A greenhouse gas is a gas that absorbs and emits radiation within the thermal infrared range. This process is the fundamental cause of the greenhouse effect. The primary greenhouse gases in Earth’s atmosphere are water vapor, carbon dioxide, methane, nitrous oxide and ozone. Greenhouse gases greatly affect the temperature of Earth’s surface. Some substances like CFCs have been identified as having an impact on Earth but do not contain any carbon atoms.
Greenhouse gases are those gases which allow sunlight to enter into the earth’s atmosphere but trap heat from escaping back into space. The presence of these gases causes what is known as the ‘greenhouse effect’. Without them, life on Earth would not be possible as we know it. The main natural greenhouse gases are: water vapour (H₂O), carbon dioxide (CO₂), methane (CH₄) and nitrous oxide (N₂O).
The concentration of greenhouse gases in Earth’s atmosphere has increased since the Industrial Revolution due to human activity such as burning fossil fuels, deforestation and agriculture. This increase has led to a rise in global temperatures known as climate change. Climate change poses a huge threat to life on Earth and action must be taken to reduce emissions of greenhouse gases and mitigate its effects.
Water vapour is by far the most important greenhouse gas – it contributes around 60-70% of the natural ‘greenhouse effect’. However, while water vapour concentrations are increasing due to human activity (such as irrigation), its concentration in the atmosphere remains largely unaffected by our actions. Carbon dioxide (CO₂) is next most important – it accounts for 20-30% of the natural ‘greenhouse effect’. Its concentration has increased markedly since pre-industrial times due largely to burning fossil fuels such as coal, oil and gas. Methane (CH₄) contributes 10-15% towards the natural ‘greenhouse effect’. Its concentration has also increased since pre-industrial times due to human activity such as livestock farming and waste disposal . Nitrous oxide (N₂O) contributes 5-10% towards the natural ‘greenhouse effect’. Like CO₂ , its concentrations have also increased markedly since pre-industrial times due largely to agricultural activities such as fertilizer use . Ozone (O3) in boththe stratosphere and troposphere contribute around 5% each towards total radiative forcing from all well mixed long lived greenhouse gases . In addition there are many other substances which contribute very small amounts e.g perfluorocarbons(PFCs), hydrofluorocarbons(HFCs), sulphur hexafluoride(SF6) etc . Despite their low abundance they can have large impacts on climate because they remain inthe atmosphere for very long periods of time(decades or centuries )and have high global warming potentials(GWPs).
There are two key ways in which anthropogenic emissions can alter atmospheric concentrations 1.) Directly through emission sources e.g burning coal releases CO2 2.) Indirectly by altering biophysical or chemical processes that either emit or remove GHGs from/tothe atmosphere e