From a purely territorial perspective, these are bullish times for the world's oceans. As anthropogenic climate change picks up pace, seas around the world are rising, due to thermal expansion and the melting of alpine glaciers and arctic ice sheets; according to most scientists, by at least a meter by the year 2100. As a result, low-lying coastal areas around the world, and in several cases entire island nations, are expected to be reclaimed by the sea. Global sea level rise complicates the resolution of questions that have presented geopolitical difficulties for centuries: who owns the sea, and how much of it do they own? According to the UN Convention on the Law of the Sea (UNCLOS), concluded in 1982, countries have exclusive control over their seabed materials out to the extent of their continental shelf (but with a minimum of 200, and maximum of 350, Nautical miles from their coastline). In addition, they have broader control over marine resources (including, crucially, fishing stocks) in an Exclusive Economic Zone (EEZ) extending 200 nautical miles from the low-water mark on their coastlines.
As coastlines recede, current definitions (as discussed above) mandate that EEZs should also recede. This is an unpopular result, however, and so in response leading academics have called for all baselines to be fixed at "natural" (pre-sea level rise) levels. The easiest way to achieve this, of course, would be to amend UNCLOS directly to redefine the geographical boundaries of EEZs. However, given past difficulties in reaching consensus and several countries' (notably the United States') refusal to sign UNCLOS, this may not be a viable long-term strategy. Instead, individual nations should resolve such issues bilaterally (by making agreements with their neighbors not to contest existing boundaries), or unilaterally (by domestically redefining their own coastal boundaries). The latter option is particularly promising: as Rosemary Rayfuse outlined at the Threatened Island Nations Conference, hosted in May 2011 at Columbia University, states can avoid definitional difficulties related to the low-water mark by simply defining their low water mark as straight lines between geographic points. This more abstract definition would be less susceptible to physical alterations.
Such definitions still may be not enough for states whose entire territory is threatened, however. Both customary international law and UNCLOS limit marine territories to bona fide states; and so central to the maintenance of any zone for countries facing complete inundation of their territories will be a continued diplomatic push to maintain statehood even if they are forced to abandon their ancestral homes.
Sea level rise presents several other difficulties, especially to coastal ecosystems and infrastructure, which merit serious attention. Many of these impacts are likely to be most felt by the developing world, and by small island nations, some of whose entire territory lies just a few meters above current median sea levels. The Columbia conference addressed several of these questions with particular emphasis on the Republic of the Marshall Islands, a small developing country sitting no more than five meters above the sea today. Also, all is not well in the oceans themselves; although they look set to expand their reach, they are also heating up and, from interactions with higher carbon dioxide concentrations, becoming more acidic. As a result, marine ecosystems are changing, and most notably coral reefs are in grave danger.
Oceans are clearly gaining on the geographic front however, and their gain is mankind's loss. As a civilization our laws are often based on the assumption of a static world. This norm is now being challenged, as global climate change shifts natural boundaries. The definition of marine territories is just one area where old laws may lead to difficulties in the changing future; but it is one that nations hoping to maintain existing rights should address as soon as possible.