Global average temperatures were 10-12 Â°C hotter than today. Most places on land were so hot that humans would risk fatal heat stroke every summer. The geological record shows many ancient changes in climate, including massive ice ages, hot-house conditions, oxygen-free and acidic oceans, and massive extinction events. These changes happened millions of years before humans, most occurred before even primitive mammals, appeared on the scene. Previous climate changes were caused by orbital wobbles, solar fluctuations, and movement of continents. None of those effects are causing the current heating http://sks.to/past. Last updated on 9 March 2012 by dana1981.