evidence: - The hot house periods described in this article occurred millions and millions of years before humans existed. They have no bearing on whether modern human civilization can cope with the level of warming we are likely to face if we do not stop adding greenhouse gases to the atmosphere. [...] Even while ice sheets covered more and more of Earth’s surface, tectonic plates continued to drift and collide, so volcanic activity also continued. Volcanoes emit the greenhouse gas carbon dioxide. In our current, mostly ice-free world, the natural weathering of silicate rock by rainfall consumes carbon dioxide over geologic time scales. During the frigid conditions of the Neoproterozoic, rainfall became rare. With volcanoes churning out carbon dioxide and little or no rainfall to weather rocks and consume the greenhouse gas, temperatures climbed. [...] Geologists and paleontologists have found that, in the last 100 million years, global temperatures have peaked twice. One spike was the Cretaceous Hot Greenhouse roughly 92 million years ago, about 25 million years before Earth’s last dinosaurs went extinct. Widespread volcanic activity may have boosted atmospheric carbon dioxide. Temperatures were so high that champsosaurs (crocodile-like reptiles) lived as far north as the Canadian Arctic, and warm-temperature forests thrived near the South Pole.