UPSCpedia: Geograpedia : Greenhouse gas -impact and solution

• A greenhouse gas is a gas in an atmosphere that absorbs and emits radiation within the thermal infrared range.
  

  • This process is the fundamental cause of the greenhouse effect
• In the Solar System, the atmospheres of Venus, Mars, and Titan also contain gases that cause greenhouse effects.
• In order, the most abundant greenhouse gases in Earth's atmosphere are:
  • water vapor
  • carbon dioxide
  • methane
  • nitrous oxide
  • ozone

  In addition to the main greenhouse gases listed above, other greenhouse gases include sulfur hexafluoride, hydrofluorocarbons and perfluorocarbons
  
  

  

  
• Atmospheric concentrations of greenhouse gases are determined by the balance between sources (emissions of the gas from human activities and natural systems) and sinks (the removal of the gas from the atmosphere by conversion to a different chemical compound). 

  • The proportion of an emission remaining in the atmosphere after a specified time is the "Airborne fraction"
  • At the present time, total annual emissions of GHGs are rising
  • For CO₂ the AF over the last 50 years (1956–2006) has been increasing at 0.25 ± 0.21%/year.
  • Between the period 1970 to 2004, emissions increased at an average rate of 1.6% per year, with CO₂ emissions from the use of fossil fuels growing at a rate of 1.9% per year.
  • Based on then-current energy policies, Rogner et al. (2007) projected that energy-related CO₂ emissions in 2030 would be 40-110% higher than in 2000
• Although contributing to many other physical and chemical reactions, the major atmospheric constituents, nitrogen (N₂), oxygen (O₂), and argon (Ar), are not greenhouse gases. 

  • This is because molecules containing two atoms of the same element such as N₂ and O₂ and monatomic molecules such as Ar have no net change in their dipole moment when they vibrate and hence are almost totally unaffected by infrared light.
• Some greenhouse gases are not often listed. For example, nitrogen trifluoride, carbon monoxide (CO) or hydrogen chloride (HCl) absorb IR, these molecules are short-lived in the atmosphere owing to their reactivity and solubility. Because they do not contribute significantly to the greenhouse effect, they are usually omitted when discussing greenhouse gases.
• The global warming potential (GWP) depends on both the efficiency of the molecule as a greenhouse gas and its atmospheric lifetime.

  • effects of methane is about 72 times stronger greenhouse gas than carbon dioxide over a 20 year time frame but it is present in much smaller concentrations so that its total direct radiative effect is smaller.
• The use of CFC-12 (except some essential uses) has been phased out due to its ozone depleting properties. The phasing-out of less active HCFC-compounds will be completed in 2030
• One way of attributing greenhouse gas (GHG) emissions is to measure the embedded emissions (also referred to as "embodied emissions") of goods that are being consumed. 

  • Emissions are usually measured according to production, rather than consumption

  • Per capita emissions in the industrialized countries are typically as much as ten times the average in developing countries.

  • Emissions in Russia and the Ukraine have decreased fastest since 1990 due to economic restructuring in these countries
  • Energy statistics for fast growing economies are less accurate than those for the industrialized countries.

  
• Greenhouse gases can be removed from the atmosphere by various processes, as a consequence of:
  • a physical change (condensation and precipitation remove water vapor from the atmosphere).
  • a chemical reaction within the atmosphere. For example, methane is oxidized by reaction with naturally occurring hydroxyl radical, OH· and degraded to CO₂ and water vapor (CO₂ from the oxidation of methane is not included in the methane Global warming potential).
  • a physical exchange between the atmosphere and the other compartments of the planet. An example is the mixing of atmospheric gases into the oceans.
  • a chemical change at the interface between the atmosphere and the other compartments of the planet. This is the case for CO₂, which is reduced by photosynthesis of plants, and which, after dissolving in the oceans, reacts to form carbonic acid and bicarbonate and carbonate ions.
  • a photochemical change. Halocarbons are dissociated by UV light releasing Cl· and F· as free radicals in the stratosphere with harmful effects on ozone (halocarbons are generally too stable to disappear by chemical reaction in the atmosphere).
• There are a number of technologies that remove emissions of greenhouse gases from the atmosphere:

  • bio-energy with carbon capture and storage and carbon dioxide air capture or to the soil as in the case with biochar. 
  • It has been pointed out by the IPCC, that many long-term climate scenario models require large scale manmade negative emissions in order to avoid serious climate change.
• During the late 20th century, a scientific consensus evolved that increasing concentrations of greenhouse gases in the atmosphere are causing a substantial rise in global temperatures and changes to other parts of the climate system, with consequences for the environment and for human health.

• Emmision Trading - Cap and Trade method: