Geological studies show
the most recent major
deglaciation (glaciers
melting) started about
20,000 years ago.
The results of oxygen isotope
measurements, of ice cores
in the Greenland and Antarctic
ice sheets, several decades ago,
stunned the scientific world.
One surprise was
multiple abrupt and
intense periods of
warming and cooling
with a roughly 1,500-year
periodicity, now called
Dansgaard - Oeschger
(or D-O) events.
More than one dozen
Dansgaard-Oeschger
abrupt warming
and cooling episodes
happened in the past
50,000 years.
The most likely cause
of these major episodes
is fluctuations in
solar activity.
That's just a guess.
None of the events
were forced by changes
in levels of atmospheric
carbon dioxide.
Major post-glacial
climatic episodes are:
the Oldest Dryas (cold) Period,
the Bølling (warm) Period,
the Older Dryas (cold) Period,
the Allerød (warm) Period,
the Inter-Allerød (cold) Period, and
the Younger Dryas (cold) Period.
The end of the Younger Dryas
occurred when temperatures
rose sharply by ~12° C.,
over only about 50 years,
ending the Pleistocene ice age
about 11,500 years ago.
Since then we have been
living in the Holocene
interglacial period -- an
unusually warm period
for our planet, at least
compared with the
past 800,000 years,
studied using Antarctica
ice cores.