Contemporary society's growing thirst for oil, coupled with the full development and exploitation of the more easily available sources of oil (such as Middle Eastern oil), mean that Western nations have been steadily pushing farther and farther into previously prohibitively hostile environments in the search for more oil supplies. These include the Canadian tarsands (once considered too complicated and expensive to develop for oil) and, of course, distant offshore locations. Arctic drilling represents one possible source of new oil which many hope to exploit in the near future, and which many also fear could result in unprecedented ecological catastrophes.
There is little doubt that the Arctic is a rich and untapped source of natural resources. Previously, the area went largely undeveloped, a combination of a prohibitive climate, great distance from industrial and population centres, and difficult local conditions (winter sea ice and permanent muskeg and permafrost on land, for instance, make any attempts at transportation complex, though not impossible). However, as more easily reached resource sites are tapped and as a gradual warming trend allows longer open-ice shipping seasons in the far north, Arctic natural resources are again coming under eager scrutiny. Arctic offshore drilling is, of course, one of the major effects. However, drilling on land in the Arctic is also being eagerly considered in, for example, the Arctic National Wildlife Refuge (which has been the site of major political controversies in recent years over whether drilling should be allowed).
Overall, the Arctic wildlife refuge is only one small part of the larger puzzle. Tens of billions of barrels of oil are believed to lie under the Arctic, but the area has only been partially explored. The Alaskan North Slope is one of the best-surveyed areas, and represents a rich source of oil which American governments have considered tapping for decades. (Whether tankers from the North Slope should be permitted to navigate what was then the only feasible waterway to southern markets, the North-West Passage through the Canadian Arctic, was a thorny international diplomatic issue during the 1970s for the Nixon, Ford, and Trudeau governments in those two countries.) As other sources of oil are fully exploited and gradually decline, the pressure to develop these Arctic oil sources in order to continue to feed our society's enormous appetite for oil is quickly becoming overwhelming.
Against this pressure stands, in essence: two arguments. The first is an inherently conservative one: drilling in the Arctic buys time (and therefore might be permitted), but essentially does nothing to solve the underlying problem. Sooner or later, humanity will run out of oil - and will face a painful transition to some alternative energy source. This will happen regardless of whether the Arctic is fully exploited for its oil, and therefore now is as good a time as any to begin seriously investing in alternative fuel sources.
The more strident and influential opposition to Arctic drilling, however, comes from those who fear its environmental consequences. The environmental consequences of the oil drilling itself, under normal circumstances, may be relatively marginal. Note that this may not be the case when, for example, pipelines or drilling projects interfere with the sensitive mating grounds used by massive Arctic caribou herds, which could face dramatic population declines in the face of development. This only points to a larger problem: the Arctic is an unusually sensitive and precarious environment, in which relatively few native species are able to eke out a borderline existence on what little comes available during the short growing season. Disruptions similar to those which occur farther south therefore would have proportionately much greater consequences in the Arctic.
Moreover, and even more seriously, there remains considerable uncertainty over what could actually be done in the event of a major disaster, such as an oil spill, in the high Arctic. The Exxon Valdez spill happened on the southern coast of Alaska, where mitigation efforts were easier, if still very difficult. Should a similar spill occur on the northern coast - or, worse, should an offshore project in the far north experience a similar fate to BP's spill in the Gulf of Mexico - it would be extremely difficult to reduce the environmental damages. Relief ships and crews would be much farther away, and most would lack the specialized technology necessary to operate for extended periods in the Arctic.
Even BP's efforts in the Gulf of Mexico, which are so far unsuccessful, and Exxon's at Prince William Sound, which were only partially effective in stemming the horrifying ecological consequences of the spill, probably could not even be attempted in the Arctic Ocean, or only following weeks or months of additional delays in moving equipment into position. One benefit is that the Arctic Ocean is generally much shallower. On the other hand, the last major offshore oil rig spill to require the drilling of a relief well, at Ixtoc, still required ten months of drilling despite being under just 160 feet of water. In the Arctic, there would be fewer ships on hand to assist, more inclement weather (although, thankfully, no risk of hurricanes), probably no chance at erecting more than a handful of booms, and a much more fragile environment at risk.
It is this dramatic threat to the environment, recently emphasized by the Gulf of Mexico oil spill, which remains the greatest reason not to allow oil drilling in the Arctic Ocean.