2.2.3. Detection in Managed Systems
188.8.131.52. Human Health
Because many wild organisms serve as vectors for human diseases, and these
diseases are very well documented historically (with records going back hundreds
of years), one might think of using the distribution and intensity of disease
occurrence as an indicator of shifts in wild vector distributions or altered
dynamics of pathogen transmission. Many disease vectors are known to be strongly
influenced by climate (e.g., the anopheline mosquitoes that carry malaria).
The problem with using disease records is that the presence of the vector is
necessary but not sufficient to cause disease transmission. Socioeconomic factorssuch
as sanitation systems, vaccination programs, nutritional conditions, and so
forthlargely determine whether the presence of the disease in wild vectors
actually leads to outbreaks of disease in nearby human populations. In fact,
transmission and virulence of disease are themselves directly affected by climate.
Thus, although disease is a potentially important component of climate change
impacts, it is not a useful indicator of the direct effects of climate change
(see Chapter 9 and Section 19.2).
Crop plants, like plants in general, are more strongly affected by the direct
effects of increased atmospheric CO2 than are animals. Increased
CO2 alters the physical structures and the carbon/nitrogen balance
in plantswhich in turn alters the plant's growth rate, yield, susceptibility
to pest attack, and susceptibility to water stress. These effects interact with
the effects of climate change itself in complex ways. In addition, the effects
of climate change are buffered in agricultural systems as farming methods are
altered to adjust to current climate conditions (e.g., irrigation practices,
crop varieties used) (see Sections 5.3 and 19.2).
A few selected attributes and systems may be possible indicators of climate
change effects. Possible traits are leafing dates of grapevines in orchard with
old stock, and planting dates of yearly crops in areas that have not changed
seed variety over a given length of time.