Atmosphere Changes - Greenhouse Gases

When we talk about climate change, we are really talking about atmosphere changes due to greenhouse gases. Here’s an introduction on the subject.

Greenhouse gas concentrations in the atmosphere have historically varied as a result of many natural processes including volcanic activity, changes in temperature, etc. However, since the Industrial Revolution humans have added significant amounts of greenhouse gases in the atmosphere by burning fossil fuels, cutting down forests and other activities. Because greenhouse gases absorb and emit heat, increasing their concentrations in the atmosphere will tend to have a warming effect. But the rate and amount of temperature increase is not known with absolute certainty. Changes in the atmospheric concentration of the major greenhouse gases are described below:

Carbon Dioxide:

Carbon dioxide (CO2) concentrations in the atmosphere increased from approximately 280 parts per million (ppm) in pre-industrial times to 382 ppm in 2006 according to the National Oceanic and Atmospheric Administration's (NOAA) Earth Systems Research Laboratory, a 36 percent increase. Almost all of the increase is due to human activities (IPCC, 2007). The current rate of increase in CO2 concentrations is about 1.9 ppmv/year. Present CO2 concentrations are higher than any time in at least the last 650,000 years (IPCC, 2007).
 
Methane:

Methane (CH4) is more abundant in the Earth’s atmosphere now than at any time in at least the past 650,000 years (IPCC, 2007). Methane concentrations increased sharply during most of the 20th century and are now 148% above pre-industrial levels. In recent decades, the rate of increase has slowed considerably.
 
Nitrous Oxide:

Nitrous oxide (N2O) has increased approximately 18 percent in the past 200 years and continues to increase. For about 11,500 years before the industrial period, the concentration of N2O varied only slightly. It increased relatively rapidly toward the end of the 20th century (IPCC, 2007).

Tropospheric Ozone:

Tropospheric ozone (O3) is created by chemical reactions from automobile, power plant and other industrial and commercial source emissions in the presence of sunlight. It is estimated that O3 has increased by about 36% since the pre-industrial era, although substantial variations exist for regions and overall trends (IPCC, 2007). Besides being a greenhouse gas, ozone can also be a harmful air pollutant at ground level, especially for people with respiratory diseases and children and adults who are active outdoors. Measures are being taken to reduce ozone emissions in the U.S. (through the Clean Air Act) and also in other countries.

Chlorofluorocarbons:

Chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs) are used in coolants, foaming agents, fire extinguishers, solvents, pesticides and aerosol propellants. These compounds have steadily increased in the atmosphere since their introduction in 1928. Concentrations are slowly declining as a result of their phaseout via the Montreal Protocol on Substances that Deplete the Ozone Layer.

Others:

Fluorinated gases such as hydrofluorocarbons (HFCs), perfluorocarbons (PFCs), and sulfur hexafluoride (SF6) are frequently used as substitutes for CFCs and HCFCs and are increasing in the atmosphere. These various fluorinated gases are sometimes called "high global warming potential greenhouse gases" because, molecule for molecule, they trap more heat than CO2.

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