Health impacts in Australia in a Four Degree World - Four Degrees of Global Warming - page 141

9 Health impacts in Australia in a

Four Degree World

Anthony J. McMichael

Introduction
Two plus two equals four, though not when considering impacts in a warming
world. Much of the recent modelling of the impacts (physical, ecological and
biological) of human-induced warming has assumed global temperature increases
this century of the order of 2°C. But what of the impacts at around 4°C? The
magnitude of risks to human health in a world that is an average of 4°C warmer
than in pre-industrial times (circa ad 1750) will not be simply twice the risks
due to 2°C warming. Biological organisms and ecological systems are not simple
mechanistic Newtonian devices. When living entities are exposed to increasing
external stressors, the increase in impact is generally not linear - indeed, a
different type of impact can emerge once a critical threshold of stress is passed.
As the average temperature rises in Australia, there will be a similar upward-
turning escalation of climatic impact on many aspects of human health and
wellbeing. Assorted disorders, diseases, distress and deaths will occur at much
higher rates. The non-linear risk increase, the likely exceeding of some thresholds
and uncertainty about future configurations of other social and environmental
influences on health outcomes preclude a comprehensive projection of climatic
impacts on health and survival in an Australia where the global average
temperature has risen by 4°C or more (a Four Degree World). Guesses and highly
qualified speculations are possible, but we must recognize that we are moving
even further 'into the unknown' when contemplating a future Four Degree
World and the resultant, potentially very damaging, changes in environmental
and social conditions.
To start at the simpler end of the health-impact spectrum, we can be confident
that the projected increase by one or more orders-of-magnitude in the frequency
of very hot episodes in a 1 4°C Australia (see Braganza et al., 2013, Chapter 3 in
this volume) will have serious health consequences - especially in a population
that may already be carrying into late adulthood the detrimental health-eroding
legacy of having been overweight and obese in childhood more than a half-
century earlier. Similarly, 1 4°C warming will greatly increase the other great
weather extremes for which the young and homesick Dorothea Mackellar pined
in her iconic poem 'My Country', written in London a century ago. Deaths,