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Science A-Go-Go
Contrary
to common beliefs, societal collapses of the past have been
caused by sudden climate change, not only by social, political
and economic factors, Yale anthropologist Harvey Weiss reports
in a new study published in this week's Science.
"Our
conclusions are both surprising and challenging because
in the past, archaeologists and anthropologists have commonly
explained collapsed societies as the result of social, economic
and political forces combined," said Weiss, professor
of Near Eastern archaeology at Yale.
For
their study, Weiss and his colleague, Raymond S. Bradley
of University of Massachusetts, Amherst, summarized and
synthesized recent archaeological and paleoclimatological
research. This allowed them to understand that repeated
incidents of societal collapse in the archaeological and
historical past have been the product of abrupt, natural
climate changes.
"These
data force a change in some general social science understandings,"
said Weiss. "The data are also important because they
underscore the difference between past climate changes and
present-future climate change. Past climate changes were
unrelated to human activities. In contrast, present and
future climate change will involve both natural and anthropogenic
forces and will be increasingly dominated by the latter."
The
climatic events Weiss describes in the study were abrupt,
involved new conditions that were unfamiliar to the inhabitants
of the time, and persisted for decades or centuries. They
were therefore highly disruptive, Weiss said, leading to
societal collapse-an adaptive response to otherwise insurmountable
stresses.
The
study describes well-documented examples of societal collapse
dating back to about 12,500 to 11,500 years ago with the
Natufian communities in southwest Asia. This community suddenly
abandoned seasonally nomadic hunting and gathering activities
that required relatively low inputs of labor to sustain
low population densities and replaced these with new labor-intensive
subsistence strategies of plant cultivation and animal husbandry.
Weiss
said a major difference from the past is that we are now
able to foresee the results of these climate changes and
are able to understand the technological and social innovations
which could allow us to address them.
"We
also know where the population growth will be greatest,"
Weiss adds. "We must use this information to design
strategies that minimize the impact of climate change on
societies that are at greater risk. This will require substantial
international cooperation, without which the 21st century
will likely witness unprecedented social disruptions."
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