What is Climate?

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

20. http://maps.grida.no/go/graphic/climate-feedbacks-the-connectivity-of-the-positive-ice-snow-albedo-feedback-terrestrial-snow-and-vegetation-feedbacks-and-the-negative-cloud-radiation-feedbackhttp://maps.grida.no/go/graphic/climate-feedbacks-the-connectivity-of-the-positive-ice-snow-albedo-feedback-terrestrial-snow-and-vegetation-feedbacks-and-the-negative-cloud-radiation-feedback • http://www.epa.gov/climatechange/glossary.html#ClimateFeedback • http://www.ncdc.noaa.gov/oa/climate/gases.html • http://www.ossfoundation.us/projects/environment/global-warming/feedbacks