THE IMPACT ON HUMAN HEALTH - The Climate Casino - page 92

medical technologies, and health status are evolving rapidly. I sketch
some estimates in this chapter, but it must be emphasized that these
are at best educated guesses, and the potential health outcomes range
from none to serious.
The most detailed assessment of the impacts on health was a study
undertaken by a team of health and climate scientists for the World
Health Organization (WHO). 3 Their report analyzed two mechanisms
through which health impacts occur. The fi rst is the direct effect of in-
creasing environmental stress on people due to heat waves, pollution,
and fl oods. The second is the indirect effect that occurs because global
warming may lower living standards, increase the geographical range
of some infectious diseases such as malaria, and worsen malnutrition
and diarrheal disorders.
The study team began by examining evidence of the relationship
between different diseases and climatic conditions. They then estimated
the increased risk of contracting the diseases due to changing climate.
By combining these estimates, they projected the total health risk from
climate change.
More precisely, they began with estimates of the health status of
different regions in a no-warming scenario; then they used one of the
standard warming scenarios from climate models and produced a new
estimate of health status; they then took the difference between the
two scenarios to calculate the impacts of global warming in a particular
year. 4 The team identifi ed three major areas of concern: malnutrition
(from inadequate incomes), diarrheal diseases (from poor sanitation and
health systems), and malaria (from an expansion of malarial regions).
The report used an interesting innovation in public health research—
the concept of the disability-adjusted life year (DALY). 5 The DALY
measures the loss in healthy years of life from different diseases. It
counts two factors: the number of years of life lost and the fraction of
healthy years lost. For example, if an elderly 70-year-old person with a
life expectancy of 10 years dies of heart failure, this would be 10 DALYs
lost. If a young girl in Tanzania contracts malaria, her life expectancy
would be reduced by about 33 years, so this would represent a loss of 33
DA LYs. 6