The Greens are again asking the Government to fix its emissions trading scheme

Polluting companies bought nearly three-million credits in today's first carbon auction of the year - but more than 500-thousand credits went untouched.

The Climate Change Commission's latest advice is credits are over-supplied, lowering the incentive to stop polluting.

Greens co-leader Chloe Swarbrick says the partly successful auction shows the Government must listen.

She says there is a desperate need to bring agricultural emissions into the scheme and lower credits, or it will be an ineffective system.