The Earth is warming so rapidly that unless humans can arrest the trend, we risk becoming ''extinct'' as a species, a leading Australian health academic has warned.

Helen Berry, associate dean in the faculty of health at the University of Canberra, said while the Earth has been warmer and colder at different points in the planet's history, the rate of change has never been as fast as it is today.

''What is remarkable, and alarming, is the speed of the change since the 1970s, when we started burning a lot of fossil fuels in a massive way,'' she said. ''We can't possibly evolve to match this rate [of warming] and, unless we get control of it, it will mean our extinction eventually.''

Professor Berry is one of three leading academics who have contributed to the health chapter of a Intergovernmental Panel on Climate Change (IPCC) report due on Monday. She and co-authors Tony McMichael, of the Australian National University, and Colin Butler, of the University of Canberra, have outlined the health risks of rapid global warming in a companion piece for The Conversation, also published on Monday. The three warn that the adverse effects on population health and social stability have been ''missing from the discussion'' on climate change.

''Human-driven climate change poses a great threat, unprecedented in type and scale, to wellbeing, health and perhaps even to human survival,'' they write.

They predict that the greatest challenges will come from undernutrition and impaired child development from reduced food yields; hospitalisations and deaths due to intense heatwaves, fires and other weather-related disasters; and the spread of infectious diseases.

They warn the ''largest impacts'' will be on poorer and vulnerable populations, winding back recent hard-won gains of social development programs.

Projecting to an average global warming of 4 degrees by 2100, they say ''people won't be able to cope, let alone work productively, in the hottest parts of the year''.

They say that action on climate change would produce ''extremely large health benefits'', which would greatly outweigh the costs of curbing emission growth.

A leaked draft of the IPCC report notes that a warming climate would lead to fewer cold weather-related deaths but the benefits would be ''greatly'' outweighed by the impacts of more frequent heat extremes. Under a high emissions scenario, some land regions will experience temperatures four to seven degrees higher than pre-industrial times, the report said.

While some adaptive measures are possible, limits to humans' ability to regulate heat will affect health and potentially cut global productivity in the warmest months by 40 per cent by 2100.
Body temperatures rising above 38 degrees impair physical and cognitive functions, while risks of organ damage, loss of consciousness and death increase sharply above 40.6 degrees, the draft report said.

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