1. What is Climate?

2. 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

3. Factors that Affect Climate
Latitude
Topography
Proximity to Water
Large Cities

4. 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

5. 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

6. 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

7. 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

8. 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

9. 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

10. Large Bodies of Water Higher moisture availability
Temperatures are more moderate
Coastal areas are warmer in the winter and cooler in the summer

11. 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

12. 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

13. 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.

14. 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

15. Climate Forcing Mechanisms
Greenhouse gases
Aerosols
Albedo
Incoming solar radiation

16. Volcanic Eruptions

17. 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).

18. Climate Feedbacks

19. The Problem with Positive Feedbacks
Runaway Trains
Amplification and increasing rates of change