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| Earth on Apr 08, 2012

Fertilizers linked to increasing nitrous oxide in atmosphere

The rise in atmospheric nitrous oxide – a greenhouse gas – is largely the result of the use of nitrogen-based fertilizers, according to Berkeley chemists.

University of California, Berkeley, chemists said in early April 2012 that the increased use of nitrogen-based fertilizers has caused a dramatic rise in atmospheric nitrous oxide, which is a major greenhouse gas contributing to global climate change.

According to these scientists, other studies have revealed that nitrous oxide levels have risen 20 percent since 1750 – from below 270 parts per billion (ppb) to more than 320 ppb. Their study tracks nitrous oxide increases from more recent decades, since 1940. The scientists say that, after carbon dioxide and methane, nitrous oxide is the most potent greenhouse gas. Like carbon dioxide, it traps heat and contributes to the ongoing global warming observed by scientists.

In addition, atmospheric nitrous oxide destroys stratospheric ozone, which protects the planet from harmful ultraviolet rays from the sun.

The Berkeley scientists analyzed air samples going back to 1978 from the Cape Grim Baseline Air Pollution Station in Tasmania. The samples help confirm that nitrogen-based fertilizer is largely responsible for the 20 percent increase in atmospheric nitrous oxide since the Industrial Revolution. Photo courtesy of CSIRO.

The new study, reported in the April 2012 issue of the journal Nature Geoscience, involved analyzing nitrogen isotope data in archived air samples from Antarctica and Tasmania to identify the chemical fingerprint related to fertilizer use. Long-term trends observed in the data allowed the scientists to “distinguish between natural and anthropogenic sources of nitrous oxide,” they said. They said their study confirmed that:

… the rise in atmospheric nitrous oxide levels is largely the result of an increased reliance on nitrogen-based fertilizers.

Study leader Kristie Boering, a UC Berkeley professor of chemistry and of Earth and planetary science, was quick to point out that her science team is not “vilifying” fertilizer. After all, the rise in the use of inexpensive, synthetic fertilizers helped fuel the so-called green revolution that began in the 1960s, during which food production for Earth’s burgeoning human population also increased dramatically (from 3 billion humans in the 1960s to over 7 billion today). Boering said in a press release:

We are not vilifying fertilizer. We can’t just stop using fertilizer. But we hope this study will contribute to changes in fertilizer use and agricultural practices that will help to mitigate the release of nitrous oxide into the atmosphere.

Fertilizer use helped fuel the revolution in agriculture since the 1960s that has helped feed Earth's growing population. These scientists say they hope their study will help farmers determine which fertilization strategies are most effective. Image via HighTechLandscapes.com

Boering and her colleagues obtained air samples from Antarctic ice, called firn air, dating from 1940 to 2005, and from an atmospheric monitoring station at Cape Grim, Tasmania, which has archived air back to 1978.

Boering’s team hopes their study will help farmers determine which fertilization strategies are most effective.

Bottom line: Analysis of air samples dating back to 1940s from Antarctica, and to 1978 from Tasmania, indicate that the increased use of nitrogen-based fertilizers has caused a dramatic rise in atmospheric nitrous oxide a major greenhouse gas, said University of California Berkeley chemists said in an April 2012 report in Nature Geoscience.

Read more from Berkeley News Center