ESS101C
Prof.
Jin-Yi Yu
Why Have Ice Sheets Grown Larger Since 0.9 Myr Ago?
qExplanation 1:
A result of the gradual (tectonic-scale) cooling.
Tectonic-scale cooling due
to the decrease of CO2
è cooling
reach a threshold value 2.75 Myr ago
è
moderate-size ice sheets can form in
northern hemisphere ice during major summer insolation minima and
disappeared completely during summer insolation maxima.
è the
falling CO2 levels continued
è cooling
reached another threshold value 0.9 Myr ago
è that ice
sheets never completely disappeared during weak summer insolation maxima
è ice
sheets began to grow larger and persist longer