Warming "threat": The rate of change has never been as fast as it is today. Photo: Glenn Campbell

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.

crops and livestock will also struggle with thermal and water stress.
Staple crops such as corn, rice, wheat and soybeans are assumed to face a
temperature limit of 40-45 degrees, with temperature thresholds for key
sowing stages near or below 35 degrees, the report said.