While climate change discussions focus largely on carbon dioxide, emissions of the third-most important greenhouse gas is rising dramatically in China. And not only does this gas, nitrous oxide (N2O), contribute to the greenhouse effect, but it also threatens to eat away at the ozone layer, which protects us by absorbing some of the ultraviolet light from the sun. Concerned about the double threat of N2O, researchers from Peking University took a closer look at its historical and future emissions. Here are the highlights of a Q&A with Jianhua Xu on what his team found and what it means for the planet.
Q. What’s the most important finding from your study?
A. China has become the world’s largest industrial N2O emitter. From 1990 to 2010, industrial N2O emissions in China grew 34-fold to 160 Gg (176,000 tons), while global industrial N2O emissions decreased by 41 percent to 379 Gg (418,000 tons) and the total industrial N2O emissions from Annex I countries (a group of industrialized and developing nations that are party to the United Nations Framework Convention on Climate Change) decreased by 71 percent to 171 Gg (188,000 tons). By 2009, the emissions from China surpassed those from the European Union and United States for the first time.
Q. The Montreal Protocol phased out chlorofluorocarbons (CFCs) and led to the still-ongoing but largely successful recovery of the ozone layer. If N2O emissions continue to rise, how will it affect this recovery?
A. N2O possesses a small ozone-depleting potential (ODP) of only 0.017, which is around one-sixtieth of CFC-11, a typical CFC regulated under the Montreal Protocol. However, its mild ODP could be quite insidious because the current anthropogenic N2O emissions are much larger than the past and future CFC emissions worldwide. This makes anthropogenic N2O emissions the single most important of the anthropogenic ozone-depleting emissions today and throughout the 21st century. If the atmospheric N2O level were to remain flat, a complete recovery of the ozone layer is projected to occur by around 2025-20281. But the increase in the atmospheric N2O level at the current pace could delay the complete recovery by a decade, although drawing down CFCs under the Montreal Protocol has provided all possible relief1.
Q. There is a lot of focus on CO2 emissions’ effects on climate change. What would happen to our climate if we dramatically reduced CO2 emissions but allowed N2O to rise unchecked?
A. Although CO2 is and will always be the largest contributor to global radiative forcing in climate change, global warming will not be alleviated if CO2 is reduced but N2O continues to rise. Currently, N2O is the third most important greenhouse gas, and its total anthropogenic emissions are projected to ascend by 58 percent and the global average N2O abundance by 13 percent by 20502.
Over 60 percent of global anthropogenic N2O emissions reside in agricultural activities. Improving fertilizer-use efficiency, applying nitrification inhibitors and controlled-released fertilizers are regarded as the most cost-effective control options3, but these practices are not widespread in most agriculture-dominant developing countries. If it remains unchecked, the increased radiative forcing — a change in the Earth’s energy balance between incoming radiation from the sun and what gets bounced back into space — could make up the net climate benefit from CO2 abatement.
Q. Are there technological solutions N2O-producing industries can implement now to reduce their emissions? How costly are they?
A. Yes, there are a few feasible technologies to abate industrial N2O emissions. But in China, the lowest cost for one such project was $10 million, and the net present value was minus $30 million (meaning the project was not profitable) for the entire 21-year operation. In my understanding, the availability of abatement technology is not an issue in the current situation, but the design and implementation of effective policies and regulatory programs are.
To read the full Q&A, click here.
Click here for the abstract.
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- Chipperfield, M., Atmospheric science: nitrous oxide delays ozone recovery. Nature Geoscience 2009, 2, (11), 742-743.
- Intergovernmental Panel on Climate Change (IPCC), Contribution of working group I: the physical science basis. In Fifth Assessment Report of the Intergovernmental Panel on Climate Change, Thomas, S.; Qin, D.; Gian-Kasper, P., Eds. Cambridge University Press: Cambridge, United Kingdom and New York, USA, 2013.
- Kanter, D.; Mauzerall, D. L.; Ravishankara, A.; Daniel, J. S.; Portmann, R. W.; Grabiel, P. M.; Moomaw, W. R.; Galloway, J. N., A post-Kyoto partner: Considering the stratospheric ozone regime as a tool to manage nitrous oxide. Proc. Natl. Acad. Sci. USA 2013, 110, (12), 4451-4457.