In early 2017, an international research team made an unexpected discovery beneath the Antarctic ice: Traces of rainforests near the South Pole. In a sediment core, our team unearthed pristinely preserved forest soil from the late Cretaceous greenhouse world, including a dense network of fossil roots and a high diversity of Cretaceous pollen and spores. Our study uniquely illustrates yet unexpected potencies of carbon dioxide as a greenhouse gas and also quite clearly reveals the significance of ice sheet presence for global climate stability.