The general lack of significant changes in mineral soil C stocks during CO 2 ‐enrichment experiments has cast doubt on predictions that increased soil C can partially offset rising atmospheric CO 2 concentrations. Here, we show, through meta‐analysis techniques, that these experiments collectively exhibited a 5.6% increase in soil C over 2–9 years, at a median rate of 19 g C m −2 yr −1 . We also measured C accrual in deciduous...