When it comes to climate change issues, the spotlight is always on the regulation of carbon dioxide emissions from fossil fuels. However, just focusing on CO2 means overlooking other aspects that drive the rise of global temperatures, a new study revealed.

This includes aspects of the terrestrial biosphere: global food production, rice cultivation, and animal farming, as well as waste disposal. Such activities produce two other main greenhouse gases: methane and nitrous oxide.

Our Terrestrial Biosphere

In 2014, a study revealed that although increased farming provides us food, it is also responsible for climate change.

Now, a new study, which is featured in the journal Nature, points to global agriculture as another culprit that contributes to climate change in the same way that fossil fuels do.

Every year, our terrestrial biosphere -- the surface where land animals, plants and microorganisms dwell -- absorbs about a quarter of the total CO2 emissions that humans produce. This helps moderate global temperatures.

Humans produce a whopping 40 billion tons of CO2 emissions annually, which comes from deforestation and the burning of fossil fuels. This has contributed to the 82 percent rise in warming due to greenhouse gases over the past decade.

But there are other greenhouse gases that are more abundant than CO2. According to lead study author Hanqin Tian of Auburn University, the potential of global warming due to methane is 28 times higher than than of CO2. Additionally, a nitrous oxide global warming is 265 times more likely than CO2 in the course of a century.

"These two gases are really important non-CO2 greenhouse gases," said Tian.

Methane not only emerges from oil leaks and gas operations, it is also released by ruminants, landfills and wetlands.

On the other hand, nitrous oxide comes from nitrogen fertilizers used in agriculture. Only 17 out of 100 units of nitrogen applied to the crop system ends up in the food we eat, Business Insider reported.

Sink Versus Source

Tian and his colleagues calculated how much nitrous oxide, methane and CO2 the terrestrial biosphere is absorbing each year versus how much it is releasing.

If the land absorbs more than it produces, it is called a "sink." But if it produces more than it absorbs, it's already a "source."

Researchers found that although terrestrial living things absorb more CO2 every year than what they are producing, they are still a net source of nitrous oxide and methane.

When the three gases are converted into a comparable unit based on their potential to warm Earth over a century, the biosphere becomes a source of greenhouse gases. It would cause a warming equal to about 3.8 or 5.4 billion tons CO2 emissions every year.

"Human actions not only are emitting greenhouse gases based on our own activities, but also are causing plants and animals and microbes to be net emitters of greenhouse gases as well," said study co-author Anna Michalak.

And so, the findings of their study overturns assumptions that the Earth is a sink, especially because those studies did not take into account methane and nitrous oxide, researchers said.

Scientists call on the public to direct attention to the role of the food system in climate mitigation. Countries have shown little interest on the matter because one thing is at stake: feeding the people.

Pep Canadell from CSIRO told ABC News that we need to re-think the ways to feed the population, especially a population interested in meat-rich diets.

"We really need to look at completely different ways to become much more efficient," said Canadell.

This would involve sustainable intensification of lands that would minimize the overall impact of other greenhouse gases such as nitrous oxide and methane, he added.

Photo: John Morton | Flickr 

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