Science: Adventures In The Ice World

There is ice in Greenland that fell as snow 200,000 years ago. And through its study, scientists have started to understand how and why the Earth warms and cools.

It covers one tenth of the Earth's surface, and weighs 33 quadrillion tonnes. In places it is two miles deep, and it is so heavy that it warps the crust of our planet downwards, thousands of feet, like a spoon balancing on the skin of a rice pudding. There are the familiar worlds of land and ocean, and there is this third world; the ice world, or cryosphere, is little visited except by summer skiers, adventurers and scientists. The world of permanent ice, the caps and sheets of the polar regions, and the high mountain glaciers is an alien and inhospitable place; naked and unprotected, a human being would last no longer on the shivering plains of an Antarctic winter than he or she would on the surface of Mars.

Yet ice is as vital to our species as the rainforests and the oceans. Environmental activists and, increasingly, politicians, claim that our appetite for mobility and power is threatening the survival of the ice world. As we burn oil, gasoline and coal, the carbon locked in these fossil fuels over the millennia is released, providing the atmosphere with an unwanted insulating blanket of carbon dioxide, warming and expanding the oceans, and melting the ice, causing flooding and climatic disruption that could, the greenhouse pessimists say, kill millions through disease and famine, and drive millions more away from the coastal cities and coral atolls as they are slowly swamped. It is by studying ice, literally in great depth, that scientists have made the greatest inroads into understanding how and why the Earth periodically warms and cools. By drilling into the polar glaciers we can expose a frozen record of our planet's changing climate, the crystal layers revealing the temperature balance sheet that is the key to understanding the ice ages of the past, and the feared climatic changes of the future.

Every shard of clear blue ice found in the glaciers and ice sheets of Greenland, Iceland and Antarctica began life as snowflakes. If the ice fields of the high latitudes are climatic architecture on a grand scale, then the tiny crystals that fall from the sky are miniature works of fine art. Natural ice is classified by geologists as a mineral, just like quartz, mica or diamond. Like these, it exists not in amorphous blobs of randomly-arranged atoms, but in delicately fashioned multi-faceted crystals. Each mineral crystallises in a different and characteristic way. Quartz into elongated, pyramid-topped prisms; diamond into tetrahedra; pyrites and galena into cubes. Ice, when given space to breathe, forms itself into exquisite six-sided forms, the 120-degree symmetry a reflection of the atomic geometry of water. This angle is a constant, but can lead to an effectively infinite number of possible shapes, from simple hexagonal plates to impossibly intricate branches and reticulations.

Although the starry image of the snow crystal is now ubiquitous - from the symbol denoting how cold your freezer will get, to the air-conditioning button in your car - we have only known about the beauty and symmetry of ice for a little more than a century. In the 1880s, a book called Cloud Crystals, with sketches by "A Lady" was published in the US. The lady had caught snowflakes on a black surface and observed them through a magnifying glass. In 1885, Wilson Alwyn "Snowflake" Bentley, of Jericho, Vermont, began taking photographs of snowflakes through a microscope. Thousands of them were eventually collected in his book Snow Crystals (1931). Today, thanks to the electron microscope, we can see the beauty of frozen water in even greater detail.

It was Bentley who came up with the idea that no two crystals were ever alike. In fact, there is no way of verifying this, and no reason to believe that it is true. There are a whole host of myths about snow and ice, reflecting its strangeness and essential unfamiliarity. There is the story that the Inuit have a thousand words for snow, or at least a hundred. In fact, there seem to be around a dozen words in each of the Inuit languages - words to describe light snow, fluffy snow, wet snow - about the same number as in English. People will stick their finger into the wind on a chilly day and state with the confidence of a Met Office expert that `'it's too cold to snow''. Try telling that to people trapped in their Alaskan settlements in a blizzard at 40 degrees below. It is not true that snow cannot be eaten - it is pure water ice, and unless it fell from air contaminated by heavy industrial pollution, it would be completely harmless.

In our warm and soggy climate, snow is a rare and temporary nuisance. The sad white dusting which starts to melt as soon as it falls causes amusement for children and annoyance for the rail companies. But in a few places, determined by altitude and latitude, the snow does not all melt in summer. Over the centuries, it builds up, getting deeper and deeper, compacting under its own weight, changing from a soft fluffy mass, through a compact viscous interlocking of crystals with the density and consistency of the nastiest kind of snowball, eventually turning into clear blue ice. And still the snow falls, hundreds of feet up on the surface. Something has to give, and eventually, when the ice is thick enough and heavy enough, it starts to flow as a glacier. Like glass in a church window, which will sag under its own weight over the centuries, hard, clear glacier ice, as apparently solid as rock crystal, will, under extreme pressure, deform, buckle and slide downhill, forming a creeping, frozen river. If the ice build-up is great enough, a whole continent or mountain range can be covered in an ice cap. The ice sheets, of Greenland and Antarctica, continental in size, are thousands of metres thick and millions of years old. They act as huge heat sinks, chilling the seas around them, as they calve icebergs into the Arctic and Southern Oceans, reflecting the warmth of the sun back into space. They contain millions of cubic kilometres of fresh water, which if thawed, would slop into the world ocean, raising its level by the height of St Paul's Cathedral.

The Greenland ice sheet is vital to us: cold water sinking off its southern flank sucks warmer water in from the south to replace it. This is the engine that drives the currents that bring warm water, and warm winds, across the Atlantic. If this engine stalls, the British Isles would be plunged into a sub-polar climate commensurate with our latitude, the seas would freeze in winter, and southern England would have the climate of Newfoundland. We have good reasons to keep a wary eye on the ebb and flow of the ice world.

Snowflakes are a record of the air out of which they crystallised. The ice crystals that form in clouds are mostly empty space, and in the gaps between the clear dentritic branches, air molecules are trapped. Permanent ice provides scientists with a snapshot of the consistency and temperature of the air at the time. The beginning of the industrial revolution is recorded tens of metres down in the Greenland and Antarctic ice, marked by an increase in acidity and a steep rise in the amount of carbon dioxide, belched out by the smokestacks of the industrialising world and trapped in the compressed air bubbles of glacial ice. Changes in temperature, too, can be seen by drilling into the great glaciers. Oxygen, one of the constituents of water along with hydrogen, exists in different isotopes, given numbers denoting their atomic weight. Normal oxygen is called oxygen- 16, and forms more than 99 per cent of this vital atmospheric gas. Small amounts of other isotopes, notably oxygen-18, are also found. The proportion of oxygen-18 found bound up in the water molecules of the planet's icefields depends on the temperature at which the ice formed, and the amount of melting and refreezing that has occurred since. Isotopic analysis allows scientists to use ice as an amazingly accurate fossil thermometer, recording the temperature at the time the ice was deposited. As the greenhouse pessimists insist, the record for the last couple of centuries shows a definite warming, confirming their worst fears and direst predictions. However, the ice scientists have found that this warming has been seen before, thousands of years before the first automobile was built or the first power station was switched on.

Outside Greenland and Antarctica, the largest bodies of ice in the world are found in Iceland. The island lies in a climatic anomaly, as far north as the great Greenlandic ice sheet, but blessed, thanks to the warming current of the North Atlantic Drift with winter temperatures several degrees higher than anywhere this near to the pole has a right to have. Any change in the Earth's climate will therefore have a profound effect on Iceland's glaciers, delicately balanced on the thermal limits of existence. Even a slight warming could have a catastrophic effect of the ice caps, melting the millions of tonnes of ice, and washing away soil, roads and bridges in summer floods. If Iceland lost a significant part of its ice, this would, in itself, have little effect on the rest of the planet, but would act as a pointer of a catastrophe to come if the ice fields in the high Arctic and Antarctic were to follow. The popular consensus is that Iceland's reservoirs of cold are shrinking. Yet this is not happening. Between 1970 and 1994, the Icelandic glaciers were actually advancing. Since then, they have hovered, seemingly undecided whether to continue their march down to the plains or stay put. The Vikings who settled on the island 1,000 years ago told of a land covered in forests - forests that could never survive today. Our recent anecdotal evidence tell us that our climate is heating up - a decade of hot summers in Western Europe and the US have pushed global warming to the top of the agenda. But the scientific evidence is more confused.

Icelandic scientists have been involved in the project since the late 1980s to probe the ice sheet in nearby Greenland, drilling a hole through the ice cap thousands of metres down to the bedrock and studying the frozen record for clues about the climate in Earth's recent and not-so-recent past - the ice collected at the bottom fell as snow 200,000 years ago. Like the behaviour of the Icelandic glaciers, the evidence from Greenland is confusing. For the last 10,000 years, since the last major glaciation when Europe, northern Asia and most of North America were buried under ice, the climate in the North Atlantic has been remarkably stable. Scientists have always assumed that such climatic stability was typical of the relatively warm episodes between the glaciations of Earth's recent history. But when they had a look at the ice record from the time before the last ice age, around 100,000 years ago, they had a shock. Far from being an analogy to today's calm and stable world, this period, called the Eemian by geologists, was marked by violent and rapid temperature changes, not over the usual geological timescales of tens of thousands of years, but instead over centuries or even decades. `'Of course there were no cars then, no power stations, no industry. Yet there was rapid global warming and cooling. We simply do not understand the processes going on then that affected climate change. We don't really understand them now,'' says Thorstein Thorsteinsson, an Icelandic scientist working on the Greenland ice core project.

Indeed we don't. Even if carbon dioxide from our cars and power stations is warming the Earth, the result could be lots more ice and snow. Warmer air equals more evaporation from the oceans, which means more precipitation around the poles and on the high mountains, and this precipitation, even in a warmer world, will still fall as snow. As well as cooling the oceans by increased iceberg calving, more snow and ice in the far north and far south means more of the sun's heat is reflected into space, causing more cooling. Some doom-mongers have even postulated that man-made global warming could precipitate a new ice age in the 23rd century. Throw into this complex equation the huge, poorly understood ocean currents which play a vital part in determining climate on a global scale, the unpredictable effects of volcanic eruptions and changes in the sun itself, and it is clear why some developing nations are loath to accept as gospel the received wisdom that if they follow the West down the road to industrialisation - and prosperity - the result will be disaster.