Family First Senator Steve Fielding has written to senators on both sides of politics urging them to demand more proof from the Government that carbon emissions are the main driver of climate change.

Senator Fielding remains unconvinced that human activity is causing climate change and says there is evidence to show that over the past 15 years global temperatures have not risen in line with escalating carbon emissions.

His letter to senators appeals to them to consider the issue before casting their vote, which he says is too important to take along party lines.

He also believes there are Labor senators who do not agree that carbon emissions are responsible for climate change.

"There are a number of them I believe that also aren't convinced that carbon dioxide is the major cause of climate change, and that's the reason why I'm writing to both Labor senators and Liberal senators," he told ABC News Online.

"I would say that there are, on both sides of Parliament, those people who don't believe that carbon dioxide is the major driver of climate change.

"So what I'm doing is asking each senator to consider an inconvenient fact; the issue of air temperatures and why they haven't risen over the last 15 years."

In June Senator Fielding met with climate change scientists and sceptics during a fact-finding trip to the USA.

On his return he met with Australia's chief scientist Penny Sackett, but says she failed to convince him that human activity is pushing up global temperatures.

However, despite his doubts the senator says he still has not decided how he will vote on the legislation, which is due before the Senate in August.

But he maintains he is not a climate change sceptic, and attended a breakfast speech by climate change guru Al Gore this morning.

The Government wants its emissions trading legislation passed before the Copenhagen talks, but its future is uncertain.

Late last week Prime Minister Kevin Rudd said he was pessimistic that an international deal on global emissions would be struck at talks in Copenhagen in December.

Senator Fielding says that only strengthens the case for Australia to hold off on an emissions trading scheme until other major economies act.

The Coalition also wants to wait until after December.

The Greens, who hold the balance of power with Senator Fielding and Independent Senator Nick Xenophon, will vote the scheme down unless emissions reduction targets are dramatically lifted.

The Government has committed to emissions cuts of between 5 to 25 per cent of 2000 levels depending on the strength of agreement reached at the Copenhagen talks.