Melting glaciers

As recently as 1981 the maverick astronomer Sir Fred Hoyle published a book called Ice: The Ultimate Human Catastrophe predicting a new ice age. One possibility he considered was that an ice age might be triggered by a large meteorite impact putting enough dust into the Earths atmosphere to cause significant cooling. At the time Hoyle wrote Ice, there was also an increasing awareness that the use of nuclear weapons could have the same effect: they might start fires that would cool the Earth by putting large amounts of smoke and dust into the atmosphere, a scenario called nuclear winter. Hoyle added that a giant volcano or an asteroid impact could have the same effect. He thought this might happen within a decade. However, only a couple of decades on from the books publication the current fear is quite the opposite – that the Earth may be heating up. What does this mean for the icy regions of the Earth?

Tales of retreating glaciers have been increasingly in the news in recent years, either because glaciers are retreating more or because the media have caught on to the idea – or both, this authors favoured explanation. The term that the glaciologists like to use is “mass balance”, the gain or loss of ice from a glacier. The story is by no means simple. The glacier cover of the Alps may have diminished by up to 40 percent in area since 1850, or 50 percent in terms of mass. But in Scandinavia – mainly Norway – there seems to be more ice rather than less in the biggest glaciers.

However, the total equation since 1960 seems to suggest a mass balance 6000 cubic kilometres in debit across the glaciers for which there are sensible data, including those in most of the major mountain regions of the northern hemisphere. It is not likely that these are a statistically unrepresentative sample.

Some of this change is probably natural. As we have seen, we are living in an interglacial. The glaciers will probably go on retreating until they start to grow again as the next ice age sets in. But there are estimates that another 16cm of sea level rise could be caused by glacier melting during this century.

Glacier surges

The great glaciers of Alaska and northern Canada have been observed displaying “surges” in which they advance by many tens of metres a year. But this is not a sign of expansion. It often happens because they are being undercut by streams formed as they melt, which lubricate their progress and hasten yet more melting. An example is the Bering Glacier, the biggest in North America. It surged and then retreated several times during the twentieth century and lost 130 of its 5200 square kilometres of area.

Between 1993 and 1995 the glacier moved forward by about 5km and satellite positioning has been used to measure the thinning of the ice further up the glacier as it moves downwards or melts. Seafarers might rejoice at losing this and other “maritime” glaciers, those that end in the sea. They are the prime source of icebergs in the oceans further south. But the local environmental effects are far less welcome.

There appear to be several ways in which glaciers surge. Tavi Murray of Leeds University in the UK says that some surges are long and slow, lasting over a decade and occurring at a pace of “only” 2-5m a day. They happen when water saturates the soil beneath a glacier and its grip on the ground below is weakened. The other type of surge lasts a year or two but can involve movement of up to 50m a day. This happens when the normal water flow beneath a glacier is diverted into cavities in the ice and large amounts of pressure build up.

Roof of the world

People who worry about climate change tend to talk about what would happen it the Antarctic ice sheet or the glaciers of Greenland melt. And as we have seen, these ice masses are so huge that their melting would mean major environmental damage via sea level rise and other effects. By contrast, the rest of the worlds glaciers contain less water and their disappearance would be a regional rather than a global disaster.

It the Earth is losing its glaciers, the place where it matters most is in the Himalayas. The Himalayas are a mountain chain 2500km long, with innumerable subsidiary chains such as the Hindu Kush. They contain the worlds highest mountains including all fourteen that are more than 8000m high. The area contains an estimated 67 peaks higher than Aconcagua in the Andes, at 6960m the highest mountain not in the Himalayan region.

As well as being a stupendous mountain system in their own right, the Himalayas are backed by the Tibetan plateau, one of the worlds biggest upland regions. Most of it lies about 4000m above sea level. A new Chinese state atlas of the country's icy, desert and tundra regions claimed in 2005 that China had nearly 60,000 square kilometres of glacier. Most of this is in the politically disputed area of Tibet – or “the country's west”, as the state news agency euphemistically puts it.

Their height and size mean that the Himalayas help shape the Earths climate, as we saw in Chapter 5. And just as the Andes and the mountains of East Africa give the world the Amazon and the Nile, the Himalayas are the source of some of the world's great rivers, including the Indus, the Ganges, the Yangtze, the Mekong and the Brahmaputra.

Immense glaciers surround all the major Himalayan peaks. As with other glaciers in the world, they are a navigational hazard to climbers because the ice is not solid and forms crevasses that can trap the unwary. Crossing them is a major part of Himalayan climbing, as the many accounts of crossing the Icefall, the glacier on the main route up Everest, suggest.

It is not likely that this much ice is going to vanish in the next few decades. But there is every chance that these glaciers will go on shrinking at a far faster pace than they have in recent centuries.

These changes would reflect big alterations in the environment at high altitude. Small glaciers would vanish and big ones would retreat. There are signs that this is already happening. In the Garhwal Himalaya, the Gangotri Glacier has been retreating since 1780, but the process has sped up since 1971. It has lost 850m of its original 31km length since then.

On the Tibetan plateau, the Meili Glacier has retreated by about 20-30m a year since 1998. In 2003, scientists calculated that the average temperature in the area had risen by only about 1°C over thirty years, not much by the standards of global warming. This may suggest that other forces are at work. But they add that there is a possible mechanism for the change. If water that once fell as snow now lands as rain, it will erode the ice instead of adding to it. The same story applies to many other of the 46,298 glaciers said to be on the plateau. According to Japans Asahi newspaper, the volume of water coming off them has increased by 20 percent over the last 40 years and their area has dwindled by 7 percent.

Snow at the Equator?

Glacier retreat is also going on in more unexpected parts of the world. Nobody believed the eighteenth-century European travellers who first reported snow at the Equator in Africa. They may have been wrong about the dragons and the unicorns, but on this at least they were right. Mount Kenya is on the Equator and has permanent snow.

The snow stays there for a number of reasons. One is that the snow-fields are high, with the summit of Mount Kenya 5199m above sea level. More importantly, snow is white. So it reflects away most of the incoming solar energy and stays frozen.

It is not only visitors from cooler parts of the world who are fascinated by these large areas of the icy Earth near the Equator. People living near Mount Kenya, Kirinyaga in local languages, have long had legends in which it plays a role as heaven for the dead. More in line with current science, the same people recognized its importance in creating the local weather.

In the modern era, we have come to realize that the big snow and ice zones we see today in the uplands of Kenya and Tanzania are only the fossil remains of expanses that were once much larger. Although he seems never to have visited Africa, Agassiz would have found all the signs of an ancient ice age in abundance in East Africa, the Atlas mountains of north-west Africa, and southern Africa, although here the remains are of older ice ages. Nor is snow at the Equator confined to Africa. In 1632, the Dutch sea captain Jan Carstensz sighted more of the stuff just south of the line on Irian Jaya, the easternmost part of what is now Indonesia. The peak he saw is still called the Carstensz Pyramid, 4884m high. And of course, the Equator also passes through the Andes, the planets most prominent mountain range after the Himalayas.

Although the persistence of ice in these areas is striking, it should not be taken for granted. Scientists looking at Mount Kenya report that the mountain and its surroundings have a dozen glaciers left, but they are all retreating fast and others have already gone. The mountain was once well over 6000m high, before severe glacial erosion took over 1000m off it. Some time soon, the glaciers that did this could be gone. Kilimanjaro in Tanzania, Africa's highest peak at 5895m, is reported to have lost 80 percent of its glaciers in the last century. The same story could be told from Norway to Argentina. It ice fields do vanish, other things change too.

Many of these environments have Alpine-related ecology containing species that are unknown elsewhere. Perhaps more importantly, the Nile, the world's longest and possibly most important river, is fed by lakes that themselves are filled by water from the great mountains of East Africa. As we saw, the Nile's water is already in too much demand for its supply to be endangered.