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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 90 3 Köppen climate = BSk 80 2.5 60 2 50 1.5 40 30 1 20 0.5 10 0 n Ja 0 ar M ay M l Ju Month p Se v No Precipitation (in.) 70 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 23.5N & 23.5S – hot temperatures, humid – Trade Winds: blow from east to west, toward the equator • Polar Zones – from 90° to 66.5N & 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 90 80 70 Temperature 60 50 40 30 20 10 0 y ar nu Ja ry ua br Fe c ar M h ril Ap ay M ly Ju ne Ju st gu Au Month Dodge City, KS r be em pt Se San Francisco, CA O er ob ct r be em ov N r be em ec D • 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 5C 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
