Ice age thermostat prevented extreme climate cooling

Source: Science Daily

During the ice ages, an unidentified regulatory mechanism prevented atmospheric carbon dioxide concentrations from falling below a level that could have led to runaway cooling, reports a team of researchers. The study suggests the mechanism may have involved the biosphere, as plants and plankton struggled to grow under very low carbon dioxide levels.

https://www.sciencedaily.com/releases/2017/03/170314093054.htm