Mining giants BHP Billiton and Rio Tinto will not be affected by new laws in the United Kingdom requiring firms to list their greenhouse gas emissions because they say they already do so.
The move introduced overnight has received mixed views in Britain, where it would be used to help calculate UK carbon taxes on more than 1,000 London-listed firms.
The UK will become the first country to make it compulsory to include emissions data in annual reports.
BHP and Rio are dual listed and trade on both the London and Australian stock exchanges and are among the largest few companies on both bourses.
A BHP spokesman said the company already calculated its emissions through its annual Sustainability Report, with the next one due in September.
In last year’s report, BHP said its carbon-based energy intensity and greenhouse gas emissions intensity were lower than its 2006 baseline, by 17 per cent and 18 per cent respectively.
That was mostly driven by the agreement to use mostly hydro-electric power at its aluminium smelter in Mozambique.
Rio Tinto produces a Sustainable Development chapter in its annual report, with emissions in 2011 lower than in 2008 but higher than in 2010.
Late last year it blamed an aluminium smelter closure in north-east England, that cost 515 jobs, on new carbon taxes there.
The carbon taxes caused energy costs to increase significantly, it said.
A minority of companies voluntarily calculate such emissions and reveal at which locations they occur in sustainability reports.