Modern Africa…or prehistoric Britain? anson chu, CC BY

The last time Earth was this hot hippos lived in Britain (that’s 130,000 years ago)

It’s official: 2015 was the warmest year on record. But those global temperature records only date back to 1850 and become increasingly uncertain the further back you go. Beyond then, we’re reliant on signs left behind in tree rings, ice cores or rocks. So when was the Earth last warmer than the present?



To reach a point when the Earth was significantly warmer than today we’d need to go back 130,000 years, to a time known as the Eemian.

For about 1.8m years the planet had fluctuated between a series of ice ages and warmer periods known as “interglacials”. The Eemian, which lasted around 15,000 years, was the most recent of these interglacials (before the one we’re currently in).

Although global annual average temperatures were approximately 1 to 2˚C warmer than preindustrial levels, high latitude regions were several degrees warmer still. This meant ice caps melted, Greenland’s ice sheet was reduced and the West Antarctic ice sheet may have collapsed. The sea level was at least 6m higher than today.



We know from air bubbles in ice cores drilled on Antarctica that greenhouse gas concentrations in the Eemian were not dissimilar to preindustrial levels. However orbital conditions were very different – essentially there were much larger latitudinal and seasonal variations in the amount of solar energy received by the Earth.




During the Optimum, those carbon dioxide concentrations were the predominant driver of climate change. Global average temperatures were 2 to 4˚C warmer than preindustrial values, sea level was around 20m higher and there was an expansion of tropical vegetation.

However, during the later Miocene period CO2 declined to below preindustrial levels, but global temperatures remained significantly warmer. What kept things warm, if not CO2? We still don’t know exactly – it may have been orbital shifts, the development of modern ocean circulation or even big geographical changes such as the Isthmus of Panama narrowing and eventually closing off – but it does mean direct comparison with the present day is problematic.

Currently orbital conditions are suitable to trigger the next glacial inception. We’re due another ice age. However, as pointed out in a recent study in Nature, there’s now so much carbon in the atmosphere the likelihood of this occurring is massively reduced over the next 100,000 years.