Chill we meet again

ON a small TV screen, BBC forecaster Paul Hudson is giving a weather bulletin.

"Welcome to the UK in Two Million Years BC," he says cheerily. "Although the weather has been stable for 700,000 years, things are about to change."

His hand gestures across a weather map of Britain. "We're in for some glacial conditions. There will be biting winds straight from the Arctic and temperatures might drop to -20 degrees C. For the next 60,000 years, it might be best to move to southern Europe."

Welcome, in fact, to the Yorkshire Museum's newest exhibition, Ice Age. This is a fun and informative guide to the past two million years, a period generally known as the Great Ice Age.

Throughout that time, the great ice caps at the north and south poles have alternately grown and shrunk; then grown and shrunk again. Each time the northern ice cap has grown, Britain has been covered with ice sheets up to 1,000 metres thick. Each time it has retreated, Britain has shaken itself free of the ice, and at times has been so warm it has been home to elephants, hippos, rhinos and other animals more usually associated with Africa.

The warm spells, each of which lasted about 40,000 years, are known as interglacial periods, and we're in the middle of one right now.

The last time the great glaciers retreated from our landscape was about 10,000 years ago. Yesterday, in geological terms. Rather longer ago when viewed from our own perspective - the last ice retreated 8,000 years before the first Roman set foot in Britain.

It may have retreated long before there were any historians to record its going: but the ice left its mark. It shaped our geography; it dictated the kind of plant and animal life which inhabits these shores to this day; it even helped determine the development of human culture.

This great little exhibition sets out to show you how - using evidence gleaned throughout our region. The bones of hippo, deer, rhino and bison, all recovered from a cave near Kirbymoorside; strange, scarred rocks and boulders left behind by the retreating ice; the evidence of mankind's growing sophistication, in the form of ever-more-refined flint arrowheads recovered from a period of time spanning tens of thousands of years.

Paul Hudson introduces you to the exhibition, with that weather report on a TV situated in the museum's entrance hall.

You then pass through into the exhibition proper, to be greeted by a giant wall of discarded fridges, 50 altogether. They symbolise ice and cold, explains the museum's curator of geology Camilla Nichol, but also environmental degradation, climate change and the role played by CFCs in global warming.

This is not only an eye-catching gimmick, however. Open the doors of fridges in the base of this fridge mountain, and you can discover a host of fascinating facts about the Ice Age.

Such as that as recently as 14,000 years ago, the ice over northern Scotland was 3km thick. Scotland, in fact, is still rising as it recovers from the ice's weight, causing England to sink like the down end of a see-saw.

Here, you can also learn here about the odd variations in the Earth's orbit around the sun, wobbles which are known as Milankovitch cycles and which are one of the causes of the regular advance and retreat of the ice (see panel).

From the fridge mountain, you enter the gallery known as The Big Freeze. Cool, ice-blue columns line an 'ice tunnel' which takes you through a bare landscape of boulders, many of them 'erratics', lumps of rock carried often hundreds of miles by ice and dumped in our region when the ice retreated.

A brilliant sound-track features the sound of footsteps sinking with a satisfying crunch into deep snow, a whistling arctic wind and the creaking and groaning of glaciers. You learn how creatures such as arctic foxes, snowy owls and mammoths adapted to life in the cold; and look at the plant and animal remains that prove our region was once in the grip of the big freeze.

Next up is the cave gallery. Caves are vital to our understanding of the ice ages, says Camilla. Elsewhere, the ice swept away much of the plant and animal remains that would have allowed us to build up a picture of what lived through the ice. In the caves, however, where the ice could not penetrate, these remains were preserved.

Centrepiece of the cave gallery is the section devoted to Kirkdale Cave near Kirkbymoorside. In 1821, quarrymen were working there when they discovered, buried in the floor, broken up bits of bone.

These proved to be the chewed-up remains of elephant, hippo, giant deer, rhino and bison - as well as hyena jawbones. The debate raged as to how they got there. One theory held that they had been carried there in Noah's flood. Geology professor William Buckland, however, insisted that the cave had been a hyena den, and that it could have been in use for thousands of years.

We now know that the remains date to about 125,000 years ago, a relatively warm period.

The next gallery is the hot zone, which details the kind of plant and animal life that thrived in the warmer, interglacial periods. A giant cave bear snarls at you from one wall; a grey wolf pounces on a hare by another. An enormous mammoth tusk hangs beneath a painting of a primitive, prehistoric hut - itself made with a frame of mammoth bones, like something from a Conan film.

Here you can also follow the process of human development.

The earliest stone tools found locally, dating to about 500,000 years ago, were big, heavy affairs, says Camilla. The game those early men were hunting was big - mammoth, giant deer - and the killing implements needed to be big, too.

Over the millennia, the tools get smaller and finer, until by about 10,000 years ago they were finely-wrought slivers of flint economically chipped from larger pieces of stone.

There were several reasons for this change. The larger game was clearly disappearing from our shores by then, perhaps as a result of hunting by man. At the same time, the human population was growing. So resources were scarce and precious flint had to be used economically, each piece producing as many blades as possible.

Final stop is the ice lab. Here, you put on a white coat and become a scientist, peering through microscopes at tiny pollen grains that provide evidence for the types of plant life that once thrived here, and studying real bones, teeth and rocks discovered throughout the region that help us piece together what life was like during the last Big Freeze.

Ice Age at the Yorkshire Museum runs from tomorrow until December 31. Entry to the museum is £4 adults, £3 concessions, £2.50 children, £9 family ticket. Free admission for York Card holders.

There will be a series of talks given by experts on the Ice Age at the museum over the coming months. Call the museum on 01904 687687 to find out more.

Global warming and the Great Ice Age

Strictly speaking, we're still in the middle of the Great Ice Age which has lasted for two million years. Sure, we are in one of the warm, interglacial periods - and experts reckon it will be about 20,000 years before the ice returns. But return it will.

That being the case, why do we need to worry about global warming?

True, says Dr Rob Marchant, an expert on the impact of human activity on the environment, if we wait long enough the return of the ice will probably be more than enough to compensate for the heating effect of mankind's activities.

"But 20,000 years is a long time to wait," he says.

Until then, if we don't curb our global warming acctivities, we will have to suffer the consequences. Planet earth will not be much harmed by the effects of our activity, says Prof Phil Ineson of the Stockholm Environmental Institute, an environmental research group based at York University. Even organisms such as bacteria won't notice. But we will.

Evidence from ice cores shows that carbobn dioxide levels now are higher than for the past 500,000 years. Over the past 100 years, average global temperatures have risen by something like 0.5 degrees C. That may not sound much, but in geological terms it is a very quick rate of increase, and one that is accelerating.

The result, if it goes unchecked, will vary around the world. Islands and coastal areas will be swamped as sea-levels rise, while in some inland areas there may be severe droughts.

Ironically, the effect of global warming here could be to make Britain colder. As the polar ice caps melt, that could disrupt the flow of the Gulf Stream, which brings warm waters across the Atlantic to heat our shores. The result: temperatures here could plummet.

"One kilometre of ice over our heads?" says Prof Ineson, half-seriously. "I've never tried it, but I don't think it would be much fun."

Ice facts

- Last time the ice melted, global sea-levels rose at a rate of 2.5 metres every 100 years

- Insects which live in Siberia today at temperatures of -45C once lived in Manchester

- Two million years ago the sea off Bridlington was as warm as that off Morocco today

Updated: 09:43 Friday, May 27, 2005