A multinational research team at the University of Southampton has revealed that records of carbon dioxide in the atmosphere millions of years ago support current predictions on climate change from the Intergovernmental Panel on Climate Change (IPCC). By studying the relationship between CO2 levels and climatic change during a warmer period in Earth's history, scientists have been able to estimate how the climate will respond to increasing levels of CO2, a parameter known as climate sensitivity, and also show how it can vary over the long term.
The researchers analyzed new records showing the CO2 content of the Earth's atmosphere between 2.3 to 3.3 million years ago, over the Pliocene. During the Pliocene, the Earth was about 2 degree C warmer than it is today and atmospheric CO2 levels were around 350-400 parts per million (ppm), similar to the levels reached in recent years.
Co-author Gavin Foster said, "Today the Earth is still adjusting to the recent rapid rise of CO2 caused by human activities, whereas the longer-term Pliocene records document the full response of CO2-related warming. Estimates of climate sensitivity lie well within the range of 1.5 to 4.5 degree C increase per CO2 doubling summarized in the latest IPCC report. This suggests that the research community has a sound understanding of what the climate will be like as we move toward a Pliocene-like warmer future caused by human greenhouse gas emissions."
Lead author Miguel Martinez-Boti said, "Our new records also reveal an important change at around 2.8 million years ago, when levels rapidly dropped to values of about 280 ppm, similar to those seen before the industrial revolution. This caused a dramatic global cooling that initiated the ice-age cycles that have dominated Earth's climate ever since."
The findings appear in Nature.