What is What is Climate?Climate?

Climate is…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 Factors that Affect ClimateClimate

LatitudeTopographyProximity to

WaterLarge Cities

Evergreen, CO Climograph

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Köppen climate = BSk

Dry, Steppe, Average annual temperature is less than 18 ° C

LatitudeLatitude

• 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.)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.)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 ZonesLatitude 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

TopographyTopography

• 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 EffectTopography: 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 WaterLarge Bodies of Water• Higher moisture

availability• Temperatures are

more moderate• Coastal areas are

warmer in the winter and cooler in the summer

Average Monthly Temperature

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Dodge City, KS San Francisco, CA

Large Bodies of Water Large Bodies of Water (cont’d)(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 Large Bodies of Water (cont’d)(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 CitiesLarge Cities• Summer temperatures

can be 5C 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 What causes climates to change?change?

• Climate Forcing – Processes that force changes in the

atmosphere

• Climate Feedback – Indirect, secondary change in response to a

forcing mechanism

Climate Forcing MechanismsClimate Forcing Mechanisms• Greenhouse gases• Aerosols• Albedo• Incoming solar radiation

Volcanic EruptionsVolcanic Eruptions

Climate FeedbacksClimate 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 Climate FeedbacksFeedbacks

The Problem with Positive The Problem with Positive FeedbacksFeedbacks

• 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