Chapter 7: Atmosphere and Climate Section 7.3: Greenhouse Earth Section 7.4: The Ozone Shield

Have you ever gotten into a car that has been sitting in the sun for a while with its windows up. Even if the day is cool, the air inside the car is warmer than the air outside. The reason heat builds up inside a car is that the sun’s energy streams into the car through the glass windows. The carpet and upholstery in the car absorb the light and change it into heat energy. Heat energy does not pass through the glass as easily as light energy. Light pours in, heat builds up!

The Earth is similar to the car and a greenhouse – the Earth’s atmosphere acts the glass on the car and a greenhouse.

Greenhouse Effect 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.

Not every gas in our atmosphere traps heat in this way – the gases that do trap and radiate heat are called greenhouse gases.

Major Greenhouse Gases Water vapor. Carbon dioxide. Chlorofluorocarbons (CFC’s). Methane. Nitrous oxides.

More Carbon Dioxide…. In 1958, geochemist Charles Keeling installed an instrument at the top of a tall tower on the volcano Mauna Loa in Hawaii. Keeling wanted to very precisely measure the amount of carbon dioxide in the air –away from cities and forests.

Map of CO2 Measuring Stations

Findings…. Keelings first measurements, in March of 1958, was 314 parts per million of carbon dioxide, or 0.0314 percent. The next month he found the levels had rose – however by summer they were falling and by winter they were rising again.

Why…. In the summer, plants use the carbon dioxide and reduce the levels. In the winter, the plants no longer are using carbon dioxide, however, due to the decomposition of the dead plants, carbon dioxide is given off.

Results…. After only a few years of measuring carbon dioxide levels, it became obvious that they were changing in ways other than just seasonal fluctuations. Each year the high winter levels were higher, and the summer levels did not fall as low. In 1994, the CO2 levels were measured at 0.0358 percent.

OZONE

Ozone is a form of oxygen with molecules made of three oxygen atoms.

Ozone shields the Earth’s surface from most of the sun’s harmful ultraviolet rays.

During the seventies, scientists began to worry that a class of human made chemicals called CFCs – chlorofluorocarbons – might be damaging the ozone layer.

CFCs at the Earth’s surface are stable; however, in the stratosphere they pull apart and combine with ozone – thus destroying the ozone.

Effects of Ozone Thinning No ozone layer – more UV light reaches the Earth’s surface. Cancer has risen in the past years partially due to the increase in UV light reaching the Earth’s surface. UV light kills one celled organisms. Interference with photosynthesis. More people developing cataracts.

Stopping CFCs Montreal Protocol – nations agreed to sharply limit their production of CFCs. Many developed countries banned the production of CFCs all together. Industrialized countries agreed to setup a fund to help developing countries switch to CFC substitutes.