The climate of the future: clues from three million years ago

James Hutton is generally regarded as the father of modern geology. In the eighteenth century he came up with a theory that revolutionized the science of geology: uniformitarianism, expressed by Charles Lyell as ‘The present is a key to the past’. This has enabled generations of geologists to interpret information gleaned from rocks and sediments by reference to examples existing in the modern environment. Although this remains a corner stone of geology, could the past also be a guide to our future? Certainly this would not surprise an historian; consider the old saying ‘history always repeats itself’. Nonetheless, in geology it is an idea that is only now being fully explored. The driving force behind this new adventure is the changing climate of our planet and our desire to understand, predict and mitigate the effects of future climate change. According to the latest report produced by the Intergovernmental Panel on Climate Change, our planet is running a temperature. Within the next 150 to 350 years, Earth will warm by an extent not seen for millions of years. This warming is a result of the emission of greenhouse gases such as carbon dioxide (CO 2 ) and methane (CH 4 ) into the atmosphere. Rapid climate change has become the disaster scenario for the twenty-first century. Be it cities deluged by giant waves, paradise islands sinking into the oceans, or the corals of the Great Barrier Reef heated-up to extinction, everyone is aware that climate change can have a dramatic effect on the world we live in. In the recent Hollywood movie The Day After Tomorrow, New York was frozen solid as the climate of the Northern Hemisphere took a dramatic turn for the worse. But what evidence do we have for climate change in the past, and how can we use the information stored in the geological record to help us predict what our climate and environment might be like in the future? One of the best places to look is the world of the mid-Pliocene, three million years ago. The mid-Pliocene is the last time in geological history when our planet’s climate was significantly warmer, for a prolonged period, than it is today. So what was the mid Pliocene world like?