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The last great global warming

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As world leaders gather in the Danish capital Copenhagen to negotiate a successor to the Kyoto Agreement, it’s probably worth pondering on what happened last time temperatures were at levels predicted for the end of this century.  
In 1874, a scientist called Pieter Harting took a number of cores that had been taken around the Dutch city of Amersfoort. The sediments they contained provided a treasure trove of information on an ancient climate.  Not only did the ocean muds Harting find show this part of the Netherlands was once under the sea but the seashells contained therein belonged to species that did not live in the 19th century North Sea. Crucially, some of his fossil species were identical to those living in the Mediterranean, suggesting that the North Sea had been warmer than today. He named the layers ‘Système Eémien’ after the River Eem that flowed alongside Amersfoort. We now know these layers date back to between 130,000 and 116,000 years ago. Although this sounds like an in…