Global Warming happened before?
Global Warming has happened before? Higher temperatures on earth are not unknown. The most extreme was the earth's climate in the Upper Cretaceous Period (86 million years ago), which was far warmer than today. The Mean Surface Temperature across the Earth during this time has been estimated as being 11°c warmer than now.
These higher temperatures were as a result of two things: a significantly different layout of the continents that allowed for improved heat circulation in the oceans; and a much higher level of carbon dioxide in the atmosphere at the time - four times higher than today.
The Upper Cretaceous Period has been referred to as a 'greenhouse world' and much of the predictions of what could happen to the environment in the future has been based on our understanding of what the world was like during this time.