When we think of the seas being polluted, what we tend to picture are oil spills. Even today, oil tankers are still responsible for an average of some twenty spills a year—and some of these have been so massive (exceeding 250,000 tons) that they have found their way into the history books. But pipelines, oil rigs, and refineries are by far the biggest source of oil spills, such spillages representing on average 5 times the volume of hydrocarbons spilled by tankers. The largest oil spill in history occurred in 1991, as a result of the Gulf War, and is said to have exceeded a million tons.
Oil spills, however, represent just a fraction of the harmful human waste that finds its way into the marine environment. A high proportion of all our waste products, from the most toxic to the most benign, end up in the ocean. This is firstly because rivers are mankind’s natural drains and rivers flow into the sea; and secondly because airborne pollutants have a high chance of being deposited in the world’s oceans, given their huge surface area. Coastal ecosystems are the most badly affected: agricultural pesticides and fertilizers, industrial waste, and domestic organic pollution flow into their waters faster and faster as coastal populations (already 40% of humanity) increase. But even the heart of the ocean is a rubbish dump: an estimated (but conservative) figure of 3 million tons of plastic is slowly revolving in the middle of the Pacific, covering an area the size of Texas.
There is no strictly maritime solution to the pollution of our seas. Certainly, regulations controlling the maritime transportation of harmful substances need to be tighter and, above all, to be better enforced. This was the stated objective of the international marine environmental convention known as Marpol (short for “marine pollution”), which has in fact succeeded in gradually reducing the number of serious accidents occurring at sea. The phasing out of the last single-hull tankers by 2015 is an initiative along similar lines. But the fundamental question relates to the waste itself: we need above all to reduce the amount produced, and we need to increase recycling. We also need to improve our systems for filtering fluvial and atmospheric waste and to make these more widespread, especially since we already have the necessary technology.