Preprints
https://doi.org/10.5194/egusphere-2023-383
https://doi.org/10.5194/egusphere-2023-383
24 Mar 2023
 | 24 Mar 2023

Simulated responses of soil carbon to climate change in CMIP6 Earth System Models: the role of false priming

Rebecca M. Varney, Sarah E. Chadburn, Eleanor J. Burke, Andy J. Wiltshire, and Peter M. Cox

Abstract. Reliable estimates of soil carbon change are required to determine the carbon budgets consistent with the Paris climate targets. This study evaluates projections of soil carbon during the 21st century in CMIP6 Earth System Models (ESMs) under a range of atmospheric composition scenarios. In general, we find a reduced spread of changes in global soil carbon (ΔCs) in CMIP6 compared to the previous CMIP5 model generation. However, similar reductions were not seen in the derived contributions to ΔCs due to both increases in plant Net Primary Productivity (NPP, named ΔCs,NPP) and reductions in the effective soil carbon turnover time (τs, named ΔCs,τ). Instead, we find a strong relationship across the CMIP6 models between these NPP and τs components of ΔCs, with more positive values of ΔCs,NPP being correlated with more negative values of ΔCs,τ. We show that this emergent relationship is the result of 'false priming', which leads to a decrease in the effective soil carbon turnover time as a direct result of NPP increase and occurs when the rate of increase of NPP is relatively fast compared to the slower timescales of a multipool soil carbon model. The inclusion of more soil carbon models with multiple pools in CMIP6 compared to CMIP5, therefore seems to have contributed towards the reduction in the overall model spread in future soil carbon projections.

Rebecca M. Varney et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on egusphere-2023-383', Anonymous Referee #1, 27 Apr 2023
  • RC2: 'Comment on egusphere-2023-383', Anonymous Referee #2, 13 May 2023

Rebecca M. Varney et al.

Rebecca M. Varney et al.

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Short summary
This study evaluates soil carbon projections during the 21st century in CMIP6 Earth System Models. In general, we find a reduced spread of changes in global soil carbon in CMIP6 compared to the previous CMIP5 generation. The reduced CMIP6 spread arises from an emergent relationship between soil carbon changes due to change in plant productivity and soil carbon changes due to change in turnover. We show that this relationship is consistent with 'false priming' under transient climate change.