SCIENCE COULD HELP SOCIETIES WEATHER RUINOUS
by Tom Siegfried
February 5, 2001
The world is full of menaces to society, and
always has been.
Throughout recorded history, and even before,
human societies have tended to fall apart. From the Natufian hunter-gatherers
to the Central American Maya to the Anasazi of the American Southwest,
cultures of great sophistication have inevitably collapsed.
Guess who's next.
Surely not the post-industrial high-tech mass-marketing
culture that rules the world today? Don't count on it.
Collapse of a society can occur rather suddenly,
say anthropologist Harvey Weiss and geoscientist Raymond Bradley.
Flourishing cultures may abruptly abandon the region they occupy,
drastically alter their way of life or radically reorganize their
social and governmental systems.
Apparently, archaeologists have commonly concluded,
various political and economic problems conspire to drive societies
to ruin. But the latest evidence suggests that the real menace
was the weather.
Recent precise dating of ancient weather changes
reveals that many cultural disruptions corresponded with drastic
"There is mounting evidence that many
cases of social collapse were associated with changes in climate,"
Drs. Weiss and Bradley wrote last month in the journal SCIENCE.
When climate changes suddenly, societies may
not be able to cope with the unfamiliar living conditions that
"Prehistoric and early historic societies
-- from villages to states or empires -- were highly vulnerable
to climatic disturbances," the scientists wrote.
About 12,000 years ago, for example, the Natufians
of southwest Asia switched their lifestyle from hunting to farming.
The impetus for that cultural shift, say Drs. Weiss and Bradley,
was a cooler, drier climate. Hunting and foraging could no longer
supply enough food, so the nomadic lifestyle collapsed and a culture
based on planting crops and raising animals arose in its place.
Then 8,200 years ago, a drought lasting about
two centuries led to abandonment of the farming settlements. Only
moister conditions millennia later allowed the rebirth of Mesopotamian
civilization. From about 2600 B.C. onward, favorable climate supported
civilizations from the Mediterranean and Egypt through Mesopotamia
to India. But many of those cultures suffered drastic change after
2290 B.C., when the weather cooled and rainfall levels dropped
Similarly, severe drought coincided with the
Maya collapse of the ninth century, and decades of drought in
the 13th century apparently forced the Anasazi to abandon their
In the past, of course, humans had no control
over climate, and their cultures were at the mercy of atmospheric
aberrations. In the future, though, climate will be conditioned
in part by the gases pumped into the air by power plants, factories
and cars. The result, most experts say, will be a warmer planet.
How warm the Earth will get, and how fast,
are of course matters of considerable uncertainty and debate.
Carbon dioxide, the principal air-warming gas, participates in
some complicated chemistry.
Plants suck carbon dioxide out of the air for
food, keeping atmospheric levels lower than they would otherwise
be. But when the plants die and decay, the carbon combines with
oxygen again and returns to warm the atmosphere.
All the carbon doesn't return to the air, though,
because some organic matter decays very slowly. Vast amounts of
carbon are stored, for instance, in the northern peatlands. In
fact, the peatlands may contain more than half as much carbon
as the amount already in the air. Writing recently in NATURE,
scientists from the University of Wales say the peat decays slowly
because it contains chemicals blocking the enzymes that cause
Enzymes are biological catalysts. Without the
right enzyme around, most biochemical reactions go slower than
a molasses-covered glacier. But the right enzyme turns the light
green and abolishes the speed limit.
In the peatlands, it seems, an enzyme called
phenol oxidase doesn't do its job of breaking up alcohol-like
chemicals called phenols. When phenols accumulate, they block
the action of other enzymes that cause decay, the Welsh scientists
Based on lab experiments and measurements in
Florida wetlands, the Welsh group concludes that lack of oxygen
keeps the phenol oxidase inactive. More oxygen would trigger that
enzyme to destroy the phenols, clearing the way for massive decay.
"This has profound implications,"
the Welsh biologists wrote. If patterns of global change dry out
the peatlands, bringing in more oxygen, reinvigorated enzyme activity
could rapidly release billions of tons of carbon into the air,
possibly causing dire climatic consequences.
This possibility is far from the only consideration
in evaluating future climate threats. But it should serve as a
signal to politicians who are cavalier about the global warming
problem. Unless they understand enzymes -- and they don't -- they
cannot appreciate how fragile the current climate may be.
So today's society may find itself in much
the same situation as the historical cultures crippled by climate
change. Except that, as Drs. Weiss and Bradley point out, scientists
now can anticipate the future.
Science's foresight could help society plan
to reduce the damage that climate change might inflict.
"This will require substantial international
cooperation," say Drs. Weiss and Bradley, "without which
the 21st century will likely witness unprecedented social disruptions."