Understanding the Greenhouse Effect and Climate Change
The Greenhouse Effect
The term greenhouse effect describes the mechanism by which atmospheric gases, particularly carbon dioxide, trap heat near the Earth’s surface. The glass roof of a greenhouse transmits visible light and absorbs infrared (IR) radiation emitted, thus trapping heat. In a way, carbon dioxide acts as a glass roof, except that the temperature rise in a greenhouse is mainly due to restricted indoor air circulation. The transfer of carbon dioxide to and from the atmosphere is an essential part of the cycle of this element.
Solar Radiation and the Earth’s Surface
Radiant solar energy the Earth receives is distributed in a range of wavelengths from 100 to 5000 nm, but most energy is concentrated in the visible spectrum, comprising wavelengths of 400-700 nm. By contrast, the thermal radiation emanating from the Earth’s surface has wavelengths greater than 4000 nm (IR region) because the average temperature from the surface is much smaller than the Sun’s. Radiation that comes to the IR atmosphere can be absorbed by water vapor and carbon dioxide, but not by nitrogen or oxygen.
How Greenhouse Gases Trap Heat
When a molecule of water or carbon dioxide receives a photon from the IR region, it is promoted to a higher level of vibrational energy. These energetically excited molecules are unstable and very soon lose the excess energy either by collision with other molecules or by spontaneous emission of radiation. Part of this radiation is emitted to outer space and part returns to the surface of the Earth.
The Rise of Greenhouse Gases
Although the total amount of water vapor in our atmosphere has not changed much in years, the increase in carbon dioxide concentration has been constant since the beginning of the century as a result of burning fossil fuels.
In addition to CO2 and H2O, other greenhouse gases such as CFCs also contribute to global warming.
Consequences of the Greenhouse Effect
Some forecasters predict that if the accumulation of greenhouse gases continues at this rate, the Earth’s average temperature will increase by about 1-3 ยบ C in the 21st century. Although a temperature rise of a few degrees may seem insignificant, it is actually large enough to upset the delicate thermal balance of the Earth and cause glaciers and ice sheets to melt. As a result, sea level could rise and inundate coastal areas. However, it is very difficult to make predictions about climate trends, as well as to take into account other potential factors before concluding that global warming is inevitable and irreversible.
Combating the Greenhouse Effect
To combat the greenhouse effect, we must reduce CO2 emissions. This requires optimizing the energy efficiency of vehicles and systems for domestic heating and lighting. It is also important to develop energy sources to replace fossil fuels, such as photovoltaic cells. Nuclear power is a viable alternative, but its use is still very controversial because it is difficult to remove radioactive waste, plus it is more likely that there will be accidents at nuclear power plants than for conventional energy. The proposal to gradually withdraw the production of CFCs, which are the most potent greenhouse gases, will help to slow warming. Other measures to be taken to control CO2 emissions are to recover methane gas generated in sanitary deposits and decrease natural gas leaks. Finally, it is vital to conserve the Amazon and other large forests in order to maintain a stable atmospheric concentration of CO2.