Rio Tinto has wiped $1.22 billion off the value of its Australian alumina refineries to account for the cost of the Albanese government’s new carbon policy as lower commodity prices drove a 43 per cent slump in half-year earnings.

Lower prices for iron ore, copper and aluminium over the past six months drove Rio’s underlying half-year profit to a weaker than expected $US5.7 billion ($8.4 billion).