Barnaby Joyce is building on his claim the carbon tax will push the price of a Sunday roast to $100 by saying a single cow or lamb could cost as much as a house.

The government derided his new claim of extravagantly expensive meals as deranged.

Queensland Senator Joyce is the Nationals' Senate leader. He has been at the forefront of Opposition Leader Tony Abbott's campaign against the carbon tax and said previously consumers would not be happy ''when they're paying over $100 for a roast''.

Senator Joyce denied on Sunday Mr Abbott had exaggerated the impact of the carbon tax on prices.

''Obviously we haven't had this tax in for a year,'' he said.

Senator Joyce said the $23 a tonne tax was imposed on businesses that emitted more than the threshold of 25,000 tonnes of carbon dioxide equivalent or more each year.

''Seeing that there's a 25,000 tonne limit, and then you pay the $23-a-tonne carbon tax, you actually do have, in abattoirs around this nation, a time where they don't pay the carbon tax, when they take that next beast to actually switch over to the 25,000 tonne carbon emission limit,'' he told Channel Ten.

''That next beast costs them 23,000 by $23 which - what's that - $575,000 for a beast, so it's costing you vastly more than a $100 roast, that one.''

Senator Joyce rubbished the notion that the carbon tax was helping the environment. ''Has it become remarkably colder? Are we now living in a global nirvana because we've brought in the carbon tax?'' he said.

''No, it's exactly where we left it. However, people are poorer, people are definitely poorer because of the carbon tax, and it's done nothing to the climate.

''So the reality of this tax is coming home, that it's a broad-base consumption tax, delivered to you via the powerpoint of your house, so that everything you do in that house is going to be dearer, and the only person's going to be a benefactor of that is the Australian Taxation Office.''

Climate Change Minister Greg Combet said Senator Joyce's claims of million-dollar-plus roasts were ludicrous. ''Abattoirs emit methane, one of the most harmful of the greenhouse gases, from biological waste,'' he said.

''Where they emit more than 25,000 tonnes of carbon dioxide-equivalent greenhouse gases a year they will be liable for the carbon price.

''Treasury modelling shows the impact of this liability on meat prices is just 0.4 per cent, which has been factored into the government's household assistance.

''Furthermore, abattoirs can reduce emissions and carbon price liability through measures such as covering their waste settlement ponds and flaring the methane or using it to generate electricity.

''In these cases the liability may be reduced to zero, meaning the carbon price is doing exactly what it was intended to do.''

Joyce's $100 Roast Prediction Rubbished