My top five
most likely causes,
of the minor
warming / cooling
temperature cycles
(with a full cycle
that seems to last
from five hundred years,
to fifteen hundred years,
per ice core proxy studies).
Alternating minor
cooling periods
(harmful) and
minor warming
periods (beneficial),
happen between
the much more
important,
approximately
100,000 year cycle,
of peak glaciations
(the last peak was
20,000 years ago):
(1) unknown natural causes
(2) the sun,
(3) oceans and clouds
(4) measurement error /
warming bias
(5) man made CO2