Atmosphere and Climate Chapter 7

THE ATMOSPHERE

The Atmosphere Many nearby planets, like Mars and Venus, are barren and lifeless. What allows life on Earth? The earth has an atmosphere. The atmosphere is a thin layer of gases that surrounds the Earth. It extends from the surface of the earth to hundreds of kilometers above the surface.

The Atmosphere The atmosphere is 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. The most important of the air’s gases are oxygen and carbon dioxide

The Atmosphere The Earth’s atmosphere also protects living things from most of the sun’s harmful ultraviolet radiation. At the same time, the atmosphere allows visible light to reach the Earth’s surface, supplying energy and making photosynthesis possible. The atmosphere also radiates some heat back to Earth, thereby warming the planet.

The Atmosphere The atmosphere is divided into 5 individual layers. The layers become less dense the farther they are from earth’s surface.

1. Troposphere It extends from the earth’s surface to about 6-10miles above the surface. It contains nearly 90% of the atmosphere’s gases. The air we breathe is part of the troposphere. It is also the layer in which most weather occurs.

2. Stratosphere The air in the stratosphere is less dense. Commercial airliners often travel in the lower part of the stratosphere. It contains the ozone layer, which protects us from harmful UV light from the sun.

3. Mesosphere, 4. Thermosphere & 5. Exosphere The gases in these layers become thinner and thinner until the exosphere merges with outer space.

CLIMATE

Climate Weather is simply what is happening in the atmosphere at a particular place at a particular moment. Climate, on the other hand, is the average weather in an area over a long period of time. Important aspects of climate are: temperature, humidity, wind, and precipitation. Climate, particularly temperature and precipitation, determines what types 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 an area. The most important of these factors is latitude.

Latitude Latitude is the distance from the equator, measured in degrees north or south of the equator. The equator is defined as 0°. The most northerly latitude is the North Pole, at 90° north, while the most southerly is the South Pole, at 90° south.

Latitude Latitude strongly influences climate because of the amount of solar energy an area receives depends on its latitude. More solar energy falls on areas near the equator that on areas closer to the poles.

Atmospheric Circulation Patterns There are three important properties of air that will help in the understanding of how air circulation affects climate. 1. cold air sinks and warms as it sinks 2. warm air rises and cools as it rises 3. warm air can hold more water vapor than cold air can.

Atmospheric Circulation Patterns Solar energy heats the ground, which warms the air above it. The warm air rises and cooler air moves into replace it. Heating of the atmosphere therefore causes wind, or the movement of air within the atmosphere. Because different latitudes receive different amounts of solar energy, the patterns of global circulation result.

Atmospheric Circulation Patterns

Ocean Circulation Patterns Ocean currents have a great effect on climate because water holds large amounts of heat. The movement of surface ocean currents is caused largely by winds and the rotation of the earth. These currents redistribute warm and cool masses of water.

Ocean Circulation Patterns

Seasonal Changes in Climate The seasons are a result of the Earth’s orbit around the sun.

Seasonal Changes The Earth is tilted at about 23° relative to the path of its orbit. This tilt means that the angle at which the sun’s rays strike the earth changes as the earth moves around the sun. During spring and summer in the Northern Hemisphere, the N. hemisphere tilts toward the sun and receives concentrated, direct sunlight. During fall and winter, the situation is reversed.

Seasonal Changes The four seasons familiar to many people in the world do not occur in the tropics, which are regions close to the equator. The temperatures are high and constant throughout the year because most areas receive nearly direct sunlight year-round.

Greenhouse Earth

The Greenhouse Effect The Earth is similar to a greenhouse. The atmosphere acts like the glass. 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.

The Greenhouse Effect Not every gas in our atmosphere traps heat this way. The gases that do trap and radiate heat are called greenhouse gases. The major greenhouse gases are water vapor, carbon dioxide, chlorofluorocarbons (CFCs), methane, and nitrous oxide. After water vapor, carbon dioxide is the most important of the greenhouse gases.

Carbon Dioxide In 1958, a geochemist named Charles Keeling began to measure the amount of carbon dioxide in the earth’s atmosphere. He noticed that during the winter months, carbon dioxide levels rose and during the summer months they dropped. After only a few years of measuring, it was apparent that the levels were getting higher in the winter and not dropping as much in the summer.

Carbon Dioxide What might be the cause of the rise and fall of the level during the winter and summer months? Plants use carbon dioxide to grow, so... During summer months the levels drop and during the winter months they rise. It is in correlation with the amount of plant growth.

Carbon Dioxide

Where is the extra Carbon Dioxide coming from? Fossil fuels come from plants that have been buried for millions of years. These plants become coal, oil, or natural gas. When they are burned, they release the stored carbon as carbon dioxide. Millions of tons of carbon dioxide are poured into the atmosphere each year. There is also a significant release of carbon dioxide from the burning of large areas of forest.

Greenhouse gases and the Earth’s temperature Since greenhouse gases trap heat near the Earth’s surface, many scientists think that the increase in carbon dioxide has resulted in an increase in Earth’s temperatures. This predicted increase in temperature is called GLOBAL WARMING.

A Warmer Earth Scientists are not sure how quickly the earth will warm or how severe the effects will be. Different computer models give different answers to these questions.

A warmer Earth If the Earth heats up significantly, the oceans will absorb more heat energy, which makes hurricanes and typhoons more common. Scientists are also concerned that the ocean currents may change, leading to droughts in some areas and major flooding in others.

A Warmer Earth 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 the water expands as it warms. As a result of higher sea levels, some coastal areas might be covered with water.

The Ozone Shield The stratosphere contains the Earth’s ozone shield. Ozone is a form of oxygen with molecules made of three oxygen atoms. Ozone absorbs most of the UV light from the sun. UV light is very harmful to organisms because it can damage the genetic material in living cells. The ozone layer is like “sunscreen” for the earth.

Ozone Eaters CFCs (chlorofluorocarbons) were thought to be miracle chemicals. They are nonpoisonous, nonflammable, non-corrosive metals. At Earth’s surface, CFCs are chemically stable. CFCs are now known to destroy our protective ozone layer.

The Ozone Hole Data collected by satellites since 1979 shows a significant decrease in the amount of ozone at the poles. As the amount of Ozone decreases, more UV light is able to pass through to Earth’s surface. There are many detrimental effects of ozone thinning and increased UV penetration.

The Ozone Hole

Stopping Ozone Eaters In 1987, the Montreal Protocol called for a sharp decrease in the production of CFCs. In 1992, 93 countries decided upon the following agreements: Industrialized countries must eliminate CFCs Industrialized agreed to help developing countries stop using CFCs Banning of other substances that were also harmful to the ozone.