GHGs are one of the main reason of global climate change

Human activities are releasing
greenhouse gases into the atmosphere:
carbon dioxide, methane, nitrous oxide, halocarbons and others
creating the GHG effect

T he main greenhouse gases are a water vapour, carbon dioxide (CO₂), ozone (O₃), methane (CH₄), nitrous oxide (N₂O), halocarbons and other industrial gases.

Carbon dioxide is produced when fossil fuels are used to generate energy and when forests are cut down and burned. Methane and nitrous oxide are emitted from agricultural activities, changes in land use, and other sources. Artificial chemicals called halocarbons (CFCs, HFCs, PFCs) and other long-lived gases such as sulphur hexafluoride (SF₆) are released by industrial processes. Ozone in the lower atmosphere is generated indirectly by automobile exhaust fumes and other sources.

Rising levels of greenhouse gases leads to the GHG effect and are already changing the climate. By absorbing infrared radiation, these gases control the way natural energy flows through the climate system. In response to humanity’s emissions, the climate has started to adjust to a “thicker blanket” of greenhouse gases in order to maintain the balance between energy arriving from the sun and energy escaping back into space. Observations show that global temperatures have risen by about 0.6°C over the 20th century. There is new and stronger evidence that most of the observed warming over the last 50 years is attributable to human activities.

Climate models predict that the global temperature will rise by about 1.4-5.8°C by the year 2100. This change would be much larger than any climate change experienced over at least the last 10,000 years.

References:
- IPCC Third Assessment Report, 2001.
- Climate Change Information Kit, 2001. UNEP, UNFCCC.