sounds just like the Arctic ice. Its snow- and ice-melt gave rise to the frost giant Ymir, from whose body the whole cosmos was formed. Today, science tells us a different story about the sea ice, but in that story, too, the ice is far older than humans. According to Polyak et al. (2010):
…sea ice became a feature of the Arctic by 47 [million years before the present], following a pronounced decline [in carbon dioxide concentrations]… Ice was apparently most widespread during the last 2–3 million years, in accordance with Earth's overall cooler climate.
Since modern humans are just 200,000 years old, the ice might as well be eternal.
But not unchanging. We live in that part of an ice age that is termed an interglacial, when some of the ice retreats in summer. During modern human history the ice cap has melted back each summer as Earth tipped toward the sun, then grown again with new freezing as the year turned toward the Winter solstice.
Polyak et al. continues:
Nevertheless, episodes of considerably reduced sea ice or even seasonally ice-free conditions occurred... The current reduction in Arctic ice cover started in the late 19th century, consistent with the rapidly warming climate, and became very pronounced over the last three decades. This ice loss appears to be unmatched over at least the last few thousand years…
This information is based upon the detailed study of ‘proxies’—indirect indicators of sea ice extent, including sea-floor sediments containing distinctive mineral, chemical and biological markers; coastal records which include things as diverse as ancient driftwood and geological beach formations; ice-cores from nearby land ice; and tree-ring records, where available.
Direct observations of sea ice go back a surprisingly long way: a Greek navigator, Pytheas of Massilia, sailed into the open Atlantic in 325 BCE, reaching:
…a land he called "Eschate Thule," where the Sun only set for three hours each day and the water was replaced by a congealed substance "on which one can neither walk nor sail." He was probably describing loose sea ice known today as "growlers," or "bergy bits." His "Thule" was probably Norway…
Since then, humans have repeatedly encountered the ice, from 11th century Novaya Zemlya, to the Norse colony in Medieval Greenland, to Henry Larsen’s 1944 transit of the Northwest Passage. For many it proved a fatal encounter; the names of Hugh Willoughby, Willem Barents, Henry Hudson, and John Franklin would only begin a list of Arctic explorers who bartered their lives for their discoveries. During this time, the annual melt and refreeze of the ice has been relatively consistent.
But that has changed. Since the turn of the millennium, transits of Northwest and Northeast Passages have increased dramatically. In the Northeast, millions of tons of supertanker traffic have passed already, and Russian infrastructure investments indicate that this is a mere beginning. In the Northwest, Arctic charter cruising has become a growing industry. In both, recreational boaters are increasingly common; and many of them now report that they see no pack ice at all.
Science confirms this anecdotal evidence: satellite measurements show that the ice extent has shrunk since 1979 by nearly 30%. More alarming still, the estimated volume of the sea ice is down a whopping 75%! When the IPCC released its Fourth Assessment Report in 2007, it was generally thought that the Arctic could become ice-free somewhere near the end of this century. But ice loss has progressed at such speed that scientists now think 2030 might bring the first ice-free Arctic summer. Some say it could even happen this decade.
And if it does? Well, the Arctic sea ice is a highly efficient reflector of solar energy; where there is no ice, dark ocean water absorbs most of the sunlight. The less ice there is, then, the more the ocean heats up. This in turn melts more ice—an example of a positive feedback in action. It is a feedback chain bearing all kinds of consequences for the Arctic region. Disappearing ice can be good for some species; for instance, tiny algae may profit from the warmer waters and an extended growing season. But those species dependent upon the sea ice for sustenance or habitat—species from microscopic sea ice diatoms, to seals and walrus, to those charismatic polar bears—may suffer, perhaps even to the point of catastrophe.
Rapidly changing conditions also have repercussions for human populations, whose income and culture depend on sea ice. Their communities literally melt and wash awaywith no sea ice to weaken wave action, and their food supplies—often still 50% ‘country food’—are at risk, as populations of traditional prey species (and frequently access to themas well) are disrupted.
But what happens in the Arctic doesn't stay in the Arctic. When sea ice cover disappears, the changing interaction between sea and atmosphere can shift atmospheric patterns. The results may be felt all over the Northern Hemisphere. As we have seen, a smaller ice pack, combined with an ever earlier melting season, means more and more sunlight is soaked up by dark ocean waters. These warmer waters then release heat and moisture to the atmosphere during fall and winter—an effect already being observed and measured.
This change in turn may already be disturbing the jet stream, the high-altitude wind that separates southern warm air from cold Polar air. A destabilized jet stream becomes more 'wavy,' allowing frigid air to plunge farther south, a possible factor in the extreme winters that were experienced all around the Northern Hemisphere in recent years.
Another side-effect is that as the jet stream waves become larger, they slow down or even stall at times, leading to a significant increase in so-called blocking events. These cause extreme weather simply because they lead to unusually prolonged conditions of one type or another. The recent prolonged heatwave, drought and wildfires in the USA are one example of what can happen; another is the cool, dull and extremely wet first half of summer 2012 in the UK and other parts of Eurasia.
The accumulation of heat in Arctic waters also influences other frozen parts of the Arctic, such as glaciers and ice caps on Greenland and in the Canadian Archipelago. As there is less and less sea ice to act as a buffer, more energy can go into both melting glaciers from below, and warming the air above them. This has a marked effect on Greenland's marine-terminating glaciers and the Greenland Ice Sheet. Not only are glaciers flowing faster towards sea, but there is also a rapid increase in the summer surface melt Greenland experiences, leading to accelerating mass loss from the Greenland Ice Sheet. As the Arctic warms, an increased contribution to sea level rise is inevitable.
Another way Arctic warming could have worldwide consequences is through its influence on permafrost. Permanently frozen soils worldwide contain 1,400–1,700 Gigatons of carbon, about four times more than all the carbon emitted by human activity in modern times. A 2008 study found that a period of abrupt sea-ice loss could lead to rapid soil thaw, as far as 900 miles inland. Apart from widespread damage to infrastructure in northern territories (such as roads, houses and pipelines), the resulting annual carbon emissions could eventually amount to 15–35% of today’s yearly emissions from human activities. This would make the reduction of atmospheric greenhouse gases a much more difficult task.
An even more worrying potential source of greenhouse gases is the methane in the seabed of the Arctic Ocean, notably off the coast of Siberia. These so-called clathrates contain an estimated 1,400 gigatons of methane, a more potent though shorter-lived greenhouse gas than carbon dioxide. Methane clathrate, a form of water ice that contains a large amount of methane within its crystal structure, remains stable under a combination of high pressure and low temperature.
At a depth of 50 meters or less, the East Siberian Arctic Shelf may contain the shallowest methane clathrate deposits, and thus those most vulnerable to rising water temperatures. High amounts of methane have been recently been measured over ice-free portions of the Arctic Ocean, and the waters of the East Siberian Sea have been shown to be “super-saturated” with methane; large plumes of methane bubbles have been observed there as well. The origins and significance of these emissions are not yet clear, but Arctic methane emissions in general appear to be rising: methane concentrations in the Arctic now average about 1.90 parts per million, the highest in 400,000 years.
Apart from these unrecoverable sources of fossil fuel, the Arctic is also endowed with large amounts of recoverable oil and natural gas. As the sea ice retreats, the Arctic's fossil treasures are eyed greedily by large corporations and nations bordering the Arctic Ocean. This might lead to geopolitical tensions in a world where energy is rapidly becoming more expensive. (It is also highly ironic that the most likely cause of the disappearance of Arctic sea ice — the extraction and burning of fossil fuels — could lead to more extraction of said fuels. Another feedback loop.)
News articles on the dangers of Arctic sea ice loss are usually illustrated with pictures of polar bears. But although many animals in the Arctic are threatened by the vanishing Arctic sea ice, homo sapiens may be the species with most at stake. While Arctic sea ice may be “out of sight, out of mind” for many, it does affect human civilization over the Northern hemisphere, and even beyond: after thousands of years in which the sea ice played a vital role in the relatively stable conditions under which modern civilization, agriculture and a 7 billion strong world population could develop, it increasingly looks as if warming caused by the emission of greenhouse gases is bringing these stable conditions to an end.
Whether there still is time to save the Arctic sea ice is difficult to tell, but as we've seen, serious consequences will flow from the disappearance of the sea ice. It appears that these consequences can only be mitigated by keeping fossil fuels in the ground, and carbon out of the air. Whichever way you look at it, business-as-usual is not a sane option.
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