Shipping Traffic Increases Fourfold Leading to Pollution Concerns
Global ship traffic has exploded during the past two decades, likely bringing with it more air, water and even noise pollution, according to a new study by the American Geophysical Union.
Using satellite data to estimate oceangoing transport, the Union estimated that the number of ships on the seas increased in every year covered by the study, from 1992 through 2012. It jumped by 60% between 1992 and 2002, then accelerated in the subsequent decade, reaching a peak of 10% annual growth in 2011, the study found. Total growth over the 20-year period was fourfold.
This growth in shipping occurred in every ocean throughout these 20 years except in waters off Somalia, where commercial shipping has come to a virtual halt since 2006 because of rampant piracy. The adjacent Indian Ocean, though, is the busiest area for maritime shipping, and there traffic grew by more than 300% during the study period.
Jean Tournadre, the study’s author and a geophysicist at Ifremer said, “I found it quite worrisome that the ship traffic grew so much, even in very remote regions of the world, especially when we know that [ships] are the major source of pollution [on the open ocean].”
Tournadre said vessels powered by conventional fuels not only emit exhaust into the sea air, but also dump oil, fuel and waste into the water. And the noise of modern tankers and other commercial vessels is believed to be harmful to many species of marine mammals.
The increase in maritime shipping has matched the rise in international trade in the past 20 years, and that has led to a parallel growth in the sizes of merchant fleets, according to the study, published November 17 in the journal Geophysical Research Letters.
Of particular concern is atmospheric pollution over the busy shipping lane linking Sri Lanka, Sumatra and China, stretching from the Indian Ocean to the South and East China seas. The study found that concentrations of the pollutant nitrogen dioxide rose by 50% during the study period.
Tournadre said his study is the first to monitor maritime traffic worldwide with such accuracy. Until now, ship movements have been tracked using what’s known as the Automatic Identification System (AIS). This involves ships using transponders to communicate their locations to other ships as well as to shore-based tracking stations.
This system isn’t much help, however, when ships are on the open sea with no other vessels nearby and land-based stations are hundreds of miles away. Also, few satellites are equipped with AIS equipment to track ships from space.
So in his study, Tournadre used seven satellites equipped with altimeters – instruments that measure altitude – to detect the locations of ships, just as they track icebergs that can threaten shipping. Each altimeter bounced a radar pulse off the sea, then measured how long the pulse took to return to the satellite.
That measurement included information to construct an image of what was on the water’s surface, allowing monitors to determine whether it was a small island, an iceberg or a ship.
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