Chapter 7:Atmosphere and Climate

“The atmosphere is the key symbol of global interdependence.”

Margaret Mead, American Anthropologist

7.1 The Atmosphere

• Earth is surrounded by a mixture of gases known as the atmosphere

• Nitrogen, oxygen, carbon dioxide and other gases are all parts of this mixture

• The atmosphere changes constantly as these gases are added and removed (ex: animals take in O2, give off CO2; plants take in CO2 and give off O2; volcanic eruptions add gases; cars add and remove gases)

• Our atmosphere (this layer of gases) is what makes life possible on the Earth by insulating Earth’s surface, slowing the rate at which heat from the sun is lost, thus allowing us to survive

• Extends from the surface of Earth to hundreds of kilometers above the surface

How Photosynthesis Changed the Atmosphere

• Earth’s early atmosphere probably contained very little oxygen; early organisms (bacteria) evolved the ability to perform photosynthesis

• During photosynthesis, some oxygen from water and carbon dioxide formed oxygen gas, which entered the air

• As plants multiplied, oxygen in the air increased• Organisms, during cellular respiration, release carbon

dioxide into the atmosphere, creating the balance between the two; thus, sustaining the balance for life on Earth and keeping the planet within a temperature range for life to exist

Composition of the Atmosphere

• AIR = 78% nitrogen (entering when volcanoes erupt, dead plants and animals decay) and 21% oxygen (primarily produced by plants); remaining 1% is made up of water vapor, argon, carbon dioxide, methane and other gases

• Most important gases for organisms is oxygen (cellular respiration) and carbon dioxide for plants (photosynthesis)

• Atmosphere protects Earth’s organisms by: protecting from sun’s ultraviolet radiation, allows light to reach the surface and keeps the Earth’s temperatures stable

Air Pressure

• Earth’s atmosphere is pulled toward Earth’s surface by gravity making the atmosphere denser near the surface

• Almost the entire mass of Earth’s atmospheric gases are located with 30 km of the surface; fewer gas molecules are found at altitudes above 30 km (less pressure to push downward)

• Air becomes less dense as elevation increases; breathing becomes more difficult the higher you go

The Layers of the Atmosphere

• Atmosphere is divided into 4 individual layers (less dense the farther away from Earth) based on temperature changes that occur at different distances above the Earth’s surface

• Troposhere – closest to the earth; extends from surface outward about 18 km; contains 90% of atmosphere’s gases; layer where weather occurs; most dense atmospheric layer; temperature decreases as altitude increases

The Layers of the Atmosphere…continued

• Stratosphere – extends from 18 km to about 50 km (about 30 miles); temperature rise as altitude increases as a result of ozone in the stratosphere absorbing the sun’s ultraviolet energy and warming the air

• Ozone (O3) is a molecule made up of three oxygen; almost all O3 is concentrated in ozone layer in the stratosphere; Because ozone absorbs UV radiation, it reduces the amount of UV radiation that reaches the Earth. UV rays cause damage to living cells

The Layers of the Atmosphere…continued

• Mesosphere – extends from 50 to 80 km; coldest layer of the atmosphere, measured as low as -93 degrees C.

• Thermosphere – extends from 80 to 550 km; located farthest from Earth’s surface; nitrogen and oxygen absorb solar radiation which results in temperatures above 2000 degrees C. (wouldn’t feel hot because air particles are so far apart they never collide, so little heat is transferred)

• Nitrogen and oxygen (lower region of thermosphere) absorb harmful radiation (x-rays, gamma rays) causing them to become electrically charged (called ions). The lower region of the atmosphere is sometimes called the ionosphere. These ions radiate energy as light and oftentimes glow in spectacular colors in the night sky (North and South poles)

7.2 Energy in the Atmosphere

• Energy from the sun is transferred in Earth’s atmosphere by three mechanisms: radiation, convection, and conduction

• Radiation is the transfer of energy across space and in the atmosphere; ex: when you stand near a fire, the warmth you feel is from radiation

• Conduction is the flow of heat from a warmer object to a colder object when in direct contact

• Convection is the transfer of heat by air currents; hot air rises, cold air sinks. Ex: if you hold your hand above a hot iron, you will feel the heat because it is rising off the iron

Heating of the Atmosphere• Solar energy reaches Earth as electromagnetic radiation

(includes visible light, infrared radiation and ultraviolet light); sun releases vast amounts of radiation, Earth receives about 2 billionths of that energy

• The small amount of radiation we receive amounts to a lot of energy; about half of the solar energy ever reaches the Earth’s surface, the rest is absorbed or reflected in the atmosphere by clouds, gases and dust

• If the Earth would continually absorb that energy, it would grow hotter and hotter; however, the oceans and the land radiate the energy they have absorbed back into the atmosphere

• Dark colored objects absorb more energy than light colored objects, therefore they release more heat; cities are hotter that country sides because of this.

The Movement of Energy in the Atmosphere

• Air that moves up, down and sideways causes Earth’s weather

• In the troposphere. Currents of less dense air rise into the atmosphere, begin cooling and then sink back to the Earth’s surface

• The continual process of warm air rising and cool air sinking moves air in a circular motion, called a convection current

7.3: Climate

• Weather is happening at a particular place at a particular moment; climate is the average weather in an area over a long period of time

• Important aspects of climate are: temperature, humidity, wind and precipitation (rain, snow, hail and sleet)

• Climate determines what type of organisms are able to live in a region

What Determines Climate?

• Climate is determined by a variety of factors, including latitude, air circulation, ocean currents and the local geography of the area

• The most important factor is climate

Latitude

• Latitude is the distance from the equator; measured in degrees north or south of the equator

• Equator is 0°; most northerly latitude is 90° north (North Pole); most southerly latitude is 90° south (South Pole)

• Latitude influences climate: equator receives the most direct solar energy because it is directly overhead and is concentrated on a smaller area; poles receive less energy because the sun is lower in the sky and the sunlight is spread out over a larger area

Low Latitudes

• Latitude strongly influences climate because amounts of solar energy an area on Earth receives depends on its latitude

• More solar energy falls on areas near the equator and is more concentrated on a small surface area

• Regions near the equator have about 12 hours daylight and 12 hours of night year round

• Temperatures are high year-round, with no summers or winters

High Latitudes

• Regions closer to the poles, the sun is lower in the sky; this causes a reduction in the amount of energy arriving on the surface of the Earth

• Northern and Southern latitudes, sunlight hits Earth at an oblique angle and spreads out over a larger surface area

• Yearly temperatures near the poles are much lower than they are at the equator; the range is very large

• Hours of sunlight vary depending on the season; summers (at 45 degrees N or S) can be as long as 16 hours; winters as little as 8 hours.

• Near the poles, the sun sets for only a few hours each day during summer and rises only for a few hours in winter

Atmosphere Circulation Patterns

• Three (3) important properties of air affect climate: cold air sinks and warms as it sinks, warm air rises and cools as it rises, warm air holds more water vapor than cold air can

• Heating of the atmosphere causes wind; different latitudes get different amounts of solar energy resulting in global circulation which, in turn, determines the amount of precipitation at different latitudes

• Equator (0°) gets heavy rain (450 cm per year or 177 inches); at 30° north and south are generally warm and dry (most deserts found here); at 60° winds are beginning to rise again and drop again around 90° causing very cold deserts

Global Circulation Patterns

Cool air normally sinks, but cool air over the equator cannot descend because hot air is rising below the cool air

Cool air is then forced away from the equator toward the poles At 30 degrees north latitude and 30 degrees south latitude, air

accumulates in the upper atmosphere; some air sinks back to Earth’s surface (gradually getting warmer) which moves across the surface, causing water to evaporate from the land, creating dry conditions

Air ascending at 30 degrees north and 30 degrees south latitude move toward the equator or flow to the poles, air moving toward poles warms while near the surface; at 60 degrees north and south latitude, the air collides with cold air traveling from the poles; the warm air rises, reaching the top of the troposphere, where a small part returns back into the circulation pattern between 60 degrees and 30 degrees north and south latitude. However, most of this uplifted air is forced toward the poles.

Prevailing Winds

• Winds that blow predominantly in one direction throughout the year are called prevailing winds

• Because of rotation of the Earth, they do not blow directly north or south but to the right in the Northern Hemisphere and to the left in the Southern Hemisphere

• Primarily produced between 30 degrees north and south latitude and the equator; these belts of winds are called trade winds; blow from northeast in the Northern Hemisphere; blow from the southeast in the Southern Hemisphere

• Prevailing winds known as westerlies are produced between 30 and 60 degrees north and south latitude; in Northern Hemisphere these westerlies are southwest winds; in Southern Hemisphere they are northwest winds

• Polar easterlies blow from the poles to 60 degrees north and south latitude

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7.4 Ocean Circulation Patterns

• Ocean currents have a great effect on climate because water holds a large amount of heat

• Movement of currents is a result of winds and rotation of Earth

• Oceans make climates more moderate; coastal areas usually have warmer winters/cooler summers

• Coastal areas will usually get more precipitation than inland areas

El Nino – Southern Oscillation

• El Nino is the name given to the short-term (6 – 18 month period) periodic change in the location of warm and cold water masses in the Pacific Ocean; weak western Pacific Ocean winds strengthen and push warm water eastward; rainfall follows the warm water eastward and produces increased rainfall in the southern half of the US and in equatorial S. America; drought in Indonesia and Australia

• During La Nina, water in the eastern Pacific Ocean is cooler than usual

• El Nino and La Nina are opposite phases: El Nino is the warm phase of the cycle and La Nina is the cold phase

Pacific Decadal Oscillation

• This is the long term (20-30 year) change in the location of warm and cold water masses in the Pacific Ocean.

• Influences the climate in the northern Pacific Ocean and North America

• Affects ocean surface temperatures, air temperature and precipitation patterns

Topography

• Latitude does affect climate; however, height above sea level also has an effect on climate. Ex: Mt. Kilimanjaro (Tanzania) is 3° south of the equator but has snow covered peaks year round

• Plants and animals living in the mountains will resemble those living in cold, northern climates

• Mountains and mountain ranges also affect precipitation ex: Sierra Nevada mountains (California) – coastal side is very moist and receives a great deal of rain; the eastern side is the Great Basin Desert; this effect is called a rain shadow

Other Influences on Earth’s Climate

• Both sun and volcanic eruptions influence Earth’s climate; at a solar maximum the sun emits an increased amount of UV radiation, producing more ozone; this increase warms the stratosphere as well as the lower atmosphere and surface of the Earth

• Large-scale volcanic eruptions spews sulfur dioxide into the upper atmosphere, which can remain there for up to 3 years; it reacts with smaller amounts of water vapor and dust forming a bright layer of haze that reflects enough sunlight to cause global temperatures to decrease.

Seasonal Changes in Climate

• Temperature and precipitation change with the seasons, but what causes the seasons? The Earth’s orbit around the sun and the tilt on its axis

• During spring and summer in the Northern Hemisphere, it is tilted toward the sun, receiving more concentrated, direct sunlight; Southern Hemisphere is tilted away receiving less concentrated sunlight. During fall and winter, the situation is reversed

• Our four seasons do not occur in the tropics (close to the equator) They have high constant temperatures throughout the year and receive the most direct sunlight year round

7.5 Greenhouse Earth

• When you get into a car in the summer, you may notice that it is hotter in the car than outside the car. This occurs when light energy from the sun streams in through the glass (absorbed by the carpet and upholstery and is changed into heat energy. Heat energy cannot flow back out through the glass, it gets trapped by the glass and continues to heat up

• This is the same principle which is applied when building a greenhouse for growing plants

The Greenhouse Effect

• Earth is similar to a greenhouse; outer space is icy cold, Earth’s atmosphere acts like the glass of a greenhouse trapping the heat from the sunlight

• Heat radiates up from the Earth, some escapes into space but most is trapped by the gases in the troposphere and warms the air

• Not all gases trap this heat, but the ones that do are called greenhouse gases (water vapor, carbon dioxide, chlorofluorocarbons (CFC’s), methane and nitrous oxide)

• Water vapor and carbon dioxide are the most important

Measuring Carbon Dioxide in Our Atmosphere

• 1958, Scientist, Charles Keeling installed instruments in Hawaii (Mauna Loa volcano) to measure the amount of CO2 in the air; winds blow pretty steady and have come thousands of miles across the Pacific Ocean

• By 1994, those levels had more drastic differences, summer levels did not fall as low as in 1958 and winter levels were higher (358 ppm)

• During photosynthesis, plants take in carbon dioxide, release oxygen; carbon is not returned to the air until the plant dies or the leaves fall

• Most of the CO2 released into the air dissolves in the ocean or is used by plants for photosynthesis; causing CO2 levels in the air to vary with the seasons; summer, CO2 levels decrease (plants use it), in winter, CO2 levels naturally rise

Rising Carbon Dioxide Levels

• In less than 50 years, CO2 levels in the atmosphere have risen by over 20%

• Carbon is released into the air when burning these fossil fuels and when burning plants; millions of tons of carbon dioxide is released into the air from power plants

• They have been able to determine CO2 levels in the atmosphere for thousands of years by analyzing ice cores drilled from ice sheets; much higher levels today than they have been for probably the last 20 million years.

Greenhouse Gases and the Earth’s Temperature

• Greenhouse gases are trapped near the Earth’s surface; scientists feel this will result in a warmer Earth.

• Data collect over the last 160,000 years supports that view• Today, we are releasing more carbon dioxide into the atmosphere than any

other greenhouse gas; power plants burn coal or oil, cars burn gasoline, millions of trees are being burned in tropical rainforests…all this is contributing to the increase of CO2 in our atmosphere

• We are also releasing significant amounts of other greenhouse gases like CFC’s, methane and nitrous oxide

• Scientist feel that with the increased gases we will be raising the Earth’s temperature by at least 2°by 2050 (global warming)

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7.6 Global Warming

• The average temperature of Earth’s surface has increase during the 20th century; also known as global warming

• The temperature has been rising at a similar rate as the increase in greenhouse gases, scientists believe the greenhouse gases have caused the increase in temperature; thousands of experiments and computer models support this hypothesis

• Increase in temperatures is predicted to continue throughout the 21st century; does not mean temps are rising at a constant rate or that they are rising in all parts of the world.

• We do, however, experience natural climatic variability, which means that temperatures change naturally over the centuries; so this change cannot be ruled out.

Modeling Global Warming

• Computer models are used to predict future changes in climate; equations are written by scientist that represent the atmosphere and oceans, then CO2 levels, prevailing winds and other variables are entered into it; the resulting models are used to predict factors like temperature and sea levels will be affected

• Weather forecasters use similar programs; as you know, programs and models are not always accurate (ex: get rained on when it was predicted to be dry)

• Computer models are becoming more reliable as more data is available and additional variables are added

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The Consequences of a Warmer Earth

• Earth’s climate has dramatically changed in the past; ice ages came and went

• These changes occur over hundreds or thousands of years

• Scientists don’t know how quickly the Earth will warm or how severe the effects will be

• In North America, tree swallows, Baltimore orioles and robins are nesting about 11 days earlier than they did 50 years ago; In Britain, at least 200 species of plants are flowering up to 55 days earlier in the year than 40 years ago

The Consequences of a Warmer Earth

• There is no evidence that global warming is the cause but the nesting of birds and flowering of plants are influenced by temperature

• Scientists cannot predict how quickly Earth will warm or how severe the effects will be; different computer models give different predictions

• However, the possible effects of global warming can create a number of potentially serious environmental problems (ex: changes in weather patterns, rising sea levels)

Melting Ice and Rising Sea Level

• As polar regions warm, icebergs may break and melt in the sea resulting in a rise in the sea level

• The result of the rise in the sea level will cause coastal areas to become covered with water; coastal wetlands and other low-lying areas will become flooded, people will lose their homes and sources of income, beaches will be eroded, salinity levels of bays and estuaries will increase and affect marine fisheries, and coastal freshwater aquifers could become too salty to be used as sources of fresh water.

Global Weather Patterns

• If it heats up significantly, oceans will absorb more heat energy resulting in an increase of hurricanes and typhoons

• Scientists are concerned about changes in ocean current patterns if there are changes in the world’s weather; some areas may get more rain (flooding) than normal and other areas may get even less (severe droughts)

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Human Health Problems

• Warmer average global temperatures pose potential threats to human health

• Greater numbers of heat related deaths could occur; very young and very old city dwellers are at the greatest risk during heat waves

• People with allergies to pollen would suffer more as a result of the increase in growing time for flowering plants

• Warmer and longer summers could allow mosquitoes to establish themselves in areas which are too cold for them now (ex: bring diseases like malaria, dengue fever and encephalitis)

Agriculture

• Agriculture will be greatly affected if there are severe weather changes

• Some of the most fertile, productive areas may get hotter and drier resulting in a shift northward for farming rather than the areas where farming is prevalent today

• We would see decreased crops yields and higher demand for irrigation, further depleting aquifers

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Effects on Plants and Animals

• Climate change could alter both the range of plant species and the composition of plant communities; trees colonizing cooler areas, forest could shrink in the warmer part of their range, lose of diversity

• Could cause a shift in the geographical range of some animals (ex: migrating birds may not have to go as far south for winter, warm surface water in the ocean might cause a reduction in zooplankton, and warming in tropical waters ma kill the algae that nourish corals, killing the coral reefs)

Recent Findings

• Intergovernmental Plan on Climate Change (IPCC) is a network of about 2,500 of the world’s leading climatologists from 70 countries; they provide future estimates about the state of the global climate system

• Findings have included: the average global surface temperatures have increases by 0.6 degrees C during the 20th century, snow cover and ice extent have decreased and average global sea level has risen

• They also have reported that atmospheric greenhouse gases have continued to increase as a result of human activities and predict that human influences will continue to change the composition of the Earth’s atmosphere throughout the 21st century

Reducing the Risk

• In 1997, representative from 160 countries met and set timetables for reducing emissions of greenhouse gases; this treaty is called the Kyoto Protocol (ratified by 55% of the attending nations)

• Kyoto Protocol requires developed countries to decrease emissions of carbon dioxide and other greenhouse gases by an average of 5% below their 1990 levels by 2012; US decided not to ratify the Kyoto Protocol.

Slowing the Temperature Change

• How can we slow down global warming?• Use less fossil fuels will lessen the release of carbon

dioxide into the atmosphere• Preserve Earth’s existing forests and plant more trees;

this will help remove carbon dioxide from the atmosphere

7.7: The Ozone Shield

• The Ozone Shield is located in the stratosphere; ozone is a form of oxygen made up of 3 oxygen atoms

• Ozone absorbs most of the UV (ultraviolet) rays from the sun

• UV rays damage the genetic material in living cells• The ozone shield acts like a sunscreen for the Earth and

the inhabitants

Chemicals That Cause Ozone Depletion• During the 1970’sscientists believed Chlorofluorocarbons (CFC’s)

might be damaging the ozone shield; CFC’s are nonpoisonous, noncorrosive (do not corrode metals) and nonflammable, man-made chemicals (thought to be the miracle chemical) used in refrigerators and air conditioners (coolants)

• Also used as a gassy “fizz” when making plastic foams (styrofoam) and as a propellant in spray cans (deodorants, insecticides and paints)

• CFC’s are chemically stable at the Earth’s surface; break apart high in the stratosphere where UV radiation is powerful enough to break down CFC molecules

• Over a period of 10 – 20 years, CFC molecules releases at the Earth’s surface make their way into the stratosphere, each CFC molecule contain between one and four chlorine atoms; one single chlorine atom can destroy 10,000 ozone molecules.

The Ozone Hole

• 1985, scientists reported a study about the ozone layer near Antarctica and how it had thinned by 50% to 98%; first news about the ‘ozone hole’

• Hole fluctuates depending on the time of year; greater during the summer months when the UV light is breaking apart the CFC molecules, less during winter when they are building up

• 1997, ozone over Canadian Arctic was down to 45% below normal

How Does the Ozone Hole Form?

• During the dark polar winter, strong circulating winds over Antarctica, called the polar vortex, isolate cold air from surrounding warmer air. The air within the vortex grows extremely cold; when temperatures fall below about -80 degrees C, high altitude clouds made of water and nitric acid begin to form (polar stratospheric clouds)

• On the surface of these clouds, the products of CFCs are converted to molecular chlorine; when sunlight returns to S Pole in spring, molecular chlorine splits into two chlorine atoms by UV radiation; chlorine atoms destroy ozone causing a thin spot, or ozone hole, which can last several months (up to 70% of ozone layer can be destroyed during spring)

How Does the Ozone Hole Form?

• Ozone is produced by air pollution so why doesn’t the ozone repair this hole? Because ozone is very chemically reactive. Ozone produced by pollution breaks down or combines with other substances in the troposphere long before it can reach the stratosphere to replace the ozone that is being destroyed

The Effects of Ozone Thinning on Humans

• As ozone decreases in the stratosphere, more UV light is able to pass through atmosphere to Earth’s surface causing an increase in skin cancer, cataracts (damages DNA)

Effects of Ozone Thinning on Animals and Plants

• High levels of UV light can kill single-celled organisms called phytoplankton that live near the surface of the ocean; disrupts the ocean food chain and reduces fish harvest

• The reduction of phytoplankton would also increase the amount of CO2 in the atmosphere

• Scientists believe the increased UV light will be especially damaging to amphibians (toads and salamanders); lay eggs that lack shells in shallow water of ponds and streams

• UV light at natural levels already kill many eggs of some species by damaging the unprotected DNA; higher levels might kill more eggs and put amphibian populations at risk

• Ecologists oftentimes use the health of amphibian populations as environmental indicators of environmental changes (sensitive)

Protecting the Ozone Layer

• In 1987, A group of nations met to take action against ozone depletion (Montreal Protocol); decided to sharply limit their production of CFC’s

• A second conference was held in Denmark in 1992; decided to:• 1. Eliminate most CFC’s by 1995; U.S. pledged to ban all• substances by 2000• 2. Set up a fund to help developing countries switch to• substitutes for CFC’s• 3. Ban other substances that harm the ozone• Battle to protect the ozone is not over, some countries still make and

use CFC’s; CFC molecules stay active for decades (up to 30 years) so it will take decades for the ozone to recover