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<p>Reliable estimates of soil carbon change are required to determine the carbon budgets consistent with the Paris Agreement climate targets. This study evaluates projections of soil carbon during the 21st century in Coupled Model Intercomparison Project Phase 6 (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 (<span class="inline-formula">ΔC_s</span>) in CMIP6 compared to the previous CMIP5 model generation. However, similar reductions were not seen in the derived contributions to <span class="inline-formula">ΔC_s</span> due to both increases in plant net primary productivity (NPP, named <span class="inline-formula">ΔC_s,NPP</span>) and reductions in the effective soil carbon turnover time (<span class="inline-formula"><i>τ</i>_s</span>, named <span class="inline-formula">ΔC_s,<i>τ</i></span>). Instead, we find a strong relationship across the CMIP6 models between these NPP and <span class="inline-formula"><i>τ</i>_s</span> components of <span class="inline-formula">ΔC_s</span>, with more positive values of <span class="inline-formula">ΔC_s,NPP</span> being correlated with more negative values of <span class="inline-formula">ΔC_s,<i>τ</i></span>. We show that the concept of “false priming” is likely to be contributing to this emergent relationship, 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 in NPP is relatively fast compared to the slower timescales of a multi-pool soil carbon model. This finding suggests that the structure of soil carbon models within ESMs in CMIP6 has likely contributed towards the reduction in the overall model spread in future soil carbon projections since CMIP5.</p>