Mid-Latitude Warming Amplified the Runaway Transition to the Neoproterozoic Snowball Earth

The onset of the Neoproterozoic Sturtian glaciation (~717 Ma) represents a fundamental climatic paradox: the silicate weathering negative feedback should have stabilized Earth’s climate by suppressing CO2removal as temperatures dropped, theoretically preventing a runaway Snowball Earth state. Although the low-latitude concentration of Cryogenian continents may have weakened this feedback, the specific mechanism that sustained intense weathering sufficiently to cross the critical ice-albedo threshold remains elusive. Here, we present high-resolution magnesium isotope records (δ26Mgsili) from South China (~30°N) that capture the pre-glacial to glacial transition. Contrary to the expectation of a slowdown under global cooling, our data reveal a pronounced intensification of silicate weathering precisely at the glacial onset. We propose that this anomaly was driven by high-latitude ice-sheet expansion, which altered the planetary heat distribution and induced relative warming in the ice-free mid-latitudes. This regional warming sustained vigorous silicate weathering and atmospheric CO2 drawdown, creating a destabilizing positive feedback loop that overwhelmed the planetary thermostat. Our findings identify mid-latitude warming as a critical amplifier in the Snowball Earth initiation, offering a deep-time perspective on how climate systems can bypass stabilizing feedbacks near tipping points.