Quantifying negative radiative forcing of non-permanent and permanent soil carbon sinks

Summary

This modelling study addresses the critical question of how reversible soil carbon sequestration should be accounted for in climate mitigation policy by quantifying radiative forcing effects across 500-year timescales. The authors demonstrate that whilst non-permanent CO2 removals do generate cooling effects, their radiative impact is substantially lower than equivalent permanent sequestration. The findings suggest that average annual soil organic carbon balance, rather than rates of gain/loss or sink longevity, is the primary determinant of radiative forcing, providing a basis for unbiased comparison of soil carbon mitigation projects.

UK applicability

These findings are directly relevant to UK soil carbon policy and voluntary carbon market schemes, particularly in evaluating the climate credibility of reversible sequestration practices (e.g., temporary increases in soil organic matter from improved management). The quantitative framework could inform UK guidance on soil carbon accounting and support more rigorous appraisal of soil-based nature-based solutions in national climate commitments.

Key measures

Radiative forcing (W/m²), soil organic carbon balance (annual average over integrated time window), atmospheric CO2 impulse response, carbon sink permanence and reversibility

Outcomes reported

The study quantified radiative forcing effects of reversible and non-reversible soil carbon sinks over a 500-year time horizon using atmospheric CO2 impulse response functions. Results demonstrated that both permanent and non-permanent soil carbon removals generate negative radiative forcing (cooling), but with substantially different magnitudes and temporal dynamics.

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