Greenhouse gases have always been a natural part of the atmosphere. The chemical properties of greenhouse gases mean that they strongly absorb and re-radiate the sun’s warmth in the atmosphere. This process maintains the Earth’s temperature at 33°C warmer than it would otherwise be, allowing life on Earth to exist.
Greenhouse Gases and Human Activity
Water vapour is the most abundant greenhouse gas. Its concentration is highly variable and human activities have little direct impact on its amount in the atmosphere. The main greenhouse gases generated by human activity are carbon dioxide (CO2), methane and nitrous oxide. There are also manufactured gases such as chlorofluorocarbons (CFCs), halocarbons and some of their replacements that make a small contribution to global warming.
Kyoto greenhouse gases:
The six greenhouse gases regulated under the Kyoto Protocol are:
Carbon dioxide (CO2)
Over the last 800,000 years, the amount of carbon dioxide in the atmosphere has varied between approximately 172 and 300 parts per million (ppm). Since industrialisation, carbon dioxide levels have risen sharply to about 390 ppm. Even in these amounts, the extra carbon dioxide is largely responsible for the increase in global temperatures.
At very small concentrations, carbon dioxide is a natural and essential part of the atmosphere, and is required for the photosynthesis of all plants.
Carbon dioxide enters and leaves the atmosphere from a number of natural sources and sinks at the earth’s surface. Since the industrial revolution, the burning of carbon-containing fuels has considerably increased the concentration of the CO2 in the atmosphere.