Emissions trading market in pollution-licenses is more widely applicable than the market in emission-licenses. The international community began the long process towards building effective international and domestic measures to tackle GHG emissions (carbon dioxide, methane, nitrous oxide, hydroflurocarbons, perfluorocarbons, sulphur hexafluoride) in response to the increasing assertions that global warming is happening due to man-made emissions and the uncertainty over its likely consequences. That process began in Rio in 1992, when 160 countries agreed the UN Framework Convention on Climate Change (UNFCCC). The UNFCCC is, as its title suggests, simply a framework; the necessary detail was left to be settled by the
Nitrous oxide and thus creates foam. Used in this way, it produces whipped cream four times the volume of the liquid, whereas whipping air into cream only produces twice the volume. If air were used as a propellant, oxygen would accelerate rancidification of the butterfat, but nitrous oxide inhibits such degradation. Carbon dioxide cannot be used for whipped cream because it is acidic in water, which would curdle the cream and give it a seltzer-like "sparkling" sensation. The whipped cream produced with nitrous oxide is unstable, however, and will return to a more liquid state within half an hour to one hour.