Senator Fielding yesterday released a response to information provided to him by the chief scientist, Penny Sackett, and Climate Change Minister, Penny Wong, saying it did not explain why air temperatures had not risen, instead having cooled since 1998, at the rate of the rise in carbon emissions.

That response was written by four scientists noted as climate sceptics, including a researcher at the Marine Geophysical Laboratory at James Cook University, Bob Carter.

"The Government is yet to provide conclusive evidence to support its emissions trading scheme," a statement from Mr Fielding's office said.

"Given the Climate Change Minister's response, Senator Fielding does not believe any politician can vote with any confidence for [the Government's emissions trading scheme]."

The Government yesterday released its response to three questions raised by Senator Fielding challenging the science of global warming.

The response, also written by Will Steffen, executive director of the Climate Change Institute at the Australian National University, says air temperatures as an average increased over the period 1975 and 2008. The response adds that long-term average warming is a far better indication of global warming than small snapshots of temperatures over a decade, which can be affected by natural variability.

It also says ocean temperatures and ice melts are far better indicators of climate change and both are rapidly increasing.

Senator Fielding's vote will be crucial for the Government to have its emissions trading scheme legislation pass through the Senate without the support of the Opposition. A vote this week has been blocked in effect after the Opposition succeeded on Tuesday with a motion to put it last on the list of Senate business.

But the Senate yesterday passed a motion by the Greens calling for new economic modelling by Treasury to analyse the cost of a 40 per cent reduction in greenhouse emissions on 1990 levels by 2020. The motion passed with support of the Opposition on voices.

The Greens senator Christine Milne said there was good evidence that tougher emissions reduction targets would reduce the long-term costs to the economy. "Why would the Government not even want to know the economic costs of 40 per cent cuts would be? What are they afraid of?" Senator Milne said.