Senior Liberal Nick Minchin says the globe is more likely to be cooling than warming and has slammed a leading climate expert as being "on the Government's payroll".

Amid fierce debate about the Government's carbon tax plan, Professor Ross Garnaut yesterday warned the scientific case for climate change had strengthened the position that the Earth is warming and that human emissions of greenhouse gases are the main cause.

Senator Minchin - who led the Liberal Party's move to dump leader Malcolm Turnbull over his support for action over climate change - says Professor Garnaut is an economist and "knows nothing about the climate".

Speaking on Sky News, Senator Minchin said: "He's not a climate scientist. I don't think he has any authority whatsoever to speak on the climate".

While saying he respected Professor Garnaut, he said: "He's on the Government's payroll, he's paid to ensure that the Government's desire to tax the hell out of us over this issue is substantiated by proclamations that the world is about to end".

Quoting a blog from an atmospheric scientist from the University of Alabama - who he did not name - Senator Minchin said: "It's clear that the models, and we're dealing with models, have grossly overestimated the sensitivity of temperature to increases in CO2.

"I think what's occurred is that there was a warming period from about '75 to the year 2000. It was part of a natural cycle of warming that comes in 25, 30-year cycles. The world has basically stabilised in terms of temperature since about 2000.

"There are many, many scientists who actually think we could be entering a cooling phase, and I for one think that is more than likely.

"We have stabilised in terms of world temperatures. There is a very powerful natural cycle at work, and if anything we're more likely to see a tendency down in global temperatures, rather than up."

The United Nations says last year was the hottest on record.

'Misinformed'

Climate Change Minister Greg Combet says Senator Minchin's comments are "misinformed" and his attack on Professor Garnaut "unwarranted".

"The fact is that at the core of the Liberal Party is the belief that climate change doesn't exist, and the party is led by somebody who thinks the climate science is 'absolute crap'," Mr Combet said.

"Mr Minchin's comments further demonstrate the Coalition's determination to run a misinformed scare campaign when it comes to climate change.

"I call on Mr Abbott to show leadership and repudiate Mr Minchin's unwarranted attacks on a leading independent and well-respected Australian."

On Thursday, Professor Garnaut released the fifth update to his 2008 report on climate change, specifically tackling climate science.

He also released specific data on temperature, sea level rises and extreme events from recent years.

"On the measurable phenomena, it does seem that certainly there's been no evidence of overstatement," he said.

"And it does seem to be a number of points of understatement, and I call that an awful reality because it would be much better if [the] opposite were true.

"It would be much better if the evidence was showing the earlier signs had overstated things."

Tax mistake

As the debate about a carbon tax heats up, an environmental economist has said it is a mistake for Australia to set a price for carbon before other countries do.

The Government's carbon tax will start in July next year and then morph into an emissions trading scheme, but the details of the tax and the amount of compensation are yet to be determined.

Australian National University Crawford School of Economics professor Jeff Bennett says the Government's policy will disadvantage local exporters, while other countries are lagging on the issue.

"The Prime Minister said we've got to do something or else we're going to be left behind - it's important to realise that first of all, very few countries around the world are doing much about this (pricing carbon)," he said.

"And secondly, even if everybody did something about, if all nations in the world did what Australia's doing, still the impact on greenhouse gases in the atmosphere would be so small, [it would] not have any real or meaningful impact on the pattern of climate across the planet.

"What that means is that the Australian economy is going to have this quite substantial cost imposed on it, with very little to show by way of benefit."

Professor Garnaut was unavailable for comment when contacted by the ABC today.