Study Finds Surprising Byproduct of Middle Eastern Conflicts: Cleaner Air

Civil unrest and humanitarian crises can now be detected from space — because of, somewhat surprisingly, cleaner air.

A paper published on Friday in the journal Science analyzed satellite data from observations of major cities in the Middle East and found that measurements of nitrogen oxides in the air around those cities provided insights into the effects of war, civil unrest and other crises.

Nitrogen dioxide, a byproduct of the burning of fossil fuels, is part of the chemical reactions that produce ozone and smog. Nitrogen oxides are often used by scientists as an indicator of economic activity and of the effectiveness of pollution-control measures.

From 2005 to 2010, the Middle East had some of the world’s fastest-growing levels of polluting emissions, in step with economic development. According to the paper, however, in recent years many of the cities in the region showed a rapid decline in levels of nitrogen oxides, while levels continued to rise elsewhere in the world.

That insight may not seem surprising, given war’s dampening effects on economic activity. But the research employed a new tool for recognizing the effects.

Jos Lelieveld, the lead author of the study and a researcher at the Max Planck Institute for Chemistry in Mainz, Germany, said that by using tools aboard the NASA satellite Aura, he and his colleagues found decreasing levels of pollutants that corresponded to geopolitical crises that included armed conflict, trade sanctions and the rise of the Islamic State. “Each of these countries has an individual story,” he said.

International sanctions against Iran, he noted, caused an economic downturn that correlated with a steep drop in the pollutants after 2010. Nitrogen dioxide levels rose in Iraq after the war but have decreased sharply around the cities of Baghdad, Samarra and Tikrit with the rise of the Islamic State and its effect on the regional economy.

Uprisings in Syria could be tied to lower nitrogen dioxide levels over cities like Damascus and Aleppo; the Lebanese cities Beirut and Tripoli experienced increases in nitrogen dioxide levels that correlated with an influx of Syrians fleeing unrest. Public turmoil in Egypt can be associated with its strong decline in air pollution since 2011, he said.

Increasingly, scientists and national security experts have examined the effects of the environment on geopolitical conflict. A study released this year argued that an extreme drought in Syria between 2006 and 2009 was most likely made worse by climate change. It went on to note that the drought was a factor in the violent uprising and the rise of the Islamic State, which began ravaging that country in 2011. (Last month, the Republican Party chairman Reince Priebus ridiculed the presidential candidate Martin O’Malley for discussing that possible connection.)

The new research suggests that effects also flow in the opposite direction and shows ways in which the environment is affected by geopolitics. “It is tragic that some of the observed recent negative NO₂ trends are associated with humanitarian catastrophes,” the paper concludes.

The space-based observations can be used as a “thermometer” of crises, Dr. Lelieveld said, and could even serve as a new way to measure the effectiveness of sanctions. “I don’t think it was ever before possible,” he said, “to observe something like that from space.”

The new research received a cautious endorsement from Gavin Schmidt, head of the Goddard Institute for Space Studies, a part of NASA that studies climate change. “These attributions are very suggestive and deserve further study,” he said, but he noted that proving a link between world events and satellite measurements would require an in-depth analysis with plentiful data from measurements on the ground as well as extensive analysis to account for factors like weather.

Steven Cohen, executive director of the Earth Institute at Columbia University, warned against seeing the decline in some pollutants as any kind of positive sign. “War is always an ecological catastrophe,” he said. Even if some air pollutants are reduced as economic activities decline, he added, dangerous chemicals in the land and water “are likely on the rise due to the use of modern weapons of war.”

Dr. Lelieveld agreed. The fact that air seems to clear up during conflicts was hardly good news, he said. “This is not the ‘silver lining of war,’ ” he said. “It’s just an indicator of what’s going on.”