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 Latitude Topography Proximity to Water Large Cities

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 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 re-radiated 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-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