basic question

BASIC QUESTION

What

When

Where

Why

How

BASIC SCIENTIFIC QUESTIONS

• Explain why….?

• Explain how….?

• How does…affect…?

• What is the meaning of…?

• Why is …important?

• What is the difference between … and

Text 1

The Greenhouse Effect

The greenhouse effect results from the interaction between sunlight and the layer of greenhouse gases in the atmosphere that extends up to 100 km (60 mi) above Earth’s surface.

Sunlight is composed of a range of radiant energies known as the solar spectrum, which includes visible light, infrared light, gamma rays, X rays, and ultraviolet light. When the Sun’s radiation reaches Earth’s atmosphere, some 25 percent of the energy is reflected back into space by clouds and other atmospheric particles. About 20 percent is absorbed in the atmosphere. For instance, gas molecules in the uppermost layers of the atmosphere absorb the Sun’s gamma rays and X rays. The Sun’s ultraviolet radiation is absorbed by the ozone layer, located 19 to 48 km (12 to 30 mi) above Earth’s surface.

About 50 percent of the Sun’s energy, largely in the form of visible light, passes through the atmosphere to reach Earth’s surface. Soils, plants, and oceans on Earth’s surface absorb about 85 percent of this heat energy, while the rest is reflected back into the atmosphere—most effectively by reflective surfaces such as snow, ice, and sandy deserts. In addition, some of the Sun’s radiation that is absorbed by Earth’s surface becomes heat energy in the form of long-wave infrared radiation, and this energy is released back into the atmosphere.

Certain gases in the atmosphere, including water vapor, carbon dioxide, methane, and nitrous oxide, absorb this infrared radiant heat, temporarily preventing it from dispersing into space. As these atmospheric gases warm, they in turn emit infrared radiation in all directions. Some of this heat returns back to Earth to further warm the surface in what is known as the greenhouse effect, and some of this heat is eventually released to space. This heat transfer creates equilibrium between the total amount of heat that reaches Earth from the Sun and the amount of heat that Earth radiates out into space. This equilibrium or energy balance—the exchange of energy between Earth’s surface, atmosphere, and space—is important to maintain a climate that can support a wide variety of life.

The heat-trapping gases in the atmosphere behave like the glass of a greenhouse. They let much of the Sun’s rays in, but keep most of that heat from directly escaping. Because of this, they are called greenhouse gases. Without these gases, heat energy absorbed and reflected from Earth’s surface would easily radiate back out to space, leaving the planet with an inhospitable temperature close to –19°C (2°F), instead of the present average surface temperature of 15°C (59°F).

To appreciate the importance of the greenhouse gases in creating a climate that helps sustain most forms of life, compare Earth to Mars and Venus. Mars has a thin atmosphere that contains low concentrations of heat-trapping gases. As a result, Mars has a weak greenhouse effect resulting in a largely frozen surface that shows no evidence of life. In contrast, Venus has an atmosphere containing high concentrations of carbon dioxide. This heat-trapping gas prevents heat radiated from the planet’s surface from escaping into space, resulting in surface temperatures that average 462°C (864°F)—too hot to support life.

Text 2

Ozone Layer

Ozone Layer is a region of the atmosphere from 19 to 48 km, above Earth's surface. Ozone concentrations of up to 10 parts per million occur in the ozone layer. The ozone forms there by the action of sunlight on oxygen. This action has been taking place for many millions of years, but naturally occurring nitrogen compounds in the atmosphere apparently have kept the ozone concentration at a fairly stable level.

The ozone layer of the atmosphere protects life on Earth by absorbing harmful ultraviolet radiation from the Sun. If all the ultraviolet radiation given off by the Sun were allowed to reach the surface of Earth, most of the life on Earth’s surface would probably be destroyed. Short wavelengths of ultraviolet radiation, such as UV-A, B, and C, are damaging to the cell structure of living organisms. Fortunately, the ozone layer absorbs almost all of the short-wavelength ultraviolet radiation and much of the long-wavelength ultraviolet radiation given off by the Sun.

In the 1970s scientists became concerned when they discovered that chemicals called chlorofluorocarbons, or CFCs —long used as refrigerants and as aerosol spray propellants—posed a possible threat to the ozone layer. Released into the atmosphere, these chlorine-containing chemicals rise into the upper stratosphere and are broken down by sunlight, whereupon the chlorine reacts with and destroys ozone molecules—up to 100,000 per CFC molecule. The use of CFCs in aerosols has been banned in the United States and elsewhere. Other chemicals, such as bromine halocarbons, as well as nitrous oxides from fertilizers, may also attack the ozone layer. Thinning of the ozone layer is predicted to cause increases in skin cancer and cataracts, damage to certain crops and to plankton and the marine food web, and an increase in atmospheric carbon dioxide (see Global Warming) due to the decrease in plants and plankton.

Beginning in the early 1980s, research scientists working in Antarctica began to detect a periodic loss of ozone in the atmosphere high above that continent. The so-called ozone “hole,” a thinned region of the ozone layer, develops in the Antarctic spring and continues for several months before thickening again. Studies conducted with high-altitude balloons and weather satellites indicated that the overall percentage of ozone in the Antarctic ozone layer is actually declining. Measurements over the Arctic regions indicated that a similar problem was developing there.

In 1985 the Vienna Convention for the Protection of the Ozone Layer was adopted. In 1987 a protocol under the Vienna Convention, known as the Montréal Protocol, was signed and later ratified by 36 nations, including the United States. A total ban on the use of CFCs during the 1990s was proposed by the European Community (now called the European Union) in 1989, a move endorsed by U.S. President George H. W. Bush. In December 1995 over 100 nations agreed to phase out developed countries' production of the pesticide methyl bromide by the year 2000. The pesticide was estimated to cause about 15 percent of the ozone depletion. Production of CFCs in developed countries ceased at the end of 1995 and was to be phased out in developing countries by 2010.

Hydro chlorofluorocarbons, or HCFCs, which cause less damage to the ozone layer than CFCs do, began to be used as substitutes for CFCs following the adoption of the Montréal Protocol. HCFCs were to be used on an interim basis until 2020 in developed countries and until 2040 in developing countries. The United States passed legislation that would ban the production of the refrigerant HCFC-22, widely used in air conditioners, by 2010. Other industrialized nations also adopted measures to end HCFC-22 production prior to 2020. But production of HCFC-22 in developing nations was estimated in 2007 to be increasing at a rate of 20 to 35 percent each year.

To monitor ozone depletion on a global level, in 1991 the National Aeronautics and Space Administration (NASA) launched the 7-ton Upper Atmosphere Research Satellite. Orbiting Earth at an altitude of 600 km (372 mi), the spacecraft measures ozone variations at different altitudes and provides thorough measurements of upper atmosphere chemistry.

The World Meteorological Organization (WMO), a specialized agency of the United Nations (UN), helps support the implementation of the Vienna Convention to protect the ozone layer. During the winter of 1995-1996 the WMO observed a 45 percent depletion of the ozone layer over one-third of the northern hemisphere, from Greenland to western Siberia, for several days. The deficiency was believed to have been caused by chlorine and bromine compounds combined with polar stratospheric clouds formed under unusually low temperatures.

The ozone hole over Antarctica reached a record size in 2001, the same year that the presence of CFCs in the atmosphere was thought to have peaked. Due to the international treaty to phase out production of CFCs, many scientists expected the ozone layer would begin to recover after the record thinning of 2001. To their surprise, however, measurements in 2006 indicated that the ozone hole had once again reached a record size. Most scientists attributed the increase in the ozone hole in 2006 to an unusually cold Antarctic winter. A study the same year by the WMO and the United Nations Environment Program, however, found that the ozone layer was recovering more slowly than predicted. This finding was expected to trigger an effort in 2007 to phase out the production of HCFC-22 more rapidly than previously planned.