Climate change is a natural process of warming and cooling that has occurred all through the Earth’s history. Throughout historical times, fluctuations in the Earth’s mean temperature have been recorded. During the seventeenth century, the Thames periodically froze over during winter and mini-glaciers were present in the North West Highlands of Scotland. More recently, the 1990s included some of the hottest years ever recorded in the British Isles, and 10 August 2003 was the hottest day ever on record. An annual temperature record for central England has been constructed.
The Earth entered into the most recent comparatively cold period of its history (known as the Pleistocene Ice Age) around 2.6 million years ago. On a geological time-scale, these Ice Ages are relatively rare, covering only 2–3% of the history of our planet. The characteristic feature of the current one (and there is no reason to suppose that it is finished). Drilled in Antarctica, the Vostok ice core provides a temperature record that goes back several hundreds of thousands of years. Beyond about 10 000 years ago, it tells a story of an unstable climate oscillating between short warm interglacial periods and longer cold glacial periods about every 100 000 years – with global temperatures varying by as much as 5 to 8 °C – interspersed by many more short-term fluctuations.
By contrast, global temperatures over the last 10 000 years or so seem to have been much less variable, fluctuating by little more than one or two degrees. In short, the interglacial period in which we live, known as the Holocene, appears (on available evidence) to have provided the longest period of relatively stable global climate for at least 400 000 years. It is almost certainly no coincidence that this is also when many human societies developed agriculture and when the beginnings of modern civilisations occurred. We now shift the focus to the more recent past – the period during which human population growth and the coming of the industrial age began to make their mark on the composition of the atmosphere.
