What is Climate?

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What is Climate?
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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

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Factors that Affect Climate

• Latitude
• Topography
• Proximity to Water
• Large Cities

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Latitude

• Different areas on the Earth receive different
  amount of solar radiation due to the Earths
  tilt.
• Equatorial latitudes receive the most radiation
• Polar latitudes receive the least

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Latitude (contd.)

• 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

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Latitude (contd.)

• 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

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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

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Topography

• Within each climate zone, topographic features
  affect the climate.
• Structure of the Atmosphere
• Increase in altitude --gt colder, dryer fewer
  molecules to absorb solar radiation

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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

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Large Bodies of Water

• Higher moisture availability
• Temperatures are more moderate
• Coastal areas are warmer in the winter and cooler
  in the summer

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Large Bodies of Water (contd)

• Sea Breezes
• Air moves from cool to warm
• Daytime from sea to land
• Nightime from land to sea
• Effect of moderating areas temperature and
  raises the humidity

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Large Bodies of Water (contd)

• Ocean Currents
• Cold currents cool air
• Warm currents warm air
• Air temperatures over land are directly effected
  by temperature of ocean current

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Large Cities

• Summer temperatures can be 5?C warmer.
• Streets, parking lots, and buildings absorb solar
  radiation.
• Absorbed solar radiation is then re-radiated back
  into the atmosphere as heat.
• Pollution traps heat.

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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

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Climate Forcing Mechanisms

• Greenhouse gases
• Aerosols
• Albedo
• Incoming solar radiation

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Volcanic Eruptions
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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).

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Climate Feedbacks
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The Problem with Positive Feedbacks

• Runaway Trains
• Amplification and increasing rates of change

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• http//maps.grida.no/go/graphic/climate-feedbacks-
  the-connectivity-of-the-positive-ice-snow-albedo-f
  eedback-terrestrial-snow-and-vegetation-feedbacks-
  and-the-negative-cloud-radiation-feedback
• http//www.epa.gov/climatechange/glossary.htmlCli
  mateFeedback
• http//www.ncdc.noaa.gov/oa/climate/gases.html
• http//www.ossfoundation.us/projects/environment/g
  lobal-warming/feedbacks