Global warming may not have ended Ice-Age, says research

Scientists at the University of Sheffield have used fossilised leaves to determine the effect of greenhouse gases on the end of the Ice Age 300m years ago, according to an article published in PNAS.

The study, led by Professor David Beerling, examined fossilised leaves to determine how much carbon dioxide was in the air at various periods during the ice age.

Leaves have pores on their surface called stomata that act as “air holes” and open and close depending on the levels of carbon dioxide in the air. The stomata are wider when there is little carbon dioxide to allow the plants to take in enough carbon dioxide to live. Also, leaves that live in areas with low levels of carbon dioxide have more stomata than those in areas with higher levels.

The fossilised leaves were lycospids, a now extinct plant that flourished in low-lying swamp areas. To determine the levels of carbon dioxide in the air during the ice age Professor Beerling examined how carbon dioxide affected the stomata in a living relative of lycospids, Lycopodium cernuum. From this he was able to use the fossilised leaves to determine how much carbon dioxide was in the air at the beginning, middle and end of the Ice Age.

Professor Beerling explains the results, “We were surprised to see that carbon dioxide levels didn’t rise significantly when the ice sheets began to melt. This suggests that another factor, rather than global warming, was responsible for the end of the Ice Age. It may have simply been that that South Pole was moving at this time and moved into slightly warmer climates.”