WATER:
About 71% of Earth's surface is water (oceans):
Northern Hemisphere: 61%
Southern Hemisphere: 81%
Water warms and cools
far more slowly than land does.
The dominant
greenhouse gas
is water vapor.
Greenhouse gasses
primarily slow
nighttime cooling
of the planet.
LAND:
About 29% of Earth's surface is land:
Northern Hemisphere: 39%
Southern Hemisphere: 19%
Land area varies by latitude:
About 68% of all land
is in the Northern Hemisphere,
with only 32% of all land
in the Southern Hemisphere.
By latitude,
the highest percentage
of land area is between
30 degrees North and
60 degrees North.
The distribution of land areas
has changed significantly
over the past 750 million years.
ORBIT VARIATIONS:
Today, the planet’s orbit
places it closest
to the sun in early January
(winter in the Northern Hemisphere),
and farthest in early July
(summer in the Northern Hemisphere).
The hottest month
for global temperatures
tends to be July,
due to the distribution
of the land areas.
The planet's orbit, axial tilt,
and orientation vary,
are described by
the Milankovitch cycles: