The Government's amended emissions trading scheme has no chance of meeting National's target of a 50 percent reduction in greenhouse gases by 2050, the Parliamentary Commissioner for the Environment said yesterday.

Parliament's finance and expenditure select committee began hearing submissions on the ETS bill today with angry scenes as Labour MPs accused National of trying to further shorten an already curtailed examination process.

Many submitters said they had been rang on Wednesday night or yesterday morning and told to appear yesterday for 10 minutes or possibly lose the right to submit.

Labour MP David Cunliffe had angry exchanges with committee chairman Craig Foss in which he said National had tried to have just one day for public submissions, but failed to get support.

Mr Foss told journalists that the committee had limited time to deal with 170 people or groups seeking to make oral submissions and not all would be heard before a deadline for reporting in early November.

The committee would sit again next week to hear more submissions.

Climate Change Minister Nick Smith defended the process, saying it was the third time a parliamentary committee had canvassed the ETS.

The current ETS had to be amended quickly otherwise Labour's version would come into force.

Once the committee did hear submissions, they were entirely conflicting versions about the merits of the amended ETS.

Environment Commissioner Jan Wright highlighted concerns about carbon credits in her short appearance.

The rationale for allocating carbon credits to polluters had not been explained and varied from sector to sector, she said.

The proposed phase-out was too slow and would never reach zero, she said. Polluters had little or no incentive to change their behaviour.

Dr Wright said the ETS as before the committee would not achieve National's goal of reducing greenhouse gases by 50 percent by 2050.

Labour, Green and ACT MPs all expressed frustration that they could not question Dr Wright for longer.

Representatives from Rio Tinto, which runs the Tiwai Point aluminium smelter in Southland, said there should be no reductions in carbon credits until its international competitors faced the same price on its carbon emissions.

Rio Tinto said Tiwai Point would be the first smelter in the world to come under an ETS and this would reduce its competitiveness.

The previous government passed an ETS just before last year's election but National put it on hold because it considered the cost to the economy would be too high.

It was revised and changes have been put into the Climate Change Response (Moderated Emissions Trading) Amendment Bill.

The ETS seeks to limit emissions, which New Zealand is required to do under international agreements, by putting a price on carbon.

Eventually all sectors of the economy will come under it, starting with industry, energy and transport in July next year.

Agriculture will come under it in 2015, two years later than under the original ETS.

It is a less rigorous scheme than the one introduced by the previous government and will halve the cost to consumers of power and petrol price rises.

Taxpayers will subsidise polluters to a greater extent during a transition period.