Maritime Traffic Up Fourfold in Two Decades

Maritime traffic on the world’s oceans has increased 300 per cent over the past 20 years, according to a new study by the American Geophysical Union (AGU) aimed at quantifying global ship traffic.

The research used satellite data to estimate the number of vessels on the ocean every year between 1992 and 2012. The number of ships traversing the oceans grew by 60 percent between 1992 and 2002. Shipping traffic grew even faster during the second decade of the study, peaking at rate of increase of 10 percent per year in 2011.

Traffic went up in every ocean during the 20 years of the study, except off the coast of Somalia, where increasing piracy has almost completely halted commercial shipping since 2006. In the Indian Ocean, where the world’s busiest shipping lanes are located, ship traffic grew by more than 300 percent over the 20-year period, according to the research.

International trade and the sizes of merchant fleets have both enlarged rapidly over the past two decades, explaining the steep rise in ship traffic, the study reports. The new analysis has been accepted for publication in Geophysical Research Letters, a journal of the American Geophysical Union.

Jean Tournadre, a geophysicist at Ifremer, the French Institute for the Exploitation of the Sea in Plouzane, and the study author, said that ”ships powered by fossil fuels dump oil, fuel and waste into the water and pump exhaust into the air. Shipping is also a major source of noise pollution, which is increasingly considered potentially harmful to marine mammals.”

According to the study, burgeoning ship traffic has increased the amount of pollution in the atmosphere, particularly above the Sri Lanka-Sumatra-China shipping lane, where the study notes a 50 percent increase in nitrogen dioxide over the 20-year period.

Tournadre said he hopes the new study will increase scientists’ understanding of how human activities are affecting marine ecosystems and improve models of atmospheric pollution in the open ocean.

The new study is the first to track ship traffic on a global scale, Tournadre said. Currently, ship traffic is monitored using the Automatic Identification System (AIS). When vessels are near the coast, they use transponders to send out their location information to other ships and base stations on land. However, the AIS system doesn’t work very well when ships are out on the open ocean. Vessels are often out of range of terrestrial base stations or other ships, and few satellites carry the AIS instrumentation necessary to locate vessels from space.

The new method outlined in the study uses altimeters, or instruments that measure altitude, aboard satellites to detect the location of ships at sea, similar to the way these instruments have been used to track icebergs.

Tournadre found that the altimetry data accurately reproduced known shipping lanes and could be used to estimate the number of vessels on the ocean worldwide. The study used altimetry data from seven different satellites to map ship traffic from 1992 to 2012.

Using satellite data made it possible to calculate ship traffic for the entire globe, whereas AIS records provide relatively limited coverage in both space and time, Tournadre said. The new method also allowed him to look back at two decades of traffic using archived data, and give independent measurements of ship traffic that were not based on the will or capability of ships to transmit their own positions.

However, Tournadre also cautions that some of the growth he has seen in ship traffic could be overestimated because ships, especially container ships, have become larger over the past two decades and possibly easier to detect with altimetry data.

Press Release; Image: HHLA