Atmosphere &Climate

Atmosphere &Climate Chapter 7

The Atmosphere Section 1

Atmosphere • A thin layer of gases that surround the Earth • Extends from the surface of the Earth to hundreds of kilometers above the surface • 78% nitrogen and 21% oxygen (the remaining 1% is made up of water vapor, argon, carbon dioxide, neon, helium, and other gases)…we call this entire mixture “air” • Protects Earth’s living things from most of the sun’s harmful UV radiation (still allowing enough light in for photosynthesis) • The atmosphere also radiates some heat back to Earth, thereby warming the planet • Without the atmosphere, life on Earth would cease to exist.

The Atmosphere and Photosynthesis • Photosynthesis: process of making food from water and carbon dioxide using sunlight for energy • Cellular respiration: process of organisms breaking down food molecules and carbon dioxide is released • There is a balance (shown on pg.174) between photosynthesis and respiration that keeps the amount of carbon dioxide in the atmosphere nearly constant. • Even though CO2 makes up only .03% of the gases in the atmosphere, this small amount helps to keep the Earth within a temperature range that can support life.

The 5 Layers of the Atmosphere: • Troposphere: • Extends from Earth’s surface to about 6 miles above the surface • Contains nearly 90% of the atmosphere’s gases • The air we breathe is part of the troposphere • Is the layer where weather occurs • Stratosphere: • Above the troposphere • The air here is less dense…winds blow here, but without the swirling turbulence of the troposphere • Commercial airliners often travel in the lower part of the stratosphere • Contains the ozone layer, which protects us from harmful UV light from the zone (will discuss more later) • Mesosphere-beyond strato • Thermosphere-beyond meso • Exosphere-beyond thermo and the gases here become thinner and thinner until the exosphere merges with outer space

Climate Section 2

Weather and Climate • Weather: • The state of the atmosphere at a particular place at a particular moment • Climate: • The long term prevailing weather conditions at a particular place based upon records taken Two places may have the same weather on a particular day, but their climates can be quite different.

What Factors Determine Climate? • Latitude (most important) • Air circulation • Oceanic currents • Local geography

The most important of the factors that determine climate is distance from the equator, or….. Latitude • The distance from the equator measured in degrees north or south of the equator is called latitude. • Latitude strongly influences climate because the amount of solar energy an area of Earth receives depends on its latitude….

Latitude Low Latitudes High Latitudes • More solar energy falls on areas near the equator than on areas closer to the poles (lower latitudes) • Near the equator, the sun is directly overhead, and its rays hit the Earth directly • The incoming solar energy is concentrated on a small area of the surface • In regions closer to the poles (high latitudes), the sun is lower in the sky and this reduces the amount of energy arriving at the surface. • Sunlight hits the Earth at an oblique angle and spreads over larger area of the surface than it does at the equator

Atmospheric Circulation: • Three important properties of air show how air circulation affects climate: • Cold air sinks and warms as it sinks • Warm air rises and cools as it rises • Warm air can hold more water vapor than cold air can. Read pages 177-179 together….

Oceanic Circulation Patterns: • Ocean currents have a great effect on climate because water holds large amounts of heat. • The movement of surface ocean currents is cause mostly by winds and the rotation of Earth. • These surface currents redistribute warm and cool masses of water around the planet. • Some surface currents warm or cool coastal areas year-round.

Local Geography • Kilimanjaro, a mountain in Tanzania, is only about 3 degrees south of the equator, but snow covers its peak year-round! Kilimanjaro illustrates the important effect that height above sea level has on climate. • Temperatures fall by about 11 degrees Fahrenheit for every 1000 meters (3,300 feet) increase in elevation. • Also, mountains influence the distribution of precipitation

What causes Seasons? • The seasons result from the tilt of Earth’s axis (about 23.5 relative to the plane of its orbit). • Because of this tilt, the angle at which the sun’s rays strike the Earth changes as the Earth moves around the sun.

Greenhouse Earth Section 3

Greenhouse Effect: • Earth is similar to a greenhouse… • The Earth’s atmosphere acts like the glass in a greenhouse and sunlight streams through the atmosphere and heats the Earth. • As heat radiates up from the Earth, some of it escapes into space…the rest of the heat is trapped by gases in the troposphere and warms the air • This process is called the greenhouse effect

Greenhouse Gases • Not every gas in our atmosphere traps heat in this way • The gases that do not trap and radiate heat are called greenhouse gases • The major greenhouse gases: • Water vapor • Carbon dioxide • Chlorofluorocarbons (CFCs) • Methane • Nitrous oxide

Greenhouse Gases &Earth’s Temperature • There is more Carbon Dioxide (greenhouse gas) in our air now than before…caused by the burning of fossil fuels (decayed plants) and the burning of living plants. • Since greenhouse gases trap heat near Earth’s surface, many scientists think that more greenhouse gases in the atmosphere will result in a warmer Earth (statistics prove this to be true) • Today we are releasing more carbon dioxide into the atmosphere…but we are also releasing other greenhouse gases (CFCs, methane, etc…) in significant amounts. • Many scientists think that as a result of increasing greenhouse gases in our atmosphere, the average temperature of the Earth will increase…this predicted increase in temperature is called Global Warming.

What changes can we expect with a “warmer Earth”? • Weather Patterns • The oceans will absorb more heat energy, which may make hurricanes and typhoons more common • May cause a change in ocean current patterns….which could affect the world’s weather…some regions might have more rain than normal, while others might have less • Agriculture • The American Midwest, which includes some of the most productive farmland in the world, is one of the regions that might get hotter and drier…with increasing average temperatures in North America, the weather patterns that are best for farming would shift northward • Sea Levels • As polar regions warm more icebergs may break loose from glaciers and melt in the sea • Sea levels would then rise, not only from melting ice but also because water expands as it warms… • As a result of higher sea levels, some coastal areas might be covered with water.

So, What Can We Do? • The use of fossil fuels could be reduced so that less carbon dioxide is released into the atmosphere • The Earth’s existing forests could be preserved, and more trees could be planted…the trees would remove carbon dioxide from the atmosphere... • In December, 1997, representatives from 150 nations met in Kyoto, Japan to debate international limits on greenhouse-gas emissions…the developed nations, including the US, agreed to cut greenhouse-gas emissions by an average of 5% below 1990 levels.

The Ozone Shield Section 4

Ozone • The Ozone Layer is an area in the stratosphere where ozone is highly concentrated. • Ozone is a molecule made of 3 oxygen atoms (O3) • The ozone layer absorbs most of the UV light (which is harmful to organisms because it can damage the genetic material in living cells) from the sun. • By shielding the Earth’s surface from most of the sun’s UV light, the ozone in the stratosphere acts like sunscreen for the Earth’s inhabitants.

Chemicals that cause Ozone Depletion • Chloroflurocarbons (CFCs): • Human-made chemicals that cause ozone depletion • CFCs are chemically stable at Earth’s surface, but break apart high in the stratosphere, where UV radiation, a powerful energy source, is absorbed. Once the CFC molecules break apart, parts of the CFC molecules destroy protective ozone. • CFCs were once used in many everyday products such as deodorants, insecticides, air freshener, and paint.

The Ozone Hole • A thinning of stratospheric ozone that occurs over the poles during the spring. • As the amount of ozone in the stratosphere decreases, more UV light is able to pass through the atmosphere and reach Earth’s surface. • The ability of more UV light to reach Earth’s surface is a problem for Earth’s inhabitants….

Damaging Effects of UV Light: • Humans • Increased incidence of skin cancer • Premature aging of the skin • Increased incidence of cataracts • Weakened immune response • Amphibians • Death of eggs • Genetic mutation among survivors • Reduction of population • Marine Life • Death of phytoplankton in surface water • Disruption of food chain • Land Plants • Interference with photosynthesis • Reduced crop yields

Protecting the Ozone Layer • Montreal Protocol • 1987 agreement among a group of nations to take action against ozone depletion by sharply limiting their production of CFCs. • Copenhagen, Denmark-1992 • 93 countries agreed upon: • Industrialized countries agreed to eliminate most CFCs by 1995. The US pledged to ban by 2000 all substances that pose a threat to the ozone layer • Industrialized countries also agreed to set up a fund to help developing countries switch to substitutes for CFCs • Other substances that destroy ozone were also banned

Atmosphere &Climate