Past efforts to save the ozone layer may have even made its danger worse.
The danger is simple nitrous oxide, which dentists know of as "laughing gas."
The Montreal Protocol of 1987 limited CFCs and that has helped the ozone layer, which protects the earth from UV radiation, but nitrous oxide was not part of that protocol.
Now, with CFC use declining, nitrous oxide has become a bigger threat, say A.R. Ravishankara, J.S. Daniel and Robert W. Portmann of NOAA's Earth System Research Laboratory (ESRL), in part because the chlorine in CFCs offset the damage from nitrous oxide.
Simply adding CFCs to the atmosphere would not help, the NOAA scientists add. The nitrous oxide offset is more than made up for by the ongoing damage from CFCs.
That is partly because while the ozone-destroying impact from CFCs is much greater than that of nitrous oxide, there is a lot more nitrous oxide.
The fact that nitrous oxide impacts atmospheric ozone has been known a long time. What the NOAA study tells us is just how much damage it is doing to the ozone layer.
Nitrous oxide is actually a double threat. It's a greenhouse gas speeding global warming, much more damaging than carbon dioxide. But when it gets into the high atmosphere it is broken down into nitrogen oxide, which seeks out the extra oxygen in ozone (which consists of three atoms of oxygen), meaning less ozone. (Remember ozone at ground level is bad. Ozone in the upper atmosphere is good.)
The bigger problem is that what Ronald Reagan said about trees applies here. Natural processes create nitrous oxide.
It's a byproduct of the use of nitrogen fertilizers, even natural fertilizers like cow manure. It's also created in the burning of trees and biofuels, as well as by industrial processes. There are few "point sources," like power plants or refrigerators, that can be plugged against the nitrous oxide hole.
Thus nitrous oxide pollution, the NOAA scientists say, is increasing at one-quarter of one percent each year. Doesn't sound like much, but that's a small percentage increase on a big number.
The good news is that given its role as a greenhouse gas the Kyoto Protocol does deal with nitrous oxide. Unfortunately that treaty expires in 2012 and efforts to craft a successor have been unsuccessful. And
Kyoto has not worked that well anyway.
The best way toward mitigation is to reduce the use of nitrous oxide in industry and try to limit the use of nitrogen fertilizers. Again, easier said than done. But the planet has no choice.