Reconciling ice core CO₂ and land-use change following New World-Old World contact

Ice core records of carbon dioxide (CO₂) throughout the last 2000 years provide context for the unprecedented anthropogenic rise in atmospheric CO₂ and insights into global carbon cycle dynamics. Yet the atmospheric history of CO₂ remains uncertain in some time intervals. Here we present measurements of CO₂ and methane (CH₄) in the Skytrain ice core from 1450 to 1700 CE. Results suggest a sudden decrease in CO₂ around 1610 CE in one widely used record may be an artefact of a small number of anomalously low values. Our analysis supports a more gradual decrease in CO₂ of 0.5 ppm per decade from 1516 to 1670 CE, with an inferred land carbon sink of 2.6 PgC per decade. This corroborates modelled scenarios of large-scale reorganisation of land use in the Americas following New World-Old World contact, whereas a rapid decrease in CO₂ at 1610 CE is incompatible with even the most extreme land-use change scenarios.

Amy C. F. King, Thomas K. Bauska, Edward J. Brook, Mike Kalk, Christoph Nehrbass-Ahles, Eric W. Wolff, Ivo Strawson, Rachael H. Rhodes, Matthew B. Osman