THREE million years ago the world was much warmer than today, yet carbon dioxide levels were only marginally higher. So what reset the global thermostat? Climate modellers now think changes in polar ice cover played a key role.
Atmospheric CO2 levels during the Pliocene 3 million years ago were 400 parts per million – only slightly higher than today’s 370 ppm, but global temperatures averaged several degrees warmer.
To find out why, Alan Haywood and Paul Valdes, then at the University of Reading, UK, plugged data on Pliocene temperatures into a computer model that simulates interactions between the ocean and…
