The various chemicals that cause the climate system to warm vary considerably in their characteristics:
- How strong a warming effect they have
- How long they remain in the atmosphere
- What processes produce them
- Whether they have other positive or negative effects
For instance, methane is a much more potent greenhouse gas (GHG) than carbon dioxide (CO2), but it stays around a lot less time. CFCs and HCFCs are very powerful greenhouse gasses that are produced by a relatively small number of companies for specific applications; CO2, by contrast, is produced by most forms of economic activity everywhere.
Faced with these sorts of variation, some people have argued that having one regime for all GHGs is not the best approach. Because of the damage they cause to the Earth’s stratospheric ozone layer, CFCs are covered by the Montreal Protocol to the Vienna Convention. That limited agreement has produced about 175 billion tonnes of CO2 equivalent in emission reductions, compared to just a handful from the partially implemented Kyoto Protocol.
The advantage of putting all GHGs into the same legal instrument is that it could allow for mitigation to be balanced in the most efficient way. If Gas X is five times more problematic than Gas Y, the value of the carbon tax paid or auctioned permits purchased would also be five times greater. That way, people would focus on cutting emissions where it is cheapest and easiest to do so. The major disadvantage of bundling the GHGs together is that doing so can distort markets. One gas – HFC-23 – is so powerful and so cheap to get rid of that it has seriously skewed prices in global carbon markets. Rather than paying people huge sums of HFC-23, we should just be sharply limiting how much of the stuff people are permitted to make in the first place.
In an ideal world, it should be possible to have a well designed system that incorporates all GHGs. It should also be possible to have a series of overlapping agreements that do so. In practical terms, what the latter possibility allows is an alternative route that might be taken, if efforts to produce one big treaty continue to prove unsuccessful.