Planet Earth will be too hot for humans to inhabit in just 300 years, a group of scientists are saying.

Australian scientists have warned half the planet could "simply become too hot" for human habitation by the year 2300.

New research by the University of NSW has forecast the effect of climate change over the next three centuries, a longer time horizon than that considered in many similar studies.

It suggests without action to cut greenhouse gas emissions, mankind's activities could prompt average temperatures to rise as much as 10 to 12 per cent in the next three centuries.

The research, produced in partnership with the Purdue University in the United States, is published in the US-based scientific journal Proceedings of the National Academy of Sciences (PNAS) on Tuesday.

"Much of the climate change debate has been about whether the world will succeed in keeping global warming to the relatively safe level of only two degrees celsius by 2100," said Professor Tony McMichael, from the Australian National University (ANU), in an accompanying paper also published in the PNAS.

"But climate change will not stop in 2100, and under realistic scenarios out to 2300, we may be faced with temperature increases of 12 degrees or even more."

Prof McMichael said if this were to happen, then current worries about sea level rises, occasional heatwaves and bushfires, biodiversity loss and agricultural difficulties would "pale into insignificance" compared to the global impacts.

Such a temperature rise would pose a "considerable threat to the survival of our species", he said, because "as much as half the currently inhabited globe may simply become too hot for people to live there".

Prof McMichael was joined by co-author Associate Professor Keith Dear, also from the ANU.

They describe the UNSW-Purdue study as "important and necessary" as, they said, there was a need to refocus government attention on the health impacts of global temperature rise.

There was also a real possibility, they said, that much of the existing climate modelling had underestimated the rate of global temperature rise.

Dr Dear said scientific authorities on the issue, such as the UN's Intergovernmental Panel on Climate Change (IPCC), had struck a cautious tone in forecasting future temperature rise and its impact.

"In presenting its warnings about the future, the IPCC is very careful to be conservative, using mild language and low estimates of impacts," Dr Dear said.

"This is appropriate for a scientific body, but world governments - including our own - should be honest with us about the full range of potential dangers posed by uncontrolled emissions and the extremes of climate change that would inevitably result."

- AAP