CLIMATE change sceptics are "reputable", says a key crossbench senator who could decide the fate of the Rudd government's emissions trading scheme. 

Family First Senator Steve Fielding has paid his own way to attend a Washington gathering of climate change deniers, organised by the Heartland Institute free market lobby.

Senator Fielding said climate change sceptics had raised "big questions" about the link between carbon emissions and global warming.

"These scientists are pretty reputable ... and to discount them out of hand is just foolish," he told ABC Television from Washington.

With the Rudd government's emissions trading scheme likely to pass the House of Representatives today, the pressure will soon be on the Senate to pass the scheme too.

The Coalition has indicated it will block the scheme if it is voted on before the UN climate change talks in Copenhagen in December.

This means the government's ETS will only become law, during this winter session of parliament, if the Greens, independent senator Nick Xenophon and Senator Fielding back it.

But unlike the other crossbench senators, who want bigger emission reduction targets, Senator Fielding is undecided about the science of climate change.

"You've got to challenge both sides and up until now, I, like most Australians have just believed one side of the story totally," Senator Fielding said.

"There's been never a real debate about looking at the other side of it and I think we've all just believed ... global warming is driven by carbon emissions."

Senator Fielding will meet with US Obama Administration officials today to hear arguments in favour of the need to tackle climate change.

AAP