ClimateClimate

Environmental ScienceEnvironmental Science

Weather vs. ClimateWeather vs. Climate

WeatherWeather – an area’s temperature, – an area’s temperature, precipitation, humidity, wind speed, precipitation, humidity, wind speed, cloud cover, and other physical cloud cover, and other physical conditions over a short period of timeconditions over a short period of time

ClimateClimate – a region’s general pattern – a region’s general pattern of atmospheric weather conditions of atmospheric weather conditions over a long period of timeover a long period of time• Average temperatureAverage temperature and and average average

precipitationprecipitation are the 2 main factors are the 2 main factors determining climatedetermining climate

Much of the weather we experience is the Much of the weather we experience is the result of moving air masses.result of moving air masses.

The boundary between different air The boundary between different air masses is called a masses is called a frontfront..

The most dramatic changes in weather The most dramatic changes in weather occur along fronts.occur along fronts.

Warm FrontsWarm Fronts

When a warm air mass moves in it pushes When a warm air mass moves in it pushes out the cooler air mass. out the cooler air mass.

A moist warm front can bring days of A moist warm front can bring days of cloudy skies and gentle rain.cloudy skies and gentle rain.

Cold FrontsCold Fronts

Because cold air is denser than warm air, a cold Because cold air is denser than warm air, a cold front stays close to the ground and pushes the front stays close to the ground and pushes the warm air up and out of the way.warm air up and out of the way.

An approaching cold front can produce rapidly An approaching cold front can produce rapidly rising air that produces thunderstormsrising air that produces thunderstorms

ClimateClimate

In addition to average temperature In addition to average temperature and average precipitation other and average precipitation other factors influence climatefactors influence climate• Latitude Latitude • Air Circulations PatternsAir Circulations Patterns• Ocean CurrentsOcean Currents• Local GeographyLocal Geography

LatitudeLatitude Latitude determines Latitude determines

how much of the sun’s how much of the sun’s rays directly strike the rays directly strike the surface.surface.

Air is heated more at Air is heated more at the equator where the the equator where the sun’s rays strike directly sun’s rays strike directly than at the poles where than at the poles where they strike at an anglethey strike at an angle

As a result, air masses As a result, air masses are heated at the are heated at the equator and move equator and move toward the cooler poles.toward the cooler poles.

Air Circulation PatternsAir Circulation Patterns

As the earth rotates about its axis, As the earth rotates about its axis, the equator rotates faster than the the equator rotates faster than the polespoles

The rotation causes the air masses The rotation causes the air masses that are moving toward the poles to that are moving toward the poles to be deflected east or westbe deflected east or west

This sets up belts of air movement This sets up belts of air movement across the planet called across the planet called prevailing prevailing windswinds or or trade windstrade winds

Warm air rises and cool air sinks, this Warm air rises and cool air sinks, this causes wind.causes wind.

As warm air rises it cools down.As warm air rises it cools down. Any moisture in the air will condense Any moisture in the air will condense

forming clouds and finally rain.forming clouds and finally rain. At the equator, the warm air that At the equator, the warm air that

rises is pushed away from the rises is pushed away from the equator as it cools setting up global equator as it cools setting up global air movement.air movement.

Ocean CirculationOcean Circulation

Oceans absorb heat from the air Oceans absorb heat from the air circulation patterns and the suncirculation patterns and the sun

Like air, warm water rises and cold Like air, warm water rises and cold water sinks.water sinks.

The differences in water The differences in water temperatures cause water circulation temperatures cause water circulation in ocean currentsin ocean currents

Currents are also driven by winds Currents are also driven by winds and the rotation of the earth.and the rotation of the earth.

Warm ocean currents make climates Warm ocean currents make climates mildermilder• The Gulf Stream makes the climate of The Gulf Stream makes the climate of

Great Britain much warmer than Great Britain much warmer than Northern Canada even though they are Northern Canada even though they are at the same latitudeat the same latitude

Heat is absorbed and released more Heat is absorbed and released more slowly by water than land. As a slowly by water than land. As a result oceans and large lakes result oceans and large lakes moderate the climate of near by moderate the climate of near by landslands

Local GeographyLocal Geography

Various features of the surface will Various features of the surface will create local climatic conditions that create local climatic conditions that are different from the general are different from the general climate of the region.climate of the region.• MountainsMountains• LakesLakes• CitiesCities

Rain Shadow EffectRain Shadow Effect Caused by air pushed upwards at a mountain, Caused by air pushed upwards at a mountain,

cooling, and dropping it’s moisture.cooling, and dropping it’s moisture. Leads to arid climates on Leads to arid climates on leeward sideleeward side of of

mountain and wetter climates on the mountain and wetter climates on the windward windward sideside

Great Basin Desert on leeward side of the Great Basin Desert on leeward side of the SierrasSierras

Cities also create their own Cities also create their own microclimates.microclimates.

Brick, asphalt, and other building Brick, asphalt, and other building materials absorb heat.materials absorb heat.

Buildings block wind flowBuildings block wind flow Cars and air conditioning release Cars and air conditioning release

large amounts of heat and pollutantslarge amounts of heat and pollutants Cities tend to have higher Cities tend to have higher

temperatures and lower wind speeds temperatures and lower wind speeds than rural areasthan rural areas