Climate Change 3: History and Current State

© 2013 Elsevier Inc. All rights reserved. Being subjected to different natural and anthropogenic forcings, the Earth's climate changes at a variety of time scales. In the course of the Earth's history, a general cooling trend can be observed. The turn from the generally warm Paleozoic and, especially, Mesozoic epochs to the Quaternary is a marked example of this general cooling. This latter turn has followed by the periodic variations of the Earth's climate in the Quaternary with its alternate glacials and interglacials. The last century and a half are unprecedented in terms of rate of the climate change during the last millennium. As the past epochs represent climate states quite different from the present-day one, they may be useful for validating climate models. For instance, if we compare model simulations and available reconstructions of past epochs with high atmospheric concentration of carbon dioxide, we get that most probable range of the climate model sensitivity to the doubling of the carbon dioxide in the atmosphere is 3.0±1.5. °C