WELSH academics believe they have found a vital key to the climate switch, explaining why Antarctica went into a “deep freeze” 34 million years ago.
The team of scientists from Cardiff University and National Museum Wales have been studying ice sheet formation in the frozen continent.
They are hoping that greater understanding of one of the most important climatic shifts in the Earth’s history could provide clues about future climate change.
Today they published new evidence showing how computer models predicting the onset of climate change are even more accurate than previously thought.
Dr Carrie Lear, lecturer in palaeoceanography, said her team – bizarrely working in Africa – found new evidence of climate change which helps explain the original appearance of the Antarctic ice sheet.
She explained, “We have been out to the African bush where we have been able to drill for microfossils that were once under the sea, to construct records of temperature and ice volume over the interval of the big climate switch.
“It was not easy drilling 100m into the desert with man-eating lions roaming around, and such mapping can take a long time.
“But these new records show that the world’s oceans did cool during the growth of an ice sheet.
“You could call it a time of global cooling, which was the opposite of the global warming we are seeing today.
“And that volume of ice would have fitted onto Antarctica; so now the computer models of climate and the past climate data match up.”
Dr Lear and her team at Cardiff have presented their new temperature records using the ancient sea floor mud that they recovered from Tanzania, East Africa.
The Welsh researchers made their discovery thanks to data collected from the chemistry contained in the shell of small organisms called forams contained in the mud, that reveal that ocean temperatures did in fact cool by about 2.5C.
She added, “Forams are tiny animals the size of a grain of sand but they are great tools for studying climates of the past.
“By analysing isotopes and the metals in their shells, we can figure out how the climate changed because when it is warmer they contain more magnesium.
“And they can tell us how ocean temperatures changed through time.
“We have found them at different stages and they help us to learn about the uncertainties of our future greenhouse climate.
“These new records help resolve a long-standing puzzle regarding the extent of ice-sheet growth versus global cooling, and bring climate proxy records into line with climate model simulations.”
She said all previous temperature records showed no evidence of the oceans cooling at this time.
Instead they had suggested that the ocean had actually warmed up, presenting a confusing picture of the climate system which has long been a mystery in palaeoclimatology.
The team at Cardiff University’s School of Earth, Ocean and Planetary Sciences will now look for evidence of the ultimate cause of the global cooling using the forams.
They believe the prime suspect is a gradual reduction of CO2 in the atmosphere, combined with a “trigger” time, when Earth’s orbit around the sun made Antarctic summers cold enough for ice to remain frozen all year round.
Dr Lear said, “Before the arrival of the ice sheet, CO2 levels were double what they are today, at a level that is not too different from where they could be in 100 years’ time if we don’t offset CO2 emissions.
“We know that CO2 is the main greenhouse gas responsible for global warming,” he added.
“We aim to find out how quickly the warming will occur and which places will be affected more than others.
“And these new records will help us to be even more confident about future predictions.”