Orbital-Scale Changes in Methane
qThe Vostok ice record shows a series of cyclic variations in methane concentration, ranging between 350 to 700 ppb (part per billion).
qEach Ch4
cycle takes about 23,000
years.
qThis cycle length points to a likely
connection with changes in
orbital procession.
qThe orbital procession dominates insolation changes at lower latitudes.
q
Modern interglacial period
Last
interglacial period
(from Earth’s Climate: Past
and Future)