The United Nations's (UN) chief climate science body says there is no doubt last week's extreme heat in Australia is part of a global warming trend.

More than 250 of the world's top climate scientists are meeting in Hobart today to prepare the next major report from the Intergovernmental Panel on Climate Change (IPCC).

They have vowed to deliver "scientifically defensible" findings when the report is released in just over eight months' time.

Speaking to AM, IPCC chairman Rajendra Pachauri says the world is on track for a rise in temperature of between 1.1C to 6.4C.

"Now this depends on the kind of economic growth you get, a whole lot of other drivers that would essentially lead to climate change," he said.

"But if you're going to end up towards the upper end, then that clearly is a very, very serious outcome that we're looking at.

"You will get more heatwaves - we already are getting more frequent heatwaves - and we are also going to get extreme precipitation events.

"If you look at the trend, it's pretty unmistakeable and any proper analysis would tell you we are heading in that direction."

In December, a draft of the report was leaked on climate sceptic websites, in a move Dr Pachauri describes as "very unfortunate".

"It certainly goes against the agreement that you have with the expert reviewers," he said.

"Every page of the draft report clearly carries this expectation that this is confidential, because this is a work in progress."

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'Solid, robust, defensible'

Dr Pachauri says scientists are still working very hard on the final report.

"It's entirely possible that what we get in the final version may be far stronger or in some cases maybe a little more moderate," he said.

"I wouldn't go by any of the conclusions that people have seen as part of the draft report.

"But I'm absolutely certain that what we will get is a very solid, very robust and scientifically defensible report."

He said the IPCC would look at whether there was any need to change processes in the wake of the leak.

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"On the one hand we are supposed to be as open as possible and we should get as many expert reviewers as possible," he said.

"In the second order draft we've had over 31,000 comments.

"We don't want to restrict it to a point where people might say that you only get your own chosen people to comment on the report."

But he said drafts should not be made public because they could be misleading and "may not give you the true picture of what the report will finally contain".

He remains confident of the potential for global action on climate change.

"I am concerned, no doubt, but I also have a high opinion of human wisdom that I think at some stage we will bring about change," he said.

"I mean the world did act on the Montreal Protocol, the whole problem of depletion of the ozone layer and it happened very fast.

"Now I expect that perhaps this, as is the case, is going to take a little longer, but hopefully we will get action across the board."