Global Climate Change – Part II Previous Climate Changes
In the first of these articles on the effects of climate change, several
exaggerated scenarios were offered as ‘worst case’ climate change outcomes.
For the most part, the scientific community dismisses these as hype and
propaganda; at the same time, some experts offer us insight into the real,
probable outcomes of climate change. How does the community of experts
go about separating the hype and hysteria from the probable and predicable?
In a word, history.
Scientists need only look to the past to find the answer to the question of
what may come. Though it appears to be accelerated, this is not the first
time that the Earth’s climate has changed; some changes were regional, some
affected half the planet and others were truly global and in each case, there
are geological and archeological clues as to what happened and what resulted.
Many of these events even happened inside the bounds of human history so there
are firsthand oral or written accounts to back up the archeology.
The American Southwest is well known today as a desert region; images of
dust-covered cowboys and oasis-cities like Phoenix and Tucson spring to mind.
1,500 years ago, however, this region was wetter, even lush. The Pueblo
Peoples (sometimes referred to as the Anasazi) called the region home and
built complex, apartment-like cities into the canyon cliffs; these cities housed
many people and were continuously habited for hundreds of years. If one
stands in these monuments of the ancients today and looks out a doorway or
window the view is radically different from what the original occupants would
have seen. Today, the region receives very little rainfall and the view is one of
a dry, arid land with minimal vegetation. It is hard to imagine how these ancient
people thrived in such a harsh environment.
Archeology paints a picture of a different land when the Ancient Pueblo lived
in their cliff cities, however. Seeds found in pottery, scraps left in ancient
garbage dumps and even paintings all tell the story of a wetter, greener climate.
Recent satellite imagery shows the remnants of dry river beds and cultivated
fields in the area surrounding the Pueblo dwellings; given these facts, it is easy
to understand why the Pueblo settled in the area. In fact, the period from
about 700 AD to 1130 AD shows evidence of consistent, regular rainfall and
concurrent with the rains, there is evidence of a population boom in the region;
Native Americans migrated to the area because of abundant food and relative
peace among the peoples.
At the end of this time, native tradition tells of the Great Drought and both
geological and archeological evidence supports this; beginning in approximately
1150 AD, the continent of North America entered into a 300 year period of
radically decreased rainfall. As crops failed and water became scarce, the
Pueblo people eventually abandoned their cities, migrating to other, more
habitable locales, leaving their empty buildings to history. Other cultures were
affected by the Great Drought, as well. Half a continent away, the Mississippian
Culture declined and disappeared in the same time period.
On the European continent, the Medieval Warm Period and the Little Ice Age
provide other examples of what climates can do to cultures. The Medieval
Warm Period (MWP) is a well-documented period lasting from about
800 AD to 1200 AD; during this time, Europe experienced warm temperatures,
regular rainfall and extremely stable climate. It is not well understood by
scientists if this was indicative of global climate at the time, but it is generally
accepted that at the least, the entire North Atlantic region saw these patterns
during the MWP.
The effects of the MWP on the human population of Europe are captured in
personal writings, paintings and even tax documentation. Wine grapes grew
as far north southern Britain, crops were plentiful and the population flourished.
These were welcome changes from the previous period, often referred to as the
“Dark Agesâ€. Other evidence for the long-lasting, stable, warm climate include
the remnants of stumps that show the tree line in the Alps was several hundred
meters higher than the modern tree line. It was during the MWP that the Vikings
took advantage of ice-free seas to colonize Greenland and Iceland.
In contrast, the Little Ice Age (LIA) which occurred from about 1300 AD to
about 1850 AD, was marked by cold temperatures, extreme weather and famine.
Ice cores show evidence that in about 1250 AD, the North Atlantic Ice Pack
began to grow, slowly for the first few decades and then more rapidly in the
following century. In Europe, the climate grew colder and more prone to violent
weather events. The rains of 1315 are well documented in church and personal
journals; unusually heavy rainfall plagued European farmers in the spring of that
year; the rains continued and the temperature remained cool for the rest of the
spring and summer, preventing the crops from growing in the fields. The same
records tell of the Great Famine of 1315-1317, the first of several famines that
struck Europe with regularity in the LIA. In the end, millions perished because
of these crop failures. Paintings of the time show scenes of winter often lasting
well into when summer would be expected; and records indicate that the winters
were harsh and fiercely cold. One priest even writes of finding the communion
wine frozen one morning. Even the notoriously tough Vikings abandoned their
settlements in Greenland; in fact, some of these villages have only recently
been ‘discovered’ after the glaciers that had covered them for hundreds of years
retreated as a result of our current warming trend.
Taken as a whole, these stories all point to the fact that one predictable
outcome of climate change is unpredictability. It is fair to say that our
modern world has greater insight into the weather and science than our
forbearers but we should not let ourselves rest on that advantage. We must
be diligent in tracking changes in our climate and acting upon predicted
outcomes extrapolated from those changes. Some effects may actually be
beneficial, like the increased crop yields in the MWP, and we must be poised to
take advantage of these benefits when they emerge. Likewise, we must guard
against the crop