Low atmospheric CO 2 levels during the Little Ice Age due to cooling-induced terrestrial uptake

• Published in: Nature Geoscience
• Main Authors: Rubino, M, Etheridge, DM, Trudinger, CM, Allison, CE, Rayner, PJ, Enting, I, Mulvaney, R, Steele, LP, Langenfelds, RL, Sturges, WT, Curran, MAJ, Smith, AM
• Format: Article in Journal/Newspaper
• Language: English
• Published: Nature Publishing Group 2016
• Subjects: Earth Sciences; Atmospheric Sciences; Climate Change Processes; Dronning Maud Land; Antarc*; Antarctica; ice core
• Online Access: https://doi.org/10.1038/NGEO2769; http://ecite.utas.edu.au/114870

Low atmospheric carbon dioxide (CO 2 ) concentration during the Little Ice Age has been used to derive the global carbon cycle sensitivity to temperature. Recent evidence confirms earlier indications that the low CO 2 was caused by increased terrestrial carbon storage. It remains unknown whether the terrestrial biosphere responded to temperature variations, or there was vegetation re-growth on abandoned farmland. Here we present a global numerical simulation of atmospheric carbonyl sulfide concentrations in the pre-industrial period. Carbonyl sulfide concentration is linked to changes in gross primary production and shows a positive anomaly during the Little Ice Age. We show that a decrease in gross primary production and a larger decrease in ecosystem respiration is the most likely explanation for the decrease in atmospheric CO 2 and increase in atmospheric carbonyl sulfide concentrations. Therefore, temperature change, not vegetation re-growth, was the main cause of the increased terrestrial carbon storage. We address the inconsistency between ice-core CO 2 records from different sites measuring CO 2 and δ 13 CO 2 in ice from Dronning Maud Land (Antarctica). Our interpretation allows us to derive the temperature sensitivity of pre-industrial CO 2 fluxes for the terrestrial biosphere ( γ L = −10 to −90 Pg C K −1 ), implying a positive climate feedback and providing a benchmark to reduce model uncertainties.