IPCC climate change predictions were spot-on, new study affirms
A team of multinational researchers at University of Southampton has revealed through its analysis that CO2 levels in in the atmosphere millions of years ago support current predictions on climate change from the Intergovernmental Panel on Climate Change (IPCC).
The team analysed 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 around 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.
The researchers studied the relationship between CO2 levels and climate change during a warmer period in Earth’s history and have estimated how the climate will respond to increasing levels of carbon dioxide, a parameter known as climate sensitivity, and also show how it can vary over the long term.
According to Gavin Foster, co-author of the research published in Nature, Earth is still adjusting to the recent rapid increase in CO2 levels caused by human activities, whereas the longer-term Pliocene records document the full response of CO2-related warming.
Foster added that estimates of climate sensitivity lie well within the range of 1.5 to 4.5 degree C increase per CO2 doubling summarised 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 added that their 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.
Richard Pancost from the University of Bristol Cabot Institute added that when they account for the influence of the ice sheets, they confirm that the Earth’s climate changed with a similar sensitivity to overall forcing during both warmer and colder climates.
The research team also analysed climate sensitivity in colder times like the glacial cycles of the last 800,000 years.
Dr Eelco Rohling, of the Australian National University in Canberra, revealed that through their analysis they found that “climate change in response to CO2 change in the warmer period was around half that of the colder period.”
Rohling added that this particular difference is “driven by the growth and retreat of large continental ice sheets” present during ice-age like climates. “These ice sheets reflect a lot of sunlight and their growth consequently amplifies the impact of CO2 changes”, Rohling added.