Mankind has continually abused the sea, regarding it as an inexhaustible source of food and minerals, and a dumping ground for rubbish. Now it is more widely accepted that the oceans are finite, and there is a need to use and manage them carefully, especially as globally environmental pressures are mounting because of the burgeoning human population. Pollution is important enough to be discussed separately.
Regarded by some people as a pollutant, this is a key substance in natural cycles and so cannot be treated like man-made substances. As a greenhouse gas, increasing concentrations of carbon dioxide in the atmosphere threaten climate change globally, modify ocean circulation, and so reduce the viability of many marine species. Sharp reductions in emissions per capita (>60%) are needed to avoid irreversible changes, bearing in mind the rate at which the human population is growing and future industrial expansion by the developing world, especially China. No one of the suite of solutions, which range from improving energy efficiency and switching to renewable energy sources, to capturing carbon dioxide and storing it somewhere—for instance, in deep geological deposits that formerly contained offshore oil and gas—is likely to be sufficient.
Over-exploitation of Living Resources.
This is now a growing and controversial problem. Fish, shellfish, and, in Asia, seaweeds are important sources of food, particularly in developing countries. Improvements in technology for locating and catching fish, and the considerable post-war expansion of commercial fisheries, resulted in fish catches peaking at over 100 million tonnes a year in 2000. But these catches are now declining, and the evidence is that the majority of fish stocks are either over-exploited, or close to being so. A seemingly logical solution is to develop farming techniques for fish and certain Crustacea, such as shrimps. However, these place a high demand on coastal areas and lead to habitat destruction and degradation, notably of the mangrove swamps in the Far East. Providing suitable feed for such farms is also a problem. A substantial proportion of the million tonnes of sand eels (Ammodytes sp.) caught by commercial fisheries in the North Sea gets used to feed not humans but poultry and farmed fishes.
Habitat Destruction and Alteration.
This is a major environmental issue in places. In the tropics the clearance of mangrove swamps not only destroys the nursery feeding grounds of many fishes, but also makes the coastline vulnerable to flooding and tsunami. In developed countries coastal defences, sea walls and groynes, alter coastal habitats and can result in coastal erosion elsewhere. Dredging shipping channels for deep-draught vessels like container ships and ro-ro ships, the building of port facilities, and removal of hazards to navigation, all lead to small pieces of habitat loss that globally lead to massive losses of coastal environments. The biggest problem is associated with the urbanization of the coastline. Most of the world's megalopolises (cities with more than 10 million people) are sited on coastlines and there is a general migration of people to coastal environments; over half of all people now live within 60 kilometres (37 mls.) of the sea, putting enormous environmental pressure on coastal habitats, with all the concomitant pollution problems.
Subjects: Maritime History.