Glencoe World GeographyChapter 3:
Climates of the EarthChapter Overviews
Climate refers to weather patterns that occur in a place over time. Although the
earth's climates are influenced by many factors, the most important is the earth's
position in relation to the sun. Other influences relate to the specific location
of a place and the features that exist there. World climate regions vary greatly,
and each supports characteristic vegetation. Human activity may be contributing
to the cycle of climate change.
Earth-Sun Relationships The amount of sunlight that reaches the earth
varies depending on Earth's tilt and rotation. Earth's revolution, or yearly
orbit around the sun, also affects the amount of sunlight each area receives,
resulting in seasonal changes. In the northern hemisphere, the solstice marks
the beginning of summer and the equinox, winter. Because of the earth's tilt
and rotation, sunlight at the Poles varies dramatically through the seasons,
ranging from continuous sunlight to long periods of darkness. The greenhouse
effect, which normally regulates heat in the atmosphere to support life, may
be changing due to increased carbon dioxide released into the atmosphere by
human activities. Factors Affecting Climate Latitude, elevation, wind and ocean currents,
and landforms all influence climate individually or in combination. The zone
of low latitudes, near the equator, receives more direct rays of the sun year
round than the zones of high latitudes near the Poles. Mid-latitudes experience
variable weather. High elevations have colder temperatures due to thinner atmosphere
that retains less heat. Wind currents carry warm and cool air around the earth
in fairly constant patterns. Warm and cold ocean currents affect the temperature
along coastal lands. The combination of water vapor and wind currents can form
patterns of precipitation. Landforms such as large bodies of water and mountain
ranges can also influence temperatures and precipitation. World Climate Patterns Geographers divide the world into climate regions,
each with its characteristic vegetation. Hot, wet tropical climates feature
tropical rain forests; dry climates include desert, with little vegetation,
and steppe, with scattered scrub and cactus. The mid-latitude climates include
four temperate climate regions of various weather patterns and seasonal changes
that support vegetation ranging from thick forests to grasslands. Highlands
and high latitude climates have much colder temperatures with mixed forests
or only mosses and lichens. Scientists are working to better understand the
evidence of past climate changes as well as the effects of human activities
on climate. |