Low atmospheric CO2 levels during the Little Ice Age due to cooling-induced terrestrial uptake

M. Rubino, D. M. Etheridge, C. M. Trudinger, C. E. Allison, P. J. Rayner, I. Enting, R. Mulvaney, L. P. Steele, R. L. Langenfelds, W. T. Sturges, M. Curran, A. M. Smith

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Abstract

Low atmospheric carbon dioxide (CO2) 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 CO2 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 CO2 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 CO2 records from different sites measuring CO2 and δ13CO2 in ice from Dronning Maud Land (Antarctica). Our interpretation allows us to derive the temperature sensitivity of pre-industrial CO2 fluxes for the terrestrial biosphere (γL = -10 to -90 Pg C K-1), implying a positive climate feedback and providing a benchmark to reduce model uncertainties.

Original languageEnglish
Pages (from-to)691-694
Number of pages4
JournalNature Geoscience
Volume9
Issue number9
Early online date25 Jul 2016
DOIs
Publication statusPublished - Sep 2016

Keywords

  • carbon cycle
  • palaeoclimate
  • ice cores
  • carbonyl sulphide
  • COS
  • Little Ice Age

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