Transcript What is Climate? Mountains: higher altitudes = less

What is Climate?
Climate is…
• the long-term characteristic
weather of a region.
• Determined by averaging the
weather over a long period of time
– Temperature
- Precipitation
– Air pressure
- Humidity
– Days of sunshine
Factors that Affect Climate
Evergreen, CO Climograph
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Köppen climate = BSk
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Precipitation (in.)
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Temperature (deg F)
Latitude
Topography
Proximity to
Water
Large Cities
Dry, Steppe, Average
annual temperature is
less than 18 C
Latitude
• Different areas on
the Earth receive
different amount of
solar radiation due
to the Earth’s tilt.
– Equatorial
latitudes receive
the most radiation
– Polar latitudes
receive the least
Latitude (cont’d.)
• Reason for the Seasons
– Dec-Feb: N-hemisphere
points away from sun
– Jun-Aug: N-hemisphere
points towards sun
• Equator always gets
more direct and
intense solar radiation
Latitude (cont’d.)
• Global wind patterns
(aka Hadley cells)
– Air is heated over the
equator more than at
the poles.
– Differential heating
causes the warm, low
density air to rise
– Air sinks at 30° and
90° latitude.
– Colors indicate air
temperatures
– Large arrows indicate
wind direction
Latitude Climate Zones
• Tropics
– between 23.5N & 23.5S
– hot temperatures, humid
– Trade Winds: blow from east to west, toward the equator
• Polar Zones
– from 90° to 66.5N & S latitudes
– cold temperatures and dry
– Polar Easterlies: blow from east to west, away from the poles
• Temperate Zones
–
–
–
–
between the tropics & polar zones
moderate temperatures
Can be humid or dry
Westerlies: blow from west to east
Topography
• Within each climate
zone, topographic
features affect the
climate.
• Structure of the
Atmosphere
– Increase in altitude -> colder, dryer;
fewer molecules to
absorb solar
radiation
Topography: Orographic Effect
• Windward Side of
Mountains
– air rises, cools, and
forms precipitation
• Leeward Side of
Mountains
– air descends, heats
up, and dries out the
land
– rain-shadow deserts
Large Bodies of Water
Average Monthly Temperature
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Dodge City , KS
San Francisco, CA
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• Higher moisture
availability
• Temperatures are
more moderate
• Coastal areas are
warmer in the
winter and cooler
in the summer
Large Bodies of Water (cont’d)
• Sea Breezes
– Air moves from cool
to warm
• Daytime: from sea to
land
• Nightime: from land
to sea
– Effect of
moderating area’s
temperature and
raises the humidity
Large Bodies of Water (cont’d)
• Ocean Currents
– Cold currents cool
air
– Warm currents
warm air
• Air temperatures
over land are
directly effected
by temperature
of ocean current
Large Cities
• Summer temperatures
can be 5C warmer.
• Streets, parking lots,
and buildings absorb
solar radiation.
• Absorbed solar
radiation is then reradiated back into the
atmosphere as heat.
• Pollution traps heat.
What causes climates to
change?
• Climate Forcing
– Processes that force changes in the
atmosphere
• Climate Feedback
– Indirect, secondary change in response to a
forcing mechanism
Climate Forcing Mechanisms
•
•
•
•
Greenhouse gases
Aerosols
Albedo
Incoming solar radiation
Volcanic Eruptions
Climate Feedbacks
• An interaction mechanism between
processes
– initial process triggers changes in a second
process that in turn influences the initial one.
• A positive feedback intensifies the original
process (generally, bad).
• A negative feedback reduces it (good).
Climate
Feedbacks
The Problem with Positive
Feedbacks
• Runaway Trains
• Amplification and increasing rates of
change
• http://maps.grida.no/go/graphic/climate-feedbacks-theconnectivity-of-the-positive-ice-snow-albedo-feedbackterrestrial-snow-and-vegetation-feedbacks-and-thenegative-cloud-radiation-feedback
• http://www.epa.gov/climatechange/glossary.html#Climat
eFeedback
• http://www.ncdc.noaa.gov/oa/climate/gases.html
• http://www.ossfoundation.us/projects/environment/global
-warming/feedbacks