There was a
temperature peak,
about +2 degrees C.
warmer than today,
during the Holocene
climatic optimum,
~9,000 to 5,000
years ago.
About 8,200 years ago,
the Holocene optimum
was interrupted by a
sudden global cooling,
that lasted 200 years,
not accompanied by
atmospheric CO2
changes.
Egyptian records show
a cool climate from
about 750 to 450 BC,
with the Tiber River
freezing, and snow
stayed on the ground
for long periods.
(Singer and Avery, 2007)
During the
Roman
Warm Period
(200–600 AD)
Romans wrote
about grapes
and olives
growing farther
north in Italy
than previously
possible.
The Dark Ages
Cool Period
(440–900 AD)
540 AD was a
very cold year,
when tree rings
were retarded,
fruit didn’t ripen,
and some snow
even fell in the
summer in
Southern Europe.
In 800 AD the
Black Sea froze,
and in 829 AD
the Nile River
froze
(Oliver, 1973).
The Medieval Warm
Period (900–1300 AD)
had flourishing grain
crops, a rising elevation
of alpine tree lines,
and the building of
new towns and cities,
as the European
population more
than doubled.
Vikings took advantage
of the warm climate
to colonize Greenland
in 985 AD, after it
suddenly had favorable
open-ocean conditions
for navigation and fishing.
Wine grapes grew
about 500 km north
of present vineyards
in France, Germany,
and northern England
(Oliver, 1973;
Tkachuck, 1983).
Wheat and oats
were grown around
Trondheim, Norway,
suggesting climates
about one degree C.
warmer than present.
(Fagan, 2009).
After the Medieval
Warm Period,
temperatures in
Europe dropped
by as much as ~4° C.
in ~20 years as the
next trebnd began:
Little Ice Age
(1300-1860 AD)
There were
unusually
cold periods
in those
500+ years,
but there were
also about 25
cold-warm cycles.
During cold phases,
bitter winters and
cool, rainy summers
severely reduced
growth of cereal crops,
resulting in serious
crop failures, famines,
and diseases.
Three years of torrential
rains, beginning in 1315,
led to the Great Famine
of 1315–1317.
During colder winters,
the Thames River
in London, and canals
in the Netherlands,
froze over.
(Grove, 1988, 2004;
Fagan, 2001).
Glaciers expanded
worldwide during
the Little Ice Age
(Grove, 2004;
Singer and Avery, 2007).
Mid- seventeenth
century glacial
advances in the
Swiss Alps
gradually covered
farms, and buried
some entire villages.
New York Harbor
froze in the winter
of 1780.
Sea ice surrounding
Iceland extended
for miles in every
direction, closing
many harbors,
which caused
the population of
Iceland to decrease
by half.
Viking colonies
in Greenland died out
in the 1400s, because
food could no longer
be grown there.
None of Holocene
climatic cycles
were accompanied by
any significant change
in atmospheric
carbon dioxide levels.
The null hypothesis
is that twentieth century
warming represents
natural climate variations.
That null hypothesis
has NOT been disproven.