Sue Boyce, from Queensland, and Judith Troeth, from Victoria, crossed the floor to vote for the ETS in the Senate last year in defiance of their new leader, Tony Abbott.

They said yesterday they were reserving their right to do the same again. The Government needs seven Senate votes to pass the scheme, which means the five Greens who voted to defeat the scheme last year would need a change of heart.

The Climate Change Minister, Penny Wong, said yesterday she would meet the Greens next week, but at this stage the minor party is holding out for a scheme far more ambitious than that which will be reintroduced into Parliament next week.

In accordance with an agreement all countries made at the Copenhagen conference to announce their proposed emissions reduction targets before January 31, Senator Wong yesterday announced Australia would stick to its conditional range of cutting emissions by between 5 per cent and 25 per cent by 2020.

In a sign of exasperation, she said Australia would lock in the unconditional target of 5 per cent by the end of next year if a binding global agreement had not been reached by then.

The Greens and climate groups were unimpressed, saying it was agreed at Copenhagen to announce a specific target, not a conditional range.

''They will continue to hold back global progress with an upper limit of 25 per cent that is still far too low, let alone the woeful 5 per cent,'' a Greens Senator, Christine Milne, said.

The proposed scheme would begin in July 2011, but the price of carbon would be fixed for the first year at $10. From July 1, 2012, it would be set by market forces and carbon trading would begin.

Senator Wong said if the world had failed to reach agreement by the end of 2011, ''the Government will set the target at 5 per cent to give business certainty from 2012 onwards''.