Pollution versus prosperity

As a science writer, I receive tens of press releases a day from journals, funding agencies, universities, and research institutes. Whether I open or delete an emailed release depends on its title. Among this week’s deletions were “NASA receives fourth consecutive clean audit opinion” and “Elsevier expands engineering content available on Knovel.”

But I opened “LHCb experiment observes two new baryon particles never seen before,” which I promptly posted on Physics Today‘s Facebook page , and “Worldwide ship traffic up 300 percent since 1992,” which so intrigued me that I’ve made it the subject of this blog post.

The ship-traffic release came from Kate Wheeling of the American Geophysical Union. The topic is a recent paper in Geophysical Research Letters by Jean Tournadre of the French Research Institute for Exploitation of the Sea.

Tournadre measured ship traffic by trawling through the databases of seven spacecraft whose radar altimeters mapped the height of Earth’s oceans from 1992 to 2012. Radar altimeters work by timing how long a pulsed signal takes to hit the sea surface and return to the spacecraft. They’re used to measure Earth’s changing sea level and investigate waves, among other things. As Tournadre has demonstrated, a spaceborne radar altimeter can also pinpoint the presence of a ship within an area of 35 km².

How long it takes a radar altimeter to map the entire ocean depends on its orbit. Three of the spacecraft in Tournadre’s study—TOPEX/Poseidon, Jason-1, and Jason-2—revisit a given patch of sea every 10 days. The newest spacecraft that he included, CryoSat, takes 369 days, because its orbit is optimized for studying Earth’s polar regions. Tournadre could not therefore track shipping on short time scales. Instead, he determined the annual density of ships.

The map above came from Wheeling’s press release, not Tournadre’s paper. It shows the world’s shipping lanes as they were in 2008. Tournadre determined how the use of those lanes has changed with time. He could see, for example, the impact on trade of Somali piracy, which has beset shipping around the Horn of Africa since 2005. He could also see a slight depression in worldwide shipping caused by the financial crisis of 2007–08.

But Tournadre’s biggest finding was the overall growth in shipping. As echoed in the press release that caught my eye, the world’s shipping has quadrupled in volume since 1992.

Tournadre chose to put a negative interpretation on his findings. “Ships,” he wrote, “are powered by fossil fuel creating the main source of air pollution in the open ocean.” They are also “one of the major sources of noise in the ocean with potential threat to marine animals that depend on sound for myriad ecological functions.” The bigger the volume of shipping is, the bigger the threat to marine ecosystems.

I don’t dispute Tournadre’s interpretation, but it should be considered alongside a positive one. When I first saw the map above, I marveled at what it implied: That Earth’s nations are buying and selling things among themselves. And thanks to Tournadre, we know that they’re doing so at an increasing rate.

Why is that increase good? According to an analysis by the CIA, world trade’s share of world GDP will rise from 20% in 1990 to a predicted 40% in 2015. In that same period, world GDP has doubled. The percentage of the world’s population living in extreme poverty in 1990 was 43%; in 2010, it was 21%.

Granted, a country’s economy can grow without trade, but it will grow more slowly. India’s growth rate took off in 1991 when its prime minister, Narasimha Rao, and finance minister (later, also prime minister*), Manmohan Singh, reduced the country’s formerly high tariffs and trade barriers.

There is, therefore, a tradeoff between pollution and prosperity. Thanks to Tournadre’s study, we have a better idea of what it is.

*Updated 25 November 2014: The original version of this post indicated that Manmohan Singh was the current president of India. That was incorrect. After serving as finance minister, Singh served as prime minister from 22 May 2004 to 26 May 2014.