domingo, 29 de mayo de 2016

Agriculture and the air we breathe





Agricultural emissions are responsible for about half of all manmade pollution

—Catherine Elton

There’s much handwringing over the negative environmental effects of agriculture and livestock production. But one topic that is often absent from debates on how to sustainably feed the world is the role agriculture plays in air pollution. As it turns out, it plays a starring role. According to a study published recently in the journal Geophysical Research Letters, most of the air pollution over the western world is coming from agriculture.
“It was really a surprising finding,” says co-author Kostas Tsigaridis. “Agriculture is the primary contributor of aerosol air pollutants over extensive areas where millions of people live. I was expecting it would be industry or even residential sources.”
Ammonia emissions on farms come from livestock waste and nitrogen fertilizers. However, in order to form damaging aerosols, those emissions must combine with combustion emissions. So even if we don’t decrease agricultural ammonia emissions, but continue to reduce combustion emissions, air quality will improve.
The presence of these aerosols in the atmosphere have serious implications for human health. Inorganic aerosols, which are tiny particles suspended in gas, are the main component of manmade pollution with particulate matter smaller than 2.5 micrometers in diameter, known as PM2.5. Particulate matter causes lung cancer and cardiopulmonary deaths.
For the study, researchers used a NASA Earth system model with a module that tracks aerosols. This enabled them to use both climate and emissions data to calculate aerosol pollution around the world for a pre-industrial year (1850), current day (2010), and the future (2100). In addition to a base run, the researchers considered two additional scenarios, one in which all manmade emissions were set to zero, and one in which agricultural emissions were set to zero. This way, they could isolate three sources of pollution: natural, agricultural, and manmade without agriculture.
For the US, the researchers found that agricultural emissions are responsible for about half of all manmade pollution. In other words, food production, without even taking into account processing and transportation, is responsible for the same amount of PM2.5 as all other human activities combined. In Europe, it is responsible for 55 percent of all human activity-related air pollution.
On a positive note, the researchers found that by the end of the century, PM2.5 from manmade sources is set to decline—even though agricultural ammonia emissions could double by then. The reason for this apparently contradictory finding is that ammonia needs nitric oxide emissions to form aerosols, and these latter emissions are expected to decline in the US, Europe, and eastern China. The authors say that this means that increased food production shouldn’t affect air quality—if we can control combustion emissions.
Tsigaridis, an associate research scientist at Columbia University and NASA’s Goddard Institute for Space Studies warns, however, that this is no excuse to give livestock production and fertilizers a free pass. Both contribute to climate change, deforestation, and the pollution of our waterways, he says. “Air quality is only one piece of the puzzle.