Instability in the geological regulation of Earth’s climate

Negative feedback between climate and atmospheric CO2, as mediated via weathering of silicate minerals, is thought to provide the dominant regulation of Earth’s climate on geological timescales. In contrast, we show here that faster feedbacks involving organic matter are critical and create unexpected instability in the system. Specifically, using an Earth system model, we show how organic carbon burial, amplified by climate-sensitive phosphorus feedbacks, can dominate over silicate weathering, inducing a cooling ‘over-shoot’ and, paradoxically, an ice age in response to massive CO2 release. This instability in the Earth system is most strongly expressed in the model at intermediate redox states of the ocean and atmosphere, offering a novel explanation for the occurrence of past ‘snowball’ climates as the Earth’s surface became appreciably oxygenated.