Context: Rising sea levels in the Indian Ocean are primarily caused by human-induced warming (GHGs) linked to climate change, a recent study by the Indian Institute of Tropical Meteorology (IITM) in Pune has found. It poses an imminent threat to coastal communities, low-lying islands, and marine ecosystems.

Greenhouse Gases (GHGs)

• About: A greenhouse gas is a gas that absorbs and emits infrared radiation. 

o They absorb infrared energy (heat energy) emitted from the earth’s surface and reradiates it back to the earth’s surface. 

o They contribute to the Greenhouse Effect, which is the resultant heating effect.

• Most abundant greenhouse gases in Earth’s atmosphere: Water vapour, Carbon dioxide, Methane, Nitrous oxide, Ozone, Chlorofluorocarbons, Hydrofluorocarbons.

o Among the greenhouse gases, only water vapour can absorb both incoming (UV) and outgoing (infrared) radiation.

o Oxides of Nitrogen with general formula NOx - NO, NO2 - Nitrogen oxide, Nitrogen dioxide etc. are global cooling gases.

• Other GHGs: Carbon monoxide, fluorinated gases, chlorofluorocarbons (CFCs), black carbon (soot), and brown carbon.

o Carbon monoxide (CO) is not considered a direct greenhouse gas, mostly because it does not absorb terrestrial thermal IR energy strongly enough. 

o But CO is able to modulate the production of methane and tropospheric ozone.

• Global Initiative to fight GHGs: Kyoto protocol, Paris Agreement, SDG (2030) etc.