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. Several past episodes of rapid carbon cycle and climate change arehypothesised to be the result of the Earth system reaching a tipping pointbeyond which an abrupt transition to a new state occurs. At thePalaeocene–Eocene Thermal Maximum (PETM) at ∼56  Ma and at subsequenthyperthermal events, hypothesised tipping points involve the abrupt transferof carbon from surface reservoirs to the atmosphere. Theory suggests thattipping points in complex dynamical systems should be preceded by criticalslowing down of their dynamics, including increasing temporal autocorrelationand variability. However, reliably detecting these indicators inpalaeorecords is challenging, with issues of data quality, false positives,and parameter selection potentially affecting reliability. Here we show thatin a sufficiently long, high-resolution palaeorecord there is consistentevidence of destabilisation of the carbon cycle in the ∼1.5  Myr priorto the PETM, elevated carbon cycle and climate instability following both thePETM and Eocene Thermal Maximum 2 (ETM2), and different drivers of carboncycle dynamics preceding the PETM and ETM2 events. Our results indicate aloss of “resilience” (weakened stabilising negative feedbacks and greatersensitivity to small shocks) in the carbon cycle before the PETM and in thecarbon–climate system following it. This pre-PETM carbon cycledestabilisation may reflect gradual forcing by the contemporaneous NorthAtlantic Volcanic Province eruptions, with volcanism-driven warmingpotentially weakening the organic carbon burial feedback. Our results areconsistent with but cannot prove the existence of a tipping point for abruptcarbon release, e.g. from methane hydrate or terrestrial organic carbonreservoirs, whereas we find no support for a tipping point in deep oceantemperature.

Reduced carbon cycle resilience across the Palaeocene–Eocene Thermal Maximum