Chapter 7 Atmosphere and Climate The atmosphere is

Chapter 7: Atmosphere and Climate “The atmosphere is the key symbol of global interdependence. ” Margaret Mead, American Anthropologist

7. 1 The Atmosphere • Our atmosphere (this layer of gases) is what makes life possible on the Earth • Extends from the surface of Earth to hundreds of kilometers above the surface • AIR = 78% nitrogen and 21% oxygen; remaining 1% is made up of water vapor, argon, carbon dioxide, neon, helium and other gases • Most important gases for organisms is oxygen (cellular respiration) and carbon dioxide (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

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

The Five Layers • Atmosphere is divided into 5 individual layers (less dense the farther away from Earth) • Troposhere – extends from surface outward about 10 km (about 6 miles); contains 90% of atmosphere’s gases; layer where weather occurs • Stratosphere – extends from 10 km to about 50 km (about 30 miles) • Mesosphere – extends from 50 to 80 km (50 miles) • Thermosphere – extends from 80 to 500 km (310 miles) • Exosphere – extends out and merges with outer space

7. 2: 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

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

Ocean Circulation Patterns • Ocean currents have a great affect 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

Local Geography • 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

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. 3 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

More Carbon Dioxide in Our Atmosphere • 1958, Scientist, Charles Keeling installed instruments in Hawaii to measure the amount of CO 2 in the air; determined that CO 2 levels in summer fall, winter they rise (314 ppm) • 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)

Where is the Extra Carbon Dioxide Coming From? • During photosynthesis, plants take in carbon dioxide, release oxygen; carbon is not returned to the air until the plant dies or the leaves fall • The ones that do not decay but are covered by sand or silt (after millions of years underground) become coal, oil or natural gas • 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

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; 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 (called global warming)

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

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)

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

Sea Levels • As polar regions warm, icebergs may break and melt in the sea resulting in a rise in the sea level • Water expands as it melts • The result of the rise in the sea level will cause coastal areas to become covered with water

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 • Limit greenhouse gas emissions

7. 4: 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

Ozone Eaters • Chlorofluorocarbons (CFC’s) might be damaging the ozone shield; nonpoisonous, noncorrosive 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)

Breaking Apart CFC’s • CFC’s are chemically stable at the Earth’s surface; break apart high in the statosphere where UV radiation is powerful enough to break down CFC molecules • CFC molecules contain between one and four chlorine atoms; one single chlorine atom can destroy 10, 000 ozone molecules

The Effects of Ozone Thinning • As ozone decreases, more UV light is able to pass through stratosphere to Earth’s surface causing an increase in skin cancer, cataracts • High levels can kill one-celled organisms that live near the surface of the ocean (can disrupt the balance of food chains), reduce microscopic photosynthesizers, increasing CO 2 in the atmosphere

The Ozone Hole • 1985, scientists reported a study about the ozone layer near Antarctica and how it had tinned 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

Stopping the Ozone Eaters • 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