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.
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. 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.
