Reporter 413, 26 January 1998

South Pole fossils reveal global warming is ancient history

TV weather forecasters may have difficulty in telling us whether it is going to rain or shine tomorrow, but a University geologist can describe exactly what the weather was doing – millions of years ago.

By studying the rings of tree fossils, Earth Sciences lecturer Dr Jane Francis can trace temperature changes during an entire year. In the process, the fossilised wood has told her that those who think global warming is new are barking up the wrong tree.

Unlikely as it seems today, the Earth was once warm enough for plants to grow at the South Pole. By studying fossils from trees and twigs collected during several expeditions to Antarctica, Dr Francis has gained some remarkable insights into what the climate might have in store for us in the future.

“The Earth has two stages,” she explains. “There is the greenhouse phase, when there is no ice at all. That’s happened several times before throughout the last 500 million years. It is interspersed with the second stage, the ice house, when there are ice caps at the poles.”

For most of the past 30 million years we have been in the ice house phase. But around two to three million years ago the Earth warmed up enough to melt the ice and allow trees to grow at the South Pole.

This Greenhouse period, when Antarctica was covered in thick forest, lasted a relatively short time - perhaps several tens of thousands of years. Then the ice sheets returned and completely covered the land once again.

By studying the rings of fossils dating from this period, in a pioneering technique she helped develop, Dr Francis has been able to chart the climate changes which took place during the lifetime of these mature trees. She can tell if it was a wet spring or a long winter, and she can discover the likely temperatures throughout the year. Remarkably, the average annual temperature in Antarctica at that time was about minus-ten-degrees-centigrade, with the summer being above freezing. Today it gets as cold as about minus-80-degrees-centigrade in the winter.

All very interesting, no doubt, but where does this knowledge actually get us? It helps us put recent discussions about global warming into a geological context, which could contribute to a better multi-disciplinary understanding of climate challenges ahead.

“We know that Antarctica was once much, much warmer, two to three million years ago,” says Dr Francis. “Although this was a massive change, the Earth was still able to switch back into its cycles of cold and warm. People are scared about global warming today, but the fact is we are still in an ice house although it is a naturally warming phase.

“We know from geological evidence that the Earth warms up and cools down again within cycles. What we don’t know is how far the Earth could warm up but still stay in an ice house phase.”

So the big question is, during an inter-glacial warming phase – as we are in at the moment – can the Earth carry on with its normal cycles? Or will the extra CO2 emissions that are being pumped into the atmosphere push the Earth’s natural systems over the edge?

“The big problem is that we just don’t know enough about how the Earth’s climate system works,” she admits. “To be honest, I don’t think anybody knows, although we are learning more every day.”

One thing is for sure, though. Sensationalist media reporting – such as that which greeted Dr Francis’ paper on the subject at last year’s British Association conference – certainly doesn’t help deepen our understanding.

“Some media coverage of global warming has certainly been a little bit dramatic,” she says. “I’m not saying that we shouldn’t try to curb CO2 emissions. But we need to see it in context and understand how the climate system works. The Earth is a very powerful thing, more powerful than all of us.”

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