Nitrous oxide (N 2 O, aka laughing gas) apart from being a powerful greenhouse gas, 298 times more effective at trapping heat than CO 2 , is also the single most important ozone depleting gas being emitted by human activities. A paper published in this week’s ScienceXpress, Nitrous Oxide (N2O): the dominant ozone-depleting substance emitted in the 21st century, by Ravishankara, Daniel and Portman(*), shows that as the chlorofluorcarbons controlled by the Montreal Protocol have been phased out, atmospheric N 2 O has continued to increase. Here’s the abstract:

By comparing the ozone depletion potential-weighted anthropogenic emissions of N 2 O with those of other ozone depleting substances, ODSs, we show that N 2 O emission currently is the single most important ODS emission and is expected to remain the largest throughout the 21st century. N 2 O is unregulated by the Montreal Protocol. Limiting future N 2 O emissions would enhance the recovery of the ozone layer from its depleted state, and would also reduce the anthropogenic forcing of the climate system, representing a â€˜win-winâ€™ for both ozone and climate.

This graph from the paper illustrates how the impact of CFCs has declined enormously over the last 20 years, while N 2 O has taken a leading role.

Commenting on the paper, NIWA scientists Dr Paul Johnston, Dr Greg Bodeker, Dr Richard McKenzie, and Dr Olaf Morgenstern, who study atmospheric chemistry at Lauder in Central Otago, had this to say:

“The authors calculate that if anthropogenic N 2 O increases continue at current rates, by 2050 they would cause ozone depletion in excess of 30% of that produced by CFCs at the peak loss in 1987 due to CFCs. (N 2 O emissions are a byproduct of fertilizer use in agricultural, combustion, industrial process, etc.) In the 1990s the average anthropogenic emissions were estimated to be nearly 40% of the total emissions. The authors conclude that a reduction in N 2 O emissions would benefit the ozone layer, as well as benefiting climate due to the greenhouse effect of N 2 O.

N 2 O emissions are an important chunk of NZ’s overall greenhouse gas inventory, amounting to 17% of the total, so any increased focus on N 2 O could have important policy implications for emissions control in NZ. Fortunately, nitrification inhibitors – currently in use as well as being evaluated by the Pastoral Greenhouse Gas Research Consortium – offer a relatively straightforward approach to achieving reductions.

[More coverage: Nature News, Reuters, Telegraph (UK).]

* – Ravishankara, A. R., Daniel, J. S. & Portmann, R. W. Science advance online publication doi:10.1126/science.1176985 (2009).

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