What happens to the tropics when global temperatures increase? Whilst it is well established that the polar regions warm dramatically during time intervals of global warmth. For example, 3 million years ago Ellesmere Island (79 degrees north) had a mean annual temperature that was 19°C warmer than today. However, what happens in the tropics is a bit of a mystery. Whilst Ellesmere Island was noticeably warmer 3 million years ago, the tropics appeared to be the same as today. However, a new study by Charlotte O'Brien and colleagues published in Nature Geoscience, has shown that the tropics 3 million years ago were warmer than today - by around 2°C. Whilst 2 is less dramatic than 19, this new result shifts our thinking on how heat is dispersed in the Earth system.
The western warm pools of the Atlantic and Pacific oceans are a critical source of heat and moisture for the tropical climate system. Over the past five million years, global mean temperatures have cooled by 3–4 °C. Yet, present reconstructions of sea surface temperatures indicate that temperature in the warm pools has remained stable during this time.