When most people consider global warming, they often first think about carbon dioxide. After all, media coverage has emphasized climate change as an issue with human-induced causes; humans release large amounts of carbon into the atmosphere when burning fossil fuels for electricity, car fuel, etc.

However, a little-known fact is that much of climate change is actually related to natural causes. Assistant Professor at Emory University Dr. Eri Saikawa discussed this idea in her lecture entitled “Global and Regional Emissions Estimates for Nitrous Oxide (N2O): From Top-Down and Bottom-Up.”

Levels of N2O have been increasing at unsustainable rates. As a greenhouse gas, N2O molecules absorb longwave radiation from the Earth, containing radiation in the atmosphere and warming the planet’s overall temperature. Even more, N2O is the third largest greenhouse gas after carbon dioxide (CO2) and methane (CH4). N2O also has a long lifetime; its molecules remain in the atmosphere for roughly 114 years during which it can warm Earth, according to the Guardian.

On top of its role as a greenhouse gas, N2O is also an ozone-depleting substance. It breaks down the ozone layer, a layer of Earth’s atmosphere that partially protects Earth from the Sun’s radiation. As the ozone layer breaks down, more radiation reaches the Earth’s surface, warming the planet’s overall temperature.

So we know that the effects of N2O are threatening. But in order to stop these threats, what should we do? Where does N2O come from?

More than 50 percent of N2O emissions come from soil, and of this 50 percent, the majority of N20 emissions come from naturally-occurring soils rather than anthropogenic (human) soils used for agriculture, livestock, etc. N2O emissions can also come from natural cycling in Earth’s oceans.

Agriculture is responsible for the bulk of nitrous oxide emissions / Midwest 7-25-2011 008 / Richard Hurd / Creative Commons

Saikawa studied two research questions to better understand the causes of N2O emissions: What fraction of global N2O emissions comes from soil? And what quantity of emissions do we see from various regions?

The studies ultimately found that there is a decrease in natural soil N2O emissions during El Niño years, or years characterized by unusually warm ocean temperatures and increased precipitation in areas around the equator in the Pacific Ocean. Additionally, there are increasing N2O emissions from China and India. However, emissions are also released globally and throughout all times of the year.

It’s important to understand the role of N2O in climate change and to take appropriate actions to limit its effects. Thus far, N2O is not included in the Montreal Protocol, an international treaty designed to gradually lessen the number of existence of substances that deplete the ozone layer in the atmosphere. As a result, people generally pay less attention to it as a potential threat, so emissions are continuing to significantly increase.

With Saikawa’s studies, we can better understand the sources of N2O emissions, which can ultimately help us to find the right solutions.

This podcast by Richard Harris for NPR further explains the role of N2O in agricultural emissions:

Read more about ozone depletion here.


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