Climate and Climate Change

Environmental ScienceSpring 2011

ObjectivesExplain the difference between weather and

climate Identify four factors that determine climate Explain why different parts of the Earth have

different climates Explain what causes the seasons

Weather and ClimateWeather: is the state of the atmosphere at a

particular place at a particular moment Climate: is the long-term prevailing weather

conditions at a particular place based upon records taken

Weather and ClimatePhoenix, AZ and Seattle, WA may have the

same weather on a particular day (may be warm in both places), but climates are quite different (Phoenix is hot and dry, Seattle is cool and moist)

Factors Determining ClimateLatitude

Most important is distance from equator Atmospheric circulation patternsOceanic circulation patterns Local geography of an area Solar activity Volcanic activity

LatitudeLatitude: the distance from the equator

measured in degrees north or south of the equator

Equator: located at zero degrees latitudeNorth Pole: most northerly latitude, 90

degrees northSouth Pole: most southerly latitude, 90

degrees south

LatitudeLatitude influences climate because the

amount of solar energy an area of Earth receives depends on its latitude

LatitudeLow latitude

More solar energy falls on areas that are near equator

Incoming solar energy is concentrated on a relatively small surface area at the equator

In areas near equator night and day are about 12 hours long throughout the year

Temperatures are high year round, no summers or winters

LatitudeHigh latitude

In regions close to poles, amount of energy arriving at surface is reduced

In northern and southern latitudes, sunlight hits Earth at oblique angle and spreads over a larger surface area

Average temperatures are lowerHours of daylight vary

Atmospheric Circulation Air circulation affects climate

Cold air sinks because it is denser than warm air As cold air sinks, it compresses and gets warmer

Warm air rises Expands and cools as it rises

Warm air can hold more water vapor than cold air can When warm air cools, the water vapor it contains

may condense (rain)

Atmospheric Circulation

Wind: the movement of air within atmosphere

Atmospheric Circulation Because Earth rotates, and because different

latitudes receive different amounts of solar energy, pattern of global atmospheric circulation results Determines Earth’s precipitation pattern

Global Circulation PatternsCool air over equator cannot sink because

hot air is rising below it Cool air rises and is forced away from the

equator

Global Circulation PatternsAt about 30 degrees north and south latitude,

some of cool air sinks, becomes warmer as sinks

Warm, dry air moves across land and causes water to evaporate from land below, which creates dry conditions

Global Circulation PatternsAt about 60 degrees north and south latitude,

air collides with cold air traveling from poles Warm air risesWhen rising air reaches top of troposphere,

small amounts return back to circulation patterns between 60 and 30 degrees north and south latitude

Most of uplifted air is forced toward polesCold dry air descends at poles (cold deserts)

Prevailing WindsPrevailing winds: winds that blow in mostly

one direction throughout the year Because of rotation of Earth, deflected to the

right in the Northern hemisphere and to the left in the Southern hemisphere

Prevailing WindsTrade Winds: belts of prevailing winds

between 30 degrees north and south latitudes and the equator Blow from the northeast in Northern

hemisphere and southeast in the Southern hemisphere

Prevailing WindsWesterlies: produced between 30 and 60

degrees north and south latitudes Northern hemisphere these westerlies are

southwest winds Southern hemisphere these westerlies are

northwest winds

Prevailing WindsPolar Easterlies: blow from poles to 60

degrees north and south latitudes

Oceanic Circulation Patterns Movement of surface ocean currents is

caused mostly by winds and rotation of Earth Redistribute warm and cool masses of water

Oceanic Circulation Patterns El Nino- Southern Oscillation

El Nino and La Nina are opposite phases of ENSOEl Nino warmer phase, La Nina colder phase

El NinoShort term (6-18 months) periodic change in

location of warm and cold water masses in the Pacific Ocean

Warm water pushed eastward Increased rainfall eastward (southern half of US)

La NinaWater in the eastern Pacific Ocean is cooler than

usual

Oceanic Circulation Patterns Pacific Decadal Oscillation

Long term, 20 to 30 year change in location of warm and cold water masses in Pacific Ocean

Influences climate in northern Pacific Ocean and North America

Affects ocean surface temperatures, air temperatures, and precipitation patterns

Topography Elevation effects climateTemperatures fall by about 6 degrees C for

every 11,000m increase in elevation

Topography Mountains and mountain ranges influence

distribution of precipitation Sierra Nevada mountainsWhen warm air hits mountains it risesAs air rises, it cools, which causes rain on

western side of mountains By the time air reaches eastern side of

mountains, it is dryRain shadow effect

Other Influences on Earth’s Climate Solar maximum: sun emits an increased

amount of UV radiation UV produces more ozone, warming the

stratosphere Increased radiation can also warm the lower

atmosphere and surface of the Earth a little

Other Influences on Earth’s Climate Large scale volcanic eruptions

Sulfur dioxide gas can reach the upper atmosphere

Sulfur dioxide reacts with smaller amounts of water vapor and dust in stratosphere

Reaction forms a bright layer of haze that reflects enough sunlight to cause global temperature to decrease

Seasonal Changes in Climate Seasons result from tilt of Earth’s axis (about

23.5 degrees relative to the plane of its orbit)Because of tilt, the angle at which the sun’s

rays strike the Earth changes as the Earth moves around the sun

Seasonal Changes in Climate During summer in Northern Hemisphere, the

Northern Hemisphere tilts toward the sun and receives direct sunlight Number of daylight is greatest

During summer in Northern Hemisphere, the Southern Hemisphere tilts away from the sun and receives less direct sunlight

During summer in Southern Hemisphere, situation is reversed Southern Hemisphere tilted toward sun,

Northern hemisphere tilted away