Methane is known as ..............
Marsh gas
Methane (CH₄) is the simplest hydrocarbon and the main component of natural gas.
It is produced in marshes and wetlands by the anaerobic decomposition of plant matter, which is why it is commonly called marsh gas.
Laughing gas is nitrous oxide (N₂O) and tear gas is a lachrymatory agent like CS; methane is itself a potent greenhouse gas, so 'non-greenhouse gas' is incorrect.
Hence, Marsh gas.