Geoscience Reference
In-Depth Information
consequences (e.g. reduced food yields and consequent increases in infant/child
mortality) is easy to imagine. So too is the likely rise in trans-boundary conflicts
and environmental refugee flows.
Various studies have concluded that in a Four Degree World the already-
existing water scarcity would be greatly exacerbated, particularly in northern
and eastern Africa, the Middle East and South Asia (World Bank, 2012).
Likewise, a protracted 1 4°C world would see widespread loss of human habitat,
including coastal farmland, as slowly expanding oceans rise by two (and probably
more) metres over several centuries. If human population numbers had not
already declined by then, this would surely engender a 'slow-burn' crisis of food
shortages, poor health, starvation and conflict.
Can we learn from the distant past?
Before considering categories of health consequences of a 1 4°C Australia it is
of interest to look at the health-and-survival impacts of three of the great 2 4°C
cooling events in the long history and prehistory of human societies (McMichael,
2012). Three distinctive cooling episodes, the first two pre-historical and the
third one historical, reflect the impacts on human health and survival of major
volcanic eruptions, casting a veil of cooling ash, aerosols and debris around the
world.
First, the Toba eruption occurred about 74,000 years ago, during which global
average temperatures fell by 5-10°C for 5-10 years. This event presumably wiped
out plant and animal food sources and contaminated fresh water, and caused an
estimated 90 per cent mortality among early humans already in the South Asian
region and a close call for dispersing (Out-of-Africa) groups of modern Homo
sapiens .
Second, the Younger Dryas event, which occurred around 12,800-11,600 bp,
saw a 5-10°C drop (for instance, in Europe) occur within around 250 years. The
cooling lasted for 1,000 years, causing drying in Nile Valley and diminishing
river flows, resource conflicts and the abandonment of settlements (evidenced by
shattered skulls, spear heads), and the collapse of early Natufian proto-farming
settlements in the (Turkish) Anatolian plateau (northern region of the 'Fertile
Crescent').
Third, during the 'ad 536 Event', attributed to a volcanic eruption, average
global temperature fell by 3-4°C and persisted for 5-10 years throughout
Eurasia and beyond. This may have triggered the (bubonic) Plague of Justinian,
imported from northern Africa, and breaking out in Constantinople and
then throughout the Eastern Roman Empire (McMichael, 2012). This brief
cooling may have facilitated the survival of infected fleas travelling north
from Ethiopia (or other ancient Eastern African grain-export ports) to the
Mediterranean coast with grain shipments and their stowaway rats, destined
for Constantinople. It is also thought to be implicated in the collapse of
the Moche civilization, in coastal northern Peru, beginning abruptly around
536 ad, and in the rapid demise of 'Early Iron Age' culture associated with acute
 
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