Dark Land Surfaces Allow for Refugia That Could Support Photosynthetic Life on the Surface of Snowball Earth

Abstract Photosynthetic eukaryotic algae survived the Neoproterozoic Snowball Earth events, indicating that liquid‐water refugia existed somewhere on the surface. We examine the potential for refugia at the coldest time of a snowball event, before CO 2 had risen and with high‐albedo ice on the frozen ocean, before it became darkened by dust deposition. We use the Community Earth System Model to simulate a “modern” Snowball Earth (i.e., with continents in their current configuration) in which the ocean surface has frozen to the equator as “sea glaciers”, hundreds of meters thick, flowing like ice shelves. Despite global mean surface temperatures below −60°C, some areas of the land surface reach above‐freezing temperatures seasonally because they are darker than the ice‐covered ocean. With low CO 2 (10 ppm) and land‐surface albedo characteristic of bright sand‐deserts (0.4), 0.1 percent of the land surface could host liquid water seasonally; this increases to 12 percent for darker land of albedo characteristic of polar deserts (0.2). Given a water source to these locations, such as a narrow bay intruding from the ocean like the modern Red Sea, or summer precipitation or melt of nearby glaciers, we argue that photosynthetic life would have the potential to survive on or near warm, bare land. The abundance of warm land and consequently potential refugia increases more strongly in response to reducing the land albedo than to higher CO 2 , for the same global radiative forcing, due to the concentration of the forcing over land.