Seasons almost entirely due to TILT of
Earth
Seasons opposite (not
the same) in N & S Hemispheres
Earths
orbit slightly elliptical
Slightly closer to the sun in N. Hemisphere
Winter
But this
changes as tilt precesses in 26,000 yr cycle
Expect
N. Hemisphere winter to be slightly milder
Positions
of continents and oceans actually more important
Effect
is important for Mars -- more elliptical orbit
Cyclic
variations in climate as tilt precesses (and tilt and ellipticity also gets slightly larger
and smaller
VERY
IMPORTANT TOPIC (Re: Global Warming)