A greenhouse gas is a gas that absorbs and emits infrared radiation. They absorb infrared energy (heat energy) emitted from the earth’s surface and reradiates it back to the earth’s surface. This is an important topic in the environment and ecology section of the UPSC Syllabus.
What are Greenhouse Gases?
- In simple terms, gases that trap heat in the earth’s atmosphere are known as Greenhouse Gases, abbreviated as GHGs.
- They contribute to the Greenhouse Effect, which is the resultant heating effect.
Greenhouse Effect Explanation
- A greenhouse or a glasshouse is a closed glass structure in which plants are grown in regulated climatic conditions.
- In such a structure, the solar radiation passes through the glass and is absorbed by the floor, earth, and other contents inside.
- They in turn, become warmer, and reradiates the energy as infrared (heat) radiation which are of longer wavelength.
- This radiation cannot escape from the glass since glass cannot transmit infrared radiation. Thus, the temperature inside the greenhouse increases.
- This is the Greenhouse Effect.
Natural Greenhouse Effect
- Greenhouse Effect is a natural phenomenon.
- It has been happening on earth for millions of years.
- Natural greenhouse effect happens due to water vapour and particles of water present in the atmosphere.
- This phenomenon has enabled life to emerge on land from the oceans.
- This is also the reason the earth has sustained life as it maintains an average temperature of 15oC on earth.
- But for this effect, the average temperature would have been around -17oC and life would not have existed.
Greenhouse Gases Examples
The Primary GHGs are:
- Water vapour
- Carbon dioxide
- Nitrous oxide
Other GHGs are carbon monoxide, fluorinated gases, chlorofluorocarbons (CFCs), black carbon (soot) and brown carbon.
Among the greenhouse gases, only water vapor can absorb both incoming (UV) and outgoing (infrared) radiation.
- Since the dawn of the Industrial Revolution, the carbon dioxide content in the atmosphere has been steadily increasing.
- From 280 ppm in 1750, it has risen to 406 ppm in 2017.
- Most of the anthropogenic carbon dioxide emissions arise due to the burning of fossil fuels, and also from deforestation, soil erosion and agriculture.
- If GHG emissions continue unchecked, by the end of this century, the global temperatures may increase by 5oC, causing global warming.
- There will also be other climatic repercussions like melting of polar ice caps, melting of the Himalayan snow caps, increased occurrence of El Nino, etc.
- Over many years, there will also be a rise in sea level leading to a submerging of many coastal places, islands, etc.
- It will also lead to a loss of ecosystems like marshes and swamps.
For more on UPSC Geography topics, you can refer to our NCERT Notes for Geography.