ABSTRACT
The geological record contains abundant evidence on the ways Earth's climate has changed in the past and provides important clues on how it may change in the future. The Earth's temperature changes naturally over time scales ranging from decades, to hundreds of thousands, to millions of years. In some cases these changes are gradual and in others abrupt Evidence for climate change is preserved in a wide range of geological settings, including marine and lake sediments, ice sheets, fossil corals, stalagmites, and fossil tree rings. The geological evidence from the 55 million year event and from earlier warming episodes suggests that such an addition is likely to raise average global temperatures by at least 5 to 6°C, and possibly more. In the light of the geological evidence presented it is reasonable to conclude that emitting further large amounts of carbon dioxide into the atmosphere over time is likely to be unwise, uncomfortable though that fact may be.
