The greenhouse effect is the natural process by which the Earth´s atmosphere captures some of the Sun´s radiation wavelengths, warming the Earth´s surface sufficiently enough to support life; however, human activities, including the burning of fossil fuels and deforestation have contributed to the greenhouse effect, causing global warming.
The greenhouse effect occurs because greenhouse gases, including water vapor, Carbon Dioxide (CO2) and other trace gases allow the Sun´s energy to reach the surface of the Earth; however, these same gases absorb a portion of the emitted infrared radiation, preventing it from escaping into outer space. The greenhouse effect causes warmer surface temperatures, which are essential for all life forms on Earth.
How the greenhouse effect starts
The greenhouse effect starts when incoming solar radiation, including ultraviolet rays (UV), visible light and near infrared radiation reach the atmosphere. Some amounts of this radiation are reflected back into space without reaching the Earth, while other amounts are able to pass through the atmosphere and get absorbed by land and the oceans, warming the Earth´s surface. This energy is then reemitted at longer infrared wavelengths and some is able to go back into space, but some is absorbed by greenhouse gases in the atmosphere. This interaction excites gas molecules, which emit radiated energy in all directions, warming the atmosphere. Some of this energy is reradiated both upwards and downwards to the Earth´s surface, warming it still further.
Earth´s temperature and global warming
The Earth´s temperature has been in equilibrium through the ages, maintaining a natural balance between incoming and outgoing thermal heat. This has sustained natural long periods of high and low temperatures on Earth. Geological records have shown cold and hot periods in which tropical temperatures have expanded to higher latitudes and polar temperatures have covered the entire planet. During the past century, the Earth´s temperature has undergone a rise in temperature of 0.6 ºC (1 ºF). Recently this tendency has continued due to global warming, which is attributed to the greenhouse effect, which in turn, is attributed to anthropogenic burning of fossil fuels and deforestation.
Greenhouse gases
Trace amounts of atmospheric gases, including water vapor (H2O), carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), ozone (O3) and Chlorofluorocarbons (CFCs), are some of the gases that contribute to the greenhouse effect. All these gases absorb infrared radiation emitted from the surface of the Earth, and as they do, they are excited to high energy states. All these gas molecules collide with nitrogen and oxygen, which are poor absorbers of infrared radiation. All these collisions create an increase in the air´s kinetic energy, leading to an increase in atmospheric temperature. All this increase in temperature maintains the lower atmosphere warm. These gases are naturally present in the atmosphere; however, human activities are increasing their concentrations.
Human activity
Deforestation may alter the local albedo by reducing vegetation land cover and altering the way in which the Sun`s radiation is absorbed or reflected. Estimates indicate that livestock, along with deforestation are responsible for 18% of the greenhouse global gas emissions. This percentage includes the production of methane by livestock. Estimations indicate that the cement industry is responsible for around 5% of the world´s anthropogenic CO2 emissions. It is predicted that more increases of CO2 and other greenhouse gases will cause a rise in temperature of approximately 3 ºC (5.4 ºF) by the end of this century.
Intensification the greenhouse effect by human activity is known as anthropogenic greenhouse effect. This effect is principally caused by atmospheric increases of CO2, mainly through fossil fuel burning, cement production and deforestation. It is estimated that rising ocean temperatures will increase evaporation rates contributing to the greenhouse effect. Concentrations of greenhouse gases in the atmosphere have greatly increased since the start of the industrial revolution in the mid-1800s. After the beginning of the industrial revolution, fossil burning has increased CO2 levels in the atmosphere from a 280 (ppm) in pre-industrial times to about 387 ppm in the present.
