Simulating Continental Dust on a Hard Snowball Earth: 2. Climatic Effect of Dust

Geological records indicate that Earth may have experienced at least two global‐scale glaciations during the Cryogenian Period (720–630 million years ago), known as snowball Earth events. This study quantifies the radiative forcing of continental dust and evaluates its capacity to reduce the critical CO 2 concentration required for snowball Earth deglaciation. We find that atmospheric dust induces a relatively modest global‐mean radiative forcing of about 0.4–1.5 W m −2 at the top of the atmosphere. The surface‐deposited dust lowers global‐mean surface albedo by about 0.06, corresponding to a larger radiative forcing, ∼10 W m −2 . In local regions, the reduction of surface albedo can reach 0.2–0.3 and its corresponding radiative forcing is ∼30–50 W m −2 . When the continental ice sheet is not considered, the CO 2 threshold without dust is ∼4–7 times that with dust. As the ice sheet is included, the CO 2 threshold without dust is ∼1.5–2.0 times that with dust, indicating a moderate role of continental dust. It is worth noting that this work does not consider the process that dust deposited over sea ice would be transported to deep tropical net‐sublimation regions by sea glacier dynamics, which would further decrease the CO 2 threshold (Abbot and Pierrehumbert, Mudball: Surface dust and Snowball Earth deglaciation, JGR‐Atmos, 2010, 115, D03104) and should be explored in the future.