Nitrous oxide, more harmful to the climate than CO2, increasing in atmosphere, study finds

A new study published in the journal Nature suggests that nitrous oxide a gas that is 300 times more harmful to the climate than carbon dioxide is steadily increasing in the atmosphere.

While nitrous oxide is produced in different ways, the study found the largest contributor is agriculture,where it is produced as a by-product of nitrogen, largely used in agriculture as a fertilizer.

The atmosphere's nitrous oxide had 270 parts per billion in 1750, according to the study, and had risen to 331 parts per billion in 2018. The fastest rise was in the last five decades.

The international team of authors say that, on the current trajectory, the additional nitrous oxide could push the global temperature to 3 C above the pre-industrial average by 2100, which is far past the target of 1.5 C or 2 C laid out by the Intergovernmental Panel on Climate Change (IPCC).

"Currently, the emissions are on the path to cause a global temperature increase above three degrees by the end of this century," said Hanqin Tian, co-lead author of the study and director of the International Center for Climate and Global Change Research at Auburn University's School of Forestry and Wildlife Sciences in Alabama.

"It highlights the urgency and it's critically important to think about this."

When it comes to climate change, three main greenhousegases are of particular concern: carbon dioxide (CO2), methane and nitrous oxide (N2O).

While most of the focus has been on CO2, there's beenrising concern about methane and N2O.

But nitrous oxide has largely been underestimated, according toanother of the study's authors.

"I don't think many people know about nitrous oxide, I would say, in terms of the magnitude of the emissions," said Parvadha Suntharalingamof the University of East Anglia's School of Environmental Sciences.

"On a sort of per molecule basis, oxide is more than 300 times as strong as a molecule of CO2 in terms of its global warming potential. So even though the magnitude of the emissions is less, the potency of the gas is much stronger. A little of it goes a long way."

"What's also been surprising is that we found that the emissions of nitrous oxide have been rising pretty sharply and much more sharply than [what was] predicted really in some of these emission scenarios developed for the IPCC."

The study found that agriculture was responsible for almost 70 per cent of the global human-causedN2O between 2007-16 with most coming from East Asia, Europe, South Asia and North America. But the highest growth rates were found in emerging economies like Brazil, India and China.

The authors suggest that with better farming practices, however, decreases could be significant, thus curbing the climb in N2O emissions.

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For example, they note Europe has seen a decline in N2O emissions due to the introduction of emissions trading and because of many countries moving to a more efficient use of fertilizer. The chemical industry also helped by reducing emissions.

Illimar Altosaar, a professor in the department of biochemistry, microbiology and immunology at the University of Ottawa who was not involved in the study, says it's a good study, but more needs to be investigated as to the role oceans play in emissions of N2O.

"The ocean is the key," he said. "We don't know the biochemistry [of the oceans]and it's the phytoplanktonand the blue green algae that are doing a lot of this gas exchange."

Suntharalingamsays another consideration that is still not well-known is how climate feedback affects N2O emissions such as increased precipitation caused by climate change affects moisture content in the soil, whichcan affect how much N2Ois generated.

The authors stress the importance of agriculture and believe that it just needs to change in some countries.

"You need fertilizer. You need the food industry, and you can't get away from the application of fertilizer," Suntharalingam said. "I think a takeaway is that managed fertilizer application can be very successful in reducing emissions and that Europe managed to reduce emissions but not depress food production.

"You just need to make sure that how much you apply when you apply it and how you apply it is carefully managed, and you can maintain crop yields, but you can definitely reduce the emissions from the soils. Managed fertilizer application is a very important mitigation strategy."