of managed farmland reverting to forest and scrub, and regrowing vegetation drawing down carbon. Koch and colleagues later quantified the abandoned area and concluded the effect was large enough to contribute materially to the observed dip. The proposal is contested on two fronts — whether the land-use signal is big enough relative to ocean and volcanic contributions and to Little Ice Age cooling, and whether 1610 is the right place to put a boundary at all. The stratigraphic body reviewing the question favoured a mid-twentieth-century marker instead, and in March 2024 the relevant IUGS subcommission voted against formalising an Anthropocene epoch. Whatever is eventually decided about the boundary, the underlying observation stands and is remarkable in itself: a demographic catastrophe in one hemisphere is legible in the air trapped in ice at the other pole.