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Implications of Sun-Earth distance?
When Sun is closest during North winter (now)
- Warmer seasons, ice shrinks
- Ice shrinks, -> less reflected energy -> even warmer
- Positive feedback stops once minimum ice is reached
When Sun is farther away during Northern winter
- Colder seasons, ice grows
- Ice grows -> more reflected energy -> even colder
Southern hemisphere climate is more stable
Equatorial climate is even more stable
Notes:
The equatorial climate is the most stable and models indicate that as global averages move by 10˚C or more, equatorial averages will remain relatively constant.
The Southern hemisphere is less variable because Antarctica provides a hard limit to the ebb and flow of southern ice. The advance of snow coverage can't occur to bootstrap the advance of ice, because when snow falls in the ocean, it just melts.
The more dynamic ebb and flow of ice in the North provides an ice amplification effect. Whether ice advances or retreats depends on whether the intensity of summer was enough to melt the snow accumulated during the winter. This consequence can accumulate from year to year.