HALF the Earth could become too hot for human habitation in less than 300 years, Australian scientists warn.
New research by the University of NSW has forecast the effect of climate change over the next three centuries, a longer time scale than that considered in many similar studies.
The research suggests that without action to cut greenhouse gas emissions, average temperatures could rise as much as 10 to 12 per cent by 2300.
The research, produced in partnership with Purdue University, in the US, is published today in the American scientific journalProceedings of the National Academy of Sciences.
''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 2 degrees Celsius by 2100,'' said Professor Tony McMichael, from the Australian National University, in an accompanying paper published in the journal.
''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.''
Professor McMichael said that 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''.
Professor McMichael and co-author Associate Professor Keith Dear, also from ANU, described the study as ''important and necessary'' because there was a need to refocus government attention on the health impacts of global temperature rise.
There was also a real possibility that much of the existing climate modelling had underestimated the rate of global temperature rise, they said.
Dr Dear said scientific authorities on the issue, such as the United Nations 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.''