The Green Party says the Emissions Trading Scheme is proving to be pointless, because it's not reducing greenhouse gas emissions.
The scheme has been in place since 2008 and Climate Change Minister Tim Groser has told the Green Party in response to written questions it is too soon to see a direct effect on gross emissions.
Greens' co-leader Russel Norman says the scheme is supposedly in place to reduce domestic emissions and use international trading to reduce global emissions.
But he says it is clearly not encouraging any reductions, and the Government is now weakening to scheme further.
Dr Norman says the latest changes will cost the taxpayer hundreds of millions of dollars because the scheme is not reducing emissions.