The government will find out at noon today whether it has reaped about $1 billion from selling carbon credits, or whether it earned nothing and will have to wait until next year.
The income will be at least partly used to fund National's promised tax cuts.
The Emissions Trading Scheme requires many big fossil fuel polluters, including petrol and electricity companies, to give up one carbon credit for every tonne of carbon dioxide they emit. The annual supply of credits is capped, and the government sells them at quarterly auctions.
The money used to be ring-fenced for things like retiring coal boilers and helping towns adapt to extreme events, but that won't be the case under the coalition.