While north froze NZ might have stayed temperate

By SIMON COLLINS, science reporter

New Zealand scientists have found evidence that the Southern Hemisphere may have escaped the extremes of the last Ice Age which froze much of Europe, Russia and North America.

The new evidence, if confirmed by further research, would force a rethink of models for the effect of rising carbon dioxide emissions on the global climate.

It would mean climatic forces in different parts of the world are much more complex than conventional thinking has assumed, producing uncertain feedbacks that might either weaken global warming or push it to catastrophic levels.

Until now, scientists have assumed that the whole planet suffered the effects of the last Ice Age between about 78,000 and 11,000 years ago, when temperatures in the Northern Hemisphere were about 6C or 7C colder than they are now.

In the coldest periods, such as the "Younger Dryas" event when the Gulf Stream is believed to have stopped warming Europe about 13,000 years ago, temperatures in Europe dropped to as much as 15C below today's levels.

But the new evidence from the glacial valleys of the Southern Alps suggests that New Zealand might never have been colder than about 2C below present temperatures during the northern Ice Age.

Dr James Shulmeister, an Irish-born geologist at Canterbury University, believes the whole Southern Hemisphere might have escaped with no more than this mild cooling.

"There are only two mid-latitude places in the Southern Hemisphere where glaciers advanced. One is here, the other is in Chile," he said.

"There is a huge scientific bunfight here and in Chile about what the pattern of glaciation was."

At this stage the evidence is still highly preliminary. It is based on the kind of rock formations the glaciers left when they retreated up the Southern Alps, and on the fossilised remains of tiny beetles that are known to live only at certain temperatures.

Dr Shulmeister said the vast ice sheets that covered much of the Northern Hemisphere in the Ice Age left behind huge piles of rock at the furthest points they got to before they melted.

In New Zealand, the rock piles are much smaller.

"Everything here is more to do with flash floods and running water coming out of underneath the glaciers," he said.

"In areas where the glaciers reached, there are very small glacial deposits and huge river and lake deposits, and even within the glacial deposits they have a lot of stratified [water-deposited] material.

"In New Zealand the material may have been bulldozed by ice but there was still tons of water round the landscape, so it simply can't have been that cold."

Dr Maureen Marra, a Tuhoe and Ngati Awa geologist born at Waimana in the eastern Bay of Plenty, has found that the beetles that lived in the Rakaia valley west of Christchurch in the coldest period of the Ice Age would not have survived there if the temperature were more than about 2C colder than today.

In the Awatere valley near Blenheim, she found fossilised beetles, suggesting that the temperature might once have been between 3.5C and 5C colder than it is now - still much less extreme than the Ice Age in Europe.

At Waiorongomai in Palliser Bay east of Wellington, she found 120,000-year-old remains of beetle species that are found today between Cape Reinga and Tauranga, where the modern temperatures are 1.6C to 2.5C warmer in summer and 2.3C to 3.2C warmer in winter than at Palliser Bay.

"They shifted down to the south because it was too hot for them up north," she said. "The beetle fossils from that site indicate that it was 1.5C to 3C warmer about 120,000 years ago."

Dr Shulmeister, Dr Marra, Auckland beetle expert Dr Rich Leschen and other scientists in New Zealand, Australia and the United States are now using a $590,000 grant from the Royal Society's Marsden fund to test a theory that glacial advances in New Zealand are due more to higher snowfall during periods of strong westerly winds than to extreme cold.

"It might still have been slightly colder," Dr Shulmeister said.

"The ice built up because it was a little bit colder. But it was still very wet, so the glaciers expanded, largely under the influence of increased snowfall rather than through the influence of increased cooling."

Mild south

* New evidence from Southern Alps suggests NZ might never have been colder than about 2C below present temperatures during the northern Ice Age between 78,000 and 11,000 years ago.

* The Southern Hemisphere may have escaped with no more than mild cooling.

University of Canterbury:
Quaternary Paleoecology and Paleoclimatology