Climate

Chapter 14Earth Science

2013-2014

What is Climate?

• Thousands of years ago, Earth had much different weather patterns than today.

• Average temperature was cooler.

• Jet stream was probably further south.

• Climatology – the study of Earth’s climate and the factors that affect past, present, and future climatic changes.

Climate: More than Just Average Weather

• Climate describes the long-term weather patterns of an area.

• Includes annual variations of temperature, precipitation, wind, and other weather variables.

• Can indicate warmest and coldest temperatures ever recorded for a location.

Normals

• Standard values for a location.

• Not intended to describe usual weather conditions.

• Most conditions are recorded at airports, where no one lives.

• Changes in elevation and proximity to large bodies of water can cause climates to vary.

What Causes Climates?

• Several reasons for climatic variations:– Latitude– Topography– Closeness of lakes and oceans– Availability of moisture– Global wind patterns– Air masses

What Causes Climate?

• Latitude– Different parts of Earth receive different amounts of solar radiation.– Tropics

• Between 23.5° north and 23.5° south of the equator.• Receives the most solar radiation.• Generally warm year-round.

– Temperate zones• Between 23.5° and 66.5° north and south of the equator.• Temperatures are moderate.

– Polar zones• From 66.5° north and south of the equator to the poles.• Solar radiation strikes the polar zones at a low angle.• Nearly always cold.

What Causes Climate?

• Topographic Effects– Water heats up and cools down more slowly than

land.– Temperatures generally decrease with altitude

mountain climates are usually cooler than those at sea level.

– Climates often differ on either side of a mountain.• Windward side – usually wet and cool.• Leeward side – the air is dry.

What Causes Climate?

• Air Masses– Have distinct regions of origin, caused primarily by

differences in the amount of solar radiation.– Also depend on whether they formed over land or

water.– Average weather conditions in and near regions of

air-mass formation are fairly similar to those exhibited by the air masses themselves.

Climate Classification

• Different areas have vastly different climates.

• We need to be able to classify them.

• Koeppen classification system– Uses temperature and precipitation.– Also takes into account the distinct vegetation found in

different climates.– Developed by Russian-born German climatologist

Wladimir Koeppen.

Koeppen Classification System

• Tropical Climates– Constant high temperatures– Some areas have up to 600 cm of rain each year– Tropical rainforests have some of the most

dramatic vegetation.– Tropical wet and dry zones:• Transition zones that border the rainy tropics north and

south of the equator.• Include savannas.

Koeppen Classification System

• Dry Climates– Cover about 30% of Earth’s land area.– Most of the world’s deserts are classified as dry climates.– Precipitation is low.– Vegetation is scarce.– Located near the tropics intense amounts of solar

radiation leads to high rates of evaporation and few clouds.

– Arid regions or deserts and semi-arid regions or steppes.• Steppes are more humid than deserts and generally separate

arid regions from bordering wet climates.

Koeppen Classification System

• Mild Climates– Humid subtropical climates

• Influenced by the subtropical high-pressure systems that are normally found over oceans in the summer.

• Southeastern U.S.• Warm and muggy summers and dry, cool winters.

– Marine west coast climates• Dominated by the constant inland flow of air off the ocean.• Mild winters and cool summers.• Abundant precipitation.

– Mediterranean climates• Influenced by the Mediterranean Sea.• Summer are generally warm.

Koeppen Classification System

• Continental Climates– Warm summer climates– Cool summer climates– Subarctic climates– Battlegrounds for clashing tropical and polar air

masses.– Experience rapid and sometimes violent changes in

weather.– Extreme temperatures with influence of tropical air

in summer and polar air in winter.

Koeppen Classification System

• Polar Climates– Constant cold.– Low precipitation.– Variation also found at high elevations.

Microclimates

• A localized climate that differs from the main regional climate.

• i.e. climbing to the top of a mountain – it becomes cooler.

Microclimates

• Heat Islands– Caused by the presence of many concrete

buildings and large expanses of asphalt.– The climate is warmer than in surrounding rural

areas.– Radiate more heat into the air than do grasslands,

wooded areas, and bodies of water.

Climatic Changes

• Changes that take place over extremely long periods of time.

• Geologic records show that in the past, Earth was sometimes much colder or warmer than it is now.

Ice Ages

• Periods of extensive glacial coverage.

• Average temperatures decreased by an estimated 5°C.

• Alternate with warm periods called interglacial intervals.

• Last ice age ended about 10,000 years ago.

• Great Lakes and Finger Lakes of central New York were scoured out as last glaciers retreated.

Short-Term Climatic Changes

• Seasons – short-term periods of climatic change caused by regular variations in daylight, temperature, and weather patterns.

• Variations are the result of changes in the amount of solar radiation an area receives.

Short-Term Climatic Changes

• El Niño– A warm ocean current that occasionally develops

off the western coast of South America.– Some areas of the world experience extreme

droughts while other areas are ravaged by heavy floods.

– Increased precipitation in California and the Gulf Coast.

– Eventually, the South Pacific high-pressure system becomes reestablished and the El Niño weakens.

Change Can Be Natural

• Studies of tree rings, ice-core samples, fossils, and radiocarbon samples provide evidence of past climatic changes.

• Some caused by:– Variations in solar activity– Changes in Earth’s tilt and orbit– Volcanic eruptions.

Changes Can Be Natural

• Solar activity– Maunder minimum – period of very low sunspot

activity closely corresponds to an unusually cold climatic episode.

– Increased solar activity coincides with warmer-than-normal climates.

Changes Can Be Natural

• Earth’s orbit– The shape of Earth’s elliptical orbit appears to

change, becoming more elliptical, then more circular, over the course of a 100,000 year cycle.

– When the orbit is more elliptical, the Earth passes closer to the Sun, and the temperatures are higher than normal.

– When the orbit is more circular, the Earth is farther from the Sun and temperatures are below normal.

Changes Can Be Natural

• Earth’s orbit– Current tilt of the Earth is 23.5°.– The angle of tilt varies from a minimum of 22.1° to

a maximum of 24.5° every 41,000 years.– Lower tilt angle may cause a decrease in

temperature difference between summer and winter, leading to expanded glacial coverage.

Changes Can Be Natural

• Earth’s Wobble– Over a period of 26,000 years, Earth wobbles as it spins

on its axis.– Currently, the axis points toward the North Star, Polaris.– By about the year 14,000, the axis will tilt toward

another star, Vega.– This change will cause winter to occur in the northern

hemisphere when Earth is farthest from the Sun, and summer when Earth is closest.

– It will cause warmer summers and colder winters than those we now have.

Changes Can Be Natural

• Volcanic activity– Immense quantities of dust are released into the

atmosphere during major volcanic eruptions.– Dust can remain suspended in the atmosphere for

several years, blocking solar radiation and lowering global temperatures.

– i.e. 1991 eruption of Mt. Pinatubo in the Philippines resulted in slightly cooler temperatures around the world the following year.

The Human Factor

• Greenhouse Effect– Results from the retention of heat by the atmosphere.– Natural heating of Earth’s surface caused by certain

atmospheric gases called greenhouse gases.– Life as we know it could not exist without the

greenhouse effect.– Theorized that it is possible to increase or decrease

the greenhouse effect by changing the amount of greenhouse gases (mainly CO2).

The Human Factor

• Global Warming– A rise in global temperatures.– Worldwide temperatures have shown an upward trend

over the past 200 years.– If the trend continues:

• Polar ice caps might melt• Sea level might rise and flood coastal cities• Deserts could spread into fertile regions• Frequency and severity of storms could increase.

– While scientists agree that global warming is occurring, they disagree about the cause.

The Human Factor

• Impact of Human Activities– Automobile exhaust is a prime source of

atmospheric CO2.– Industrial emissions and burning any fossil fuels

results in the release of carbon dioxide and other gases.

– Deforestation increases the levels.• Trees use CO2 and if there aren’t as many trees, there

will be more CO2.

The Human Factor

• Environmental Efforts– Can combat global warming by conserving energy

to reduce consumption of fossil fuels.• Turn off appliances and lights when a room is not in

use.• Turn down the thermostat in the winter and up in the

summer.• Recycling.